1000BASE-ZX SMF with a distance limitation of 70km.
1000BASE‑T (aka: IEEE 802.3ab) Twisted-pair cabling (Cat5, Cat5e, Cat6, Cat7) up to 100 meters. Wikipedia
100GBASE-ER4 supports 100Gbps on SMF media up to a distance of 40km.
10BASE2 (aka: cheapernet, thin Ethernet, thinnet, and thinwire) Variant of Ethernet that uses thin coaxial cable terminated with BNC connectors and T connectors. Deprecated by IEEE 802.3 as of 2011. Wikipedia
10BASE5 (aka: thick Ethernet or thicknet) first commercially available variant of Ethernet. Used RG-8 coaxial cable and vampire tap network connectors. IEEE 802.3 has deprecated this standard for new installations as of 2003. Wikipedia
10GBASE-ER (extended reach) Has a reach of 40 kilometres (25 mi) over engineered links and 30 km over standard links. Wikipedia
10GBASE-LR (long range) SMF media type. Maximum distance limitation of 10km. Wikipedia
10GBASE-SR (aka: 10GBASE Short Range) Port type for multi-mode fiber and uses 850 nm lasers. Supports 10Gbps up to 300 meters. 10GBASE-SW used for WANs. Wikipedia
2001: IPv6 global unicast address.
2001::/32 Teredo tunneling address. Wikipedia IANA
2002::/16 6to4 address. Wikipedia
5G 5th generation cellular network. Expected to become a standard in the early 2020s Wikipedia
8080 An alternate to HTML's port 80.
::/128 (::) Unspecified IPv6 address.
::1/128 (::1) IPv6 loopback address.
A DNS host address record. Wikipedia RFC 1035
A5 Used to encrypt GSM cell phone communications.
AAAA DNS IPv6 host address record. Wikipedia Wikipedia RFC 3596
access attack An attack that allows unauthorized access to computer resources. Wikipedia
Access Control Entry (ACE) (aka: ACL statement) A single line in a ACL. Can have sequence numbers to identify each entry. Wikipedia
Access Control List (ACL) Set of rules to block or allow packets. ACLs can also be used for specifying internal hosts for NAT and identifying traffic for QoS. Can have one ACL per interface, per direction, per protocol. Two types, standard ACL and extended ACL. IPv4 ACLs can be named or numbered while IPv6 ACLs can only be named. IPv6 ACLs are equivalent to IPv4 extended ACLs. Wikipedia
access control system Verifies a person's identity and that they are an authorized user. Wikipedia
Access Layer Where users connect to or "access" the network. Wikipedia Netacad Netacad Cisco
Access Point (AP) A connection, typically wireless, into a network. Wikipedia
Access Point Name (APN) Wikipedia
Access server Device used for remote entry into a network to configure devices. Wikipedia YouTube
acknowledgment number (ACK) 1-bit flag in a TCP header. Acknowledges a valid field. Wikipedia Wikipedia
ACL Statement (aka: Access Control Entry) A single line in an ACL.
active hub (deprecated) Type of hub that amplifies and cleans up the signal before broadcasting to all other ports. Deprecated by IEEE 802.3 as of 2011. Wikipedia
active state Where the router actively searches for a new path to the destination in an EIGRP route. An EIGRP route would go into the active state if the successor is down or if there was no feasible successor. Wikipedia
Active Virtual Forwarder (AVF) Each gateway with an assigned virtual MAC address. GLBP group can have up to 4 AVFs. Extra AVFs (more than 4) become SVF. Wikipedia
Active Virtual Gateway (AVG) The first router elected as a gateway in a GLBP group. Highest priority is elected. Assigns a virtual MAC address to each member of the GLBP group. Next highest priority of remaining gateways is elected the SVG. Wikipedia
active-standby Mode of NIC redundancy that uses only one available NIC at a time.
ad hoc Wireless LAN topology. When two or more devices are directly connected through a wireless network without extra infrastructure. Wikipedia Wikipedia
Adaptive Security Appliance (ASA) Wikipedia
address resolution Used to find the MAC address associated with an IPv6 unicast address. Similar to ARP for IPv4.
Address Resolution Protocol (ARP) Resolves IPv4 address to MAC address. Maintains a mapping table. Wikipedia
adjacency database One of the three OSPF databases. Contains the neighbor table. Wikipedia
Administrative Distance (AD) Determines the route to install into the IP routing table. The left side of the brackets represent the AD [1/0]. The trustworthiness of a route source in a routing table. 0 = Connected, 1 = Static, 5 = EIGRP summary, 20 = External BGP (eBGP), 90 = internal EIGRP, 100 = IGRP, 110=OSPF, 115=IS-IS, 120=RIP, 170=External EIGRP, 200=Internal BGP, 255=unknown Wikipedia
Advanced Data Communication Control Procedures (ADCCP) Layer 2 protocol. Wikipedia
Advanced Research Projects Agency Network (ARPANET) Funded by the U.S. Department of Defense. Helped create the first router. Originated in 1986. Wikipedia
African Network Information Centre (AfriNIC) Website
AirPrint Allows Apple devices running macOS or iOS to wirelessly print to a compatible printer or print server. First released November 22, 2010. Wikipedia
alternate ports (backup) Configured in a blocking state to prevent loops. Neither end of the trunk is a root port.
American Registry for Internet Numbers (ARIN) Founded April 18, 1997. Wikipedia Website
anycast (one to-nearest) Wikipedia
App Velocity Cisco borderless service. Optimizes the user experience of applications. Cisco Cisco
Apple Filing Protocol (AFP) (formerly: AppleTalk Filing Protocol) Proprietary network protocol and part of the Apple File Service (AFS) that offers file services for macOS and the classic Mac OS. One of several file sharing services including SMB, NFS, FTP, and WebDAV. Wikipedia
AppleTalk Proprietary suite of networking protocols developed by Apple for their Macintosh computers. Wikipedia
Application Layer (OSI Layer 7) Abstraction layer in the internet protocol suite (TCP/IP) and the OSI model. Allows access to network services such as file transfer, electronic mail, and database access. Wikipedia
Application Layer Services Programs that interface with the network and prepare the data for transfer. Wikipedia
Area 0 Main area for an OSPF network Also called the backbone. All areas must be connected to area 0.
Area Border Router (ABR) Has interfaces attached to multiple OSPF areas. Advertises networks learned from the type 1 LSAs to other areas as type 3 LSAs. Wikipedia
ARP cache Collection of ARP entries, which map IP addresses to MAC addresses. Created when a hostname is resolved to an IP address and then an IP address is resolved to a MAC address. Either static or dynamic, but mostly dynamic. Wikipedia Petri
Asia Pacific Network Information Centre (APNIC) Wikipedia Website
asterisk * A route in a routing table that is a candidate for a default route. Wikipedia
Asymmetric Digital Subscriber Line (ADSL) Faster download speed than upload speed. Wikipedia
Asynchronous Not requiring a clock rate. Wikipedia
Asynchronous Transfer Mode (ATM) A packet-switched WAN. Works on public and private networks. Small cells of fixed length are good for voice and video traffic because it maintains good signal. Wikipedia
ATM cells Always have a fixed length of 53 bytes. (5 byte header, 48 byte payload.) Wikipedia
Automatic Private IP Addressing (APIPA) (aka: auto-IP) Microsoft's name for an IPv4 link-local address. Addresses are assigned in the class B 169.254.0.0 to 169.254.255.255 range. Typically the result of a DHCP error. TechNet Wikipedia
automatic summarization Converts addresses into classful. Wikipedia
Autonomous System (AS) Collection of routers under a common administration such as a company or organization. Wikipedia
Autonomous System Boundary Router (ASBR) A router located between an OSPF routing domain and a non-OSPF network. Wikipedia
AUX port Similar to a console port but configuration occurs through a dial-up connection. Wikipedia
backbone cabling Connects the equipment and telecommunication rooms. Wikipedia
backbone router Has at least one interface in OSPF area 0.
Backup Designated Router (BDR)
backup ports (alternate) Configured in a blocking state to prevent loops.
Backward Explicit Congestion Notification (BECN) Frame Relay congestion-notification bit. Wikipedia Wikipedia
bandwidth (aka: Throughput) The amount of data that can be transferred in a given period.
Basic Service Area (BSA) The coverage area where devices in a BSS can communicate.
Basic Service Set (BSS) One access point connecting all wireless devices.
Basic Service Set Identification (BSSID) The formal name of a BSS identified with the AP's MAC address. Wikipedia
Berkeley Internet Name Domain (BIND) Name daemon. The message format used by BIND is the most widely used DNS format on the internet. Runs on a DNS server. Originally developed in the early 1980s by four UC Berkeley students. Wikipedia
best effort (UDP) Packet delivery is not guaranteed. Does not acknowledge if the data is received.
best path Network path with lowest metric.
Better Approach To Mobile Adhoc Networking (B.A.T.M.A.N.) Routing protocol. Wikipedia
bit interleaving Keeps track of the number and sequence of bits so they can be reassembled on arrival. Wikipedia
bits per second (bps) A measurement of the data transfer rate. Wikipedia
Bitstream A sequence of bits. Wikipedia
Bluetooth (IEEE 802.15) Wireless standard that operates using short-wavelength UHF radio waves in the ISM band from 2.4 to 2.485 GHz to form personal area networks (PANs). Packet-based protocol with a master/slave architecture. One master may communicate with up to seven slaves in a piconet. Devices operate at very low power levels of approximately 1 milliwatt (mW). Invented by Dutch electrical engineer Jaap Haartsen, working for telecom vendor Ericsson in 1994. Named after the Denmark King, Harald Bluetooth because he united Denmark and Norway just as the protocol did for technology. Wikipedia (Bluetooth) Wikipedia (Harald Bluetooth) Website
Bluetooth 5 Increased signal range to 40 meters (~130 ft.) and offers playback on multiple devices. Announced June 16, 2016. First available in the Samasun Galaxy S8 April 21, 2017. Later availabe on the iPhone 8 September 22, 2017. Wikipedia YouTube (MKBHD)
Bootstrap Protocol (BOOTP) A precursor to the DHCP protocol. BOOTP is a network protocol used to obtain IP address information during bootup Wikipedia
Border Gateway Protocol (BGP) Exterior gateway routing protocol, path vector, classes. Designed to share prefix information between different autonomous systems. Version 1 was introduced in June 1989 under RFC 1105. Wikipedia RFC 4271 RFC 1105
Borderless Network The Cisco Borderless Network Architecture is a network solution. YouTube
botnet Computers connected to complete certain tasks. Generally looked upon in a negative way as they can be used to send out spam or perform DDoS attacks. Wikipedia
bridge Network device that operates at OSI Layer 2. Joins similar topologies and divides network segments into multiple collision domains. Isolates network traffic and prevents unwanted traffic from entering a network segment where there are no recipients. More intelligent that a repeater but a router is needed to stop broadcast or perform path selection. Wikipedia
bridge ID (BID) (Bridge priority + MAC address.) Switches with the lowest BID become the root bridge. An exchange of Wikipedia
bridge priority Helps in the root bridge election process. Switch with the lowest priority becomes the root bridge. Default on Cisco switches is 32768. 0 is the highest priority.
Bridge Protocol Data Unit (BPDU) Used by spanning tree to communicate between switches. If a BPDU frame is seen on a PortFast configured interface, it will shut down the interface to prevent a loop. Wikipedia
Bring Your Own Device (BYOD) Wikipedia
broadband Wikipedia
broadcast address The address that is used to send data to all hosts on a subnet. For a /24 subnet, the broadcast would be 255.255.255.0.
broadcast domain The area limited broadcasts can be sent. All hosts on a local network. Separated by a router. Can also be separated by VLAN. Wikipedia
broadcast multi-access network Multiple router connected over Ethernet.
broadcast storms When broadcast frames form layer 2 loops and consume all bandwidth. Layer 2 LAN protocols can't eliminate loops on their own. A Layer 3 protocol is needed to fix the problem because they use routing tables.
broadcast transmission Sending a packet to all nodes in the network. Examples include ARP and DHCP. Usually restricted to the local network. Can be a directed broadcast or limited broadcast.
Burned In Address (BIA) Also known as a MAC address. Wikipedia
C Indicates a directly connected network in a routing table. Wikipedia
Cable Modem Termination System (CMTS)
cable television (CATV) (originally stood for: Community Access Television, Community Antenna Television) System of delivering television programming to paying subscribers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fiber-optic cables. Wikipedia
Carrier Sense Multiple Access (CSMA) Protocols based on CSMA are non-deterministic. (Media independent.)
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Wikipedia
Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) Can increase latency in a WLAN. Adds a random delay before transmitting data in an attempt to avoid collisions. Sends a message across the media before it sends a frame. Wikipedia
Catalyst Brand of network switch from Cisco. Website Wikipedia
Category X cable (Cat X) Type of unshielded twisted pair (UTP) cable.
| Cat 1 | Used for telephone wiring. 1 MHz maximum transmission, which is not suitable for data. |
| Cat 2 | 4 MHz maximum transmission. (4Mbits) |
| Cat 3 | Used for telephone wiring. Was also used for computer networks during the 1990s. |
| Cat 4 | 20 MHz maximum transmission. (16Mbps) |
| Cat 5/5e | 100 MHz maximum transmission. Up to 1000BASE-T (Gigabit Ethernet). |
| Cat 6 | 250 MHz maximum transmission. Up to 10GBASE-T (10-Gigabit Ethernet). |
| Cat 7 | |
| Cat 8 |
Central Office (CO) Local service provider building that connects the CPE to the provider network. Wikipedia
Channel Service Unit/Data Service Unit (CSU/DSU) Layer 1 device. Digital leased lines require both a CSU and a DSU, even if in separate devices. CSU terminates digital signal. DSU converts line frames into frames readable by the LAN. Wikipedia
circuit-switched network Uses a dedicated path during transmission. PSTN and ISDN are two examples of a circuit-switched WAN. Wikipedia
Cisco Adaptive Security Appliance (ASA) Firewall from Cisco. Two firewall modes of operation: routed mode and transparent mode. Basic configs:
en clock set 9:30:00 9 FEB 2014 conf t hostname ASA-1 domain-name ccnasecurity.com enable password class interface vlan 1 description Private inside LAN nameif inside security-level 100 ip add 192.168.1.1 255.255.255.0 interface e0/1 description Physical inside interface switchport access vlan 1 no shut interface vlan 2 description Public outside connection nameif outside security-level 0 ip address 209.165.200.226 255.255.255.248 int e0/0 description Physical outside interface switchport access vlan 2 no shutCisco Catalyst 2960-X Series of network switch from Cisco. Announced June 4, 2013. Released July 2013. Website Wikipedia Cisco Blog
Cisco Catalyst 2960X-24PD-L 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Catalyst 2960X-24PS-L 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Catalyst 2960X-24PSQ-L 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Catalyst 2960X-24TD-L 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Catalyst 2960X-24TS-L 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Catalyst 2960X-24TS-LL 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Catalyst 2960X-48FPD-L 24-port network switch from Cisco. Released May 24, 2013. Website
Cisco Certified Entry Networking Technician (CCENT) Website Wikipedia
Cisco Certified Internetwork Expert (CCIE) Wikipedia
Cisco Certified Network Associate (CCNA) Wikipedia
Cisco Certified Network Professional (CCNP) Wikipedia
Cisco Common Classification Policy Language (C3PL) Configures ZBF policies. Cisco
Cisco Connection Online (CCO) Account used on cisco.com. Cisco
Cisco Express Forwarding (CEF) Default forwarding mechanism used on IOS 12.0 or later. Wikipedia
Cisco High-Level Data Link Control (cHDLC) (aka: Cisco HDLC.) Cisco proprietary version of HDLC. Supports multi-protocol environments. Wikipedia
Cisco Unified Computer System (Cisco USC) Line of scalable servers form Cisco. Announced March 2009. First installed September 1, 2009. Wikipedia Cisco Press Release
Class A address block 0.0.0.0/8 - 127.255.255.255/8 Wikipedia Wikipedia
Class B address block 128.0.0.0/16 - 191.255.255.255/16 Wikipedia Wikipedia
Class C address block 192.0.0.0/24 - 223.255.255.255/24 Wikipedia Wikipedia
Class D address block Multicast addresses.
Class E address block Experimental addresss.
classful Only Class A, B, or C address. (10.0.0.0/8, 172.16.0.0/16, 192.168.0.0/24.) Wikipedia
classless Any class of address. (/8, /25, /30...)
Classless Inter-Domain Routing (CIDR) RFC 1519
clock rate The rate data is transmitted. Configured on DCE interfaces. Wikipedia
clock signal Wikipedia
clock skew An issue along parallel communication where information does not arrive at the same time. Wikipedia
coaxial Wikipedia
Code-Division Multiple Access (CDMA) Wikipedia
Collaboration Meeting Room (CMR) Collaboration tool combining video, voice, and content sharing. Cisco YouTube
collapsed core model Core and distribution layers collapsed into a single device. YouTube
collision When two or more demands are made simultaneously on equipment that can handle only one at any given instant. (i.e. collision domain) Wikipedia
collision domain Physical network segment where data packets may collide with one another while being sent. CSMA/CD and CSMA/CA can be used to detect or avoid collisions on Ethernet or wireless LANs respectively. Wikipedia
Common Address Redundancy Protocol (CARP) Open standard for first-hop redundancy. Provides functionality similar to VRRP and to Cisco's HSRP. Wikipedia
CompTIA Network+ Released February 28, 2015. Website
congestion control 3 frame-relay congestion-notification bit. (FECN, BECN, ) Wikipedia
connection oriented Must establish a connection before sending data. Wikipedia
console cable Connects through the console port to a host for configuring the device over CLI.
Content Delivery Network (CDN) Globally distributed network of proxy servers deployed in multiple data centers. Wikipedia
Content-Addressable Memory (CAM) table MAC table Wikipedia
Control And Provisioning of Wireless Access Points (CAPWAP) Wikipedia
Controlled media access (controlled access) Devices take turns accessing the media with a token. Can be inefficient with too many devices.
converged network One that transports multiple types of traffic such as voice, video, and data. Most modern netowrks are converged.
convergence The process of failing over from one route to a backup route.
Core Layer The backbone layer between networks. Everything must be fast in this layer. Wikipedia Netacad Netacad
crimper Tool used to make twisted pair network cables.
Crossover Cable (T568A to T568B) An uncommon networking cable. Directly connect like devices together. Wikipedia
crosstalk Interference between twisted-pair copper wires caused by the magnetic field around the adjacent pair of wire. Wikipedia
Customer Premises Equipment (CPE) Devices and wiring located on the enterprise edge, connected to a carrier link. Wikipedia
Data Communications Equipment (DCE) Female end of a serial connection. (used for clock rate. modem) Devices that put data on the local loop. Wikipedia
Data Encapsulation Wikipedia YouTube
Data Link Control (DLC) Wikipedia
Data Link Layer (OSI Layer 2) Packages bits of data from the physical layer into frames. These frames are then delivered between nodes on the same network level. Wikipedia
Data Stream Interface (DSI) Session layer used to carry Apple Filing Protocol traffic over TCP. Wikipedia
Data Terminal Equipment (DTE) Male side of a serial WAN connection. Wikipedia
Data-Link Connection Identifier (DLCI) Uniquely identify a VC (data-link) connection. PVCs and DLCIs ensure bidirectional communication from DTE to DTE. Only significant on Wikipedia
Data-Over-Cable Service Interface Specification (DOCSIS) Wikipedia
datagram Basic transfer unit in a packet-switched network.
| OSI Layer | datagam |
|---|---|
| Layer 4 | segment |
| Layer 3 | packet |
| Layer 2 | frame |
| Layer 1 | Chip (CDMA) |
de-encapsulation Process of un-encapsulating packet. Essentially encapsulation in reverse. Layer 2 --> Layer 7. Wikipedia
default gateway The IP address of a router that is the exit or "door" to another network. Typically this address is the first or last useable host address for that subnet. Wikipedia
default route Where packets go when it does not match a route in the routing table. 0.0.0.0/0 for IPv4, ::/0 for IPv6. Wikipedia Cisco
default static route a static route with 0.0.0.0/0 as the destination address. All IP packets that do no have a learned static route will be sent here. This is known a Gateway of Last Resort when configured.
default-information originate Propagates a default static route in router updates.
delay (aka: latency) Network quality issue measuring the time required for a packet to travel from the source to the destination. Wikipedia
demarcation point (DMARC) Separates customer from service provider equipment. Wikipedia
Dense Wavelength-Division Multiplexing (DWDM) Uses optical (fiber) to transmit data over a WAN connection. Multiplies the amount of bandwidth for a single strand fiber. Enables bidirectional communications. 10Gbps multiplexed signal. Multiplex more than 80 channels or wavelengths on single fiber. Supports SONET and SDH. Wikipedia
designated port All non-root ports permitted to forward traffic. Selected per trunk.
Designated Router (DR) uses multicast address 224.0.0.5 for updates.
Destination IP Address Contains a 32-bit binary value that represents the destination IP address of the packet.
destination MAC address Part of an Ethernet frame.
Destination network The address of a remote network and how that network was learned in a routing table.
DHCP snooping Wikipedia
Dialed Number Identification Service (DNIS) Wikipedia
dialup A private WAN infrastructure. Limited to speeds less than 56Kbps due to the PSTN.
dialup modem Wikipedia
Differentiated Services (DiffServ) (aka: soft QoS) Prioritized model to QoS. Marks packets according to the type of service they desire. Most modern QoS configurations are based on the DiffServ approach. Wikipedia
Differentiated Services Code Point (DSCP) (formerly: Type of Service (ToS) field) QoS marking that uses the first 6 bits in the DS Byte of an of an IPv4 packet header. Wikipedia (Differentiated Services) Wikipedia (IPv4 Header) Wikipedia (Quality of Service)
Diffusing Update Algorithm (DUAL) Algorithm used by IGRP and EIGRP. Generates loop-free and backup paths. Developed by Dr. J.J. Garcia-Luna-Achieves at SRI International. Wikipedia
Digital Serial Interface (DSI) Protocol for controlling lighting in buildings. Wikipedia
Digital Signal 0 (DS0) Dedicated line (not shared) at 64Kbps. 24 bundled is a DS1 line or T1 line. Wikipedia
Digital Signal 0 (DS0) Adapter Cisco
Digital Signal 1 (DS1) (T1 line) 1.544Mbps bandwidth Wikipedia T1Rex
Digital Signal 3 (DS3) 44.736Mbps Wikipedia
Digital Subscriber Line Access Multiplexer (DSLAM) Wikipedia
Direct-Sequence Spread Spectrum (DSSS) Spread spectrum modulation technique used to reduce overall signal interference. Modulates data over an entire range of frequencies using a series of symbols called chips which are shorter in duration than a bit. Chips are transmitted at a higher than normall rate and include random data making it difficult to eavesdrop. Supported by 802.11b and 802.11g. Wikipedia
directed broadcast Broadcaster sent to all hosts on a specific network such as non-local network. Routers do not forward these by default.
directly connected static route Static route that uses only the exit interface.
Distributed Coordination Function (DCF) Used with CSMA/CA on WLANs to prevent collisions with random back off timers. Wikipedia
Distribution Layer Forwards traffic between local networks using Layer 3 devices with ACLs and QoS. Netacad
DNS query Request for name resolution. Wikipedia
DNS zone transfer Can be either AXFR (full transfer) or IXFR (incremental transfer) Wikipedia
domain name Uniquely identifies parts of the internet such as a website. Easier to remember than an IP address. Wikipedia
Domain Name System (DNS) (aka: Domain Name Service) (UDP port 53) Translates domain names such as google.com into IP addresses. Originaly published in RFC 882 and RFC 883 November 1983. Wikipedia RFC 882 RFC 883 Cisco (Configuring DNS on Cisco Routers)
Don't Fragment (DF) A router will attempt to fragment a packet that is too big, unless the packet has its don't fragment (DF) bit set. If a packet does exceed an interface's MTU and has its DF bit set, the router drops the packet.
DROTHER A router that is not a DR or a BDR in an OSPF Cisco
duplex settings half duplex and full duplex
Dynamic Domain Name Service (DDNS) Automatically updates the name server in a domain name system. Wikipedia
Dynamic Host Configuration Protocol (DHCP) (RFC 2131) Used to assign an IP address, subnet mask, default gateway, and DNS server address to a host. When a host connects to the network it will broadcast a DHCPDISCOVER message. A DHCP server send a DHCPOFFER back to the host which contains the IP address and subnet mask to be assigned as well as the IP address of the DNS server and default gateway. If multiple offers were received, it will chose one with DHCPREQUEST. The server will send back a DHCPACK to acknowledge the lease is set.
| DHCPDISCOVER-->DHCPOFFER-->DHCPREQUEST-->DHCPACK |
Dynamic Host Configuration Protocol version 6 (DHCPv6) A method for automatically assigning IPv6 global unicast addresses. Similar to DHCP for IPv4. Can be used along with SLAAC.
Dynamic NAT (DNAT) (aka: many-to-many) Many inside local user (a network) are mapped to a pool of inside global addresses.
dynamic routing protocol (EIGRP, RIPv2
Dynamic Trunking Protocol (DTP) Cisco proprietary. Wikipedia
E1 Type of dedicated leased line. Contains 32 64Kbps DS0 channels for a total bandwidth of 2.048Mbps. Wikipedia
E3 Type of dedicated leased line. Contains 16 DS1 channels for a total bandwidth of 34.4Mbps. Wikipedia
edge router Router on the parameter of a network. Three areas to secure: physical security, router hardening, operating system security.
EIGRP composite metric
| K1 | (bandwidth) | 1 |
| K2 | (load) | 0 |
| K3 | (delay) | 1 |
| K4 | (reliability) | 0 |
| K5 | (reliability) | 0 |
EIGRP Convergence neighbors>topology>routing table Wikipedia
EIGRP external route Default administrative distance of 170. Shown in a routing table with EX. Wikipedia
EIGRP internal route default administrative distance of 90 Wikipedia
EIGRP IPv4 Messages Have a destination address of 224.0.0.10 and a source address of the outbound interface. Wikipedia
EIGRP IPv6 Messages Have a destination all-EIGRP-routes link-local multicast address of FF02::A and the IPv6 link-local address of the exit interface as the source. Wikipedia
EIGRP Metric The lowest bandwidth of all the outgoing interfaces between source and destination. Both EIGRP for IPv4 and IPv6 use bandwidth and delay for their composite metric. Reliability and load can also be used to calculate the metric but are not recommended. Wikipedia
EIGRP neighbor table Where router adjacencies are stored. Wikipedia
EIGRP packets
| Acknowledgement | Used to acknowledge the receipt of any EIGRP packet. Unreliable and unicast. |
| Hello | Used to discover other EIGRP routers in the network. Unreliable delivery and multicast. |
| Query | Used to request specific information from a neighbor router. Reliable delivery and multicast or unicast. |
| Reply | Used to reply to a query. Reliable and unicast. |
| Update | Convey routing information to known destinations. Reliable and multicast or unicast. |
EIGRP successor route Stored in the routing table and the topology table. Wikipedia
EIGRP summary route default administrative distance of 5 Wikipedia
EIGRP topology table Where all learned routes are stored. Wikipedia
EIGRP Update packet Convey routing information to known destinations. Reliable and Multicast or unicast. Wikipedia
encapsulation When the network layer adds IP header information such as the IP address of the source (sending) and destination (receiving) hosts. After header information is added to the PDU, the PDU is called a packet. Wikipedia
Enhanced Data rates for GSM Evolution (EDGE) Wikipedia
Enhanced High-speed WAN interface card (EHWIC) Cisco
Enhanced High-speed WAN interface card slot (EHWIC slot) Cisco
Enhanced Interior Gateway Routing Protocol (EIGRP) Internal gateway, distance vector, classless protocol. Creates and maintains the topology table, neighbor table, and the best path(s) in the routing table. Has an administrative distance of 90 and uses multicast address 224.0.0.10. Protocol number of 88. Uses DUAL. Establishes neighbor adjacencies with hello packets. Can be configured with authentication at the router. Sends out only partial and bounded updates. (Only sends route changes to the routers it affects.) Was originally Cisco proprietary but Cisco released basic functionality to the IETF and it is now an 'open' standard. Introduced in 1993. Wikipedia Cisco RFC 7868
Enhanced Interior Gateway Routing Protocol for IPv6 (EIGRP for IPv6) EIGRP on IPv6 uses multicast address FF02::A. Uses the all-EIGRP-routers link-local multicast address as the destination address for EIGRP messages. The source and destination addresses are the only difference between EIGRP and EIGRP for IPv6. Made available in Cisco IOS, Release 12.4(6)T.
enterprise network A large business environment with many users, locations, and systems. Must have support for critical applications, converged network traffic, diverse business needs, and provide centralized administrative control. Netacad
equal cost load balancing Two or more paths to a destination with the same metric cost.
Ethernet Frame Adds headers and trailers to a Layer 3 PDU. Each section of a frame is called a field. Has no TTL. Two kinds of Ethernet Frames are IEEE 802.3 and Ethernet II. Wikipedia
Ethernet II Based on the DIX Ethernet standard.
[ Preamble (8 bits) | Destination Address (6 bits) | Source Address (6 bits) | Type (2 bits) | Data (PDU, 46-1500 bits) | Frame Check Sequence (4 bits) ]
Ethernet private line (EPL) Wikipedia
Ethernet virtual private line (EVPL) Wikipedia
EtherType (0x0800) Two-octet field in an Ethernet frame. Wikipedia
Evolved High-Speed Packet Access (HSPA+) Wireless broadband service similar to WiMAX. Maximum data rate is 84Mbps.
EX An external EIGRP route. AD is 170. Wikipedia
Experimental Addresses 240.0.0.0 to 255.255.255.254 are listed as reserved for future use. Could technically be used at a latter date but for now are just for testing. RFC 3330
Explicit Congestion Notification (ECN) Part of an IPv4 header. Wikipedia Wikipedia (IPv4 Header)
extended ping Where a source interface or address is specified.
Extended Service Set (ESS) The combination of 2 or more APs (BSSs) through a common wired DS. Identified with an SSID. Wikipedia
Exterior Gateway Protocol (EGP) Used for routing outside an Autonomous System. BGP is the only current EGP and is used by the internet. BGP is often used in place of the name EGP. Wikipedia
FE80::/10 IPv6 link local address. Wikipedia Cisco
Feasible Condition (FC) When a neighbors RD is less than this router's FD to the same destination network.
Feasible Distance (FD) The lowest calculated metric to reach the destination network.
Feasible Successor (FS) next after successor (backup path)
FF01::1 All nodes multicast address IANA
FF02::2 All routers multicast address IANA
FF02::A EIGRP ipv6 multicast IANA
Fiber Channel (FC) Wikipedia
Fiber To The x (FTTx) Generic term for optical fiber in the last mile of broadband connections. Usually just called Fiber To The Home (FTTH). Wikipedia
fiber-optic Type of cable consisting of a thin flexible transparent glass or plastic fiber slightly thicker than a human hair. Can transmit from 100Mbps to 10Gbps for several miles. Uses pulses of light to transmit data making it immune to wiretapping and electrical interference. Two cable types: Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF). First developed in the 1970s. Wikipedia
File Transfer Protocol (FTP) Protocol used for transferring files between systems. Wikipedia
FIN (1 bit) Packet sent to both parties to end a TCP three both parties to end a TCP three-way handshake. Wikipedia
floating static route Backup route to a static or dynamic route. To test a floating static route, shutdown the main link and the route should appear in the routing table.
flood guard Limits the number of devices that can connect to a switch port. Once the maximum number of MAC address is exceeded, the port shuts down. Professor Messer
flow control Manages the flow of data from the sender to ensure the receiver is not overwhelmed. Wikipedia TechTarget
Flow Label Part of an IPv6 header. Wikipedia
Forward Explicit Congestion Notification (FECN) Frame Relay congestion-notification bit Wikipedia
forwarding database One of the three OSPF databases. Contains the routing table.
Forwarding Information Base (FIB) (aka: CAM table) Wikipedia
Fragment Offset Field in an IPv4 packet. Wikipedia
fragmentation When an intermediate device, usually a router, must split up a packet if it is transferring it to a medium with a smaller MTU.
Frame Data at Layer 2. Generic frame field:
[ Frame start | Addressing | Type | Control | Data | Error Detection ]
Frame Check Sequence (FCS) Verifies that a frame was received correctly without error.
Frame encoding technique Converts streams of data bits into a predefined code. Distinguish data bits from control bits. Identify where the frame starts and ends.
Frame Relay Access Device (FRAD) Router connected to a Frame Relay network.
Frame Subtype
| 0x00 | Association request frame |
| 0x01 | Association response frame |
| 0x02 | Reassociation request frame |
| 0x03 | Reassociation response frame |
| 0x04 | Probe request frame |
| 0x05 | Probe response frame |
| 0x08 | Beacon frame |
| 0x0A | Disassociation frame |
| 0x0B | Authentication frame |
| 0x0C | Deauthentication frame |
Frame Type
| 0x0 | Management Frame |
| 0x1 | Control Frame |
| 0x2 | Data Frame |
Frequency-Division Multiple Access (FDMA)
Frequency-hopping spread spectrum (FHSS)
full duplex Two-way commutation. (cell phone)
fully specified static route Both output interface and the next hop IP address are specified.
gateway The gateway for a network is the router interface to which the network is directly connected. Wikipedia
Gateway Load Balancing Protocol (GLBP) Cisco proprietary protocol similar to HSRP and VRRP but supports load balancing across a max of 4 routers. Up to 1024 virtual routers. Can use clear text or MD5 authentication between group members. Wikipedia
Gateway of Last Resort Also known as the default route. Wikipedia Cisco
Gateway to Gateway Protocol (GGP)
Generic Routing Encapsulation (GRE) Tunneling protocol developed by Cisco. Creates a virtual point-to-point link and encapsulates Layer 3 packets. Has no encryption or authentication of data. By itself GRE is stateless and does not have flow-control. At least 24 bytes of additional overhead for tunneled packets. The original form of VPN. Introduced in 1994 as RFC 1701. Proposed as an IETF standard in 2000 as RFC 2784. Wikipedia RFC 1701 RFC 2784 Cisco
Gigabit Ethernet (GbE) (IEEE 802.3-2008) Wikipedia
Global Positioning System (GPS) Global navigation satellite system managed by the United States with 24 total satellites. 3 satellites are needed to determine location while 4 are required to determine location and elevation. Launched February 1978. Wikipedia
Globally Unique Identifier (GUID) Wikipedia
Gnutella Protocol used for P2P file transfer
goodput (Throughput - traffic overhead = goodput)
GPRS Tunneling Protocol (GTP) Group of IP-based communications protocols used to carry general packet radio service (GPRS) within GSM, UMTS and LTE networks. Wikipedia
H.323 ITU-T standard for A/V transmission through packets. Wikipedia
half duplex Only one device can talk at a time, similar to Nextel push-to-talk. Hubs should only be half duplex.
Halftone Wikipedia
Headend Where signals are first received in a cable network. Data is then distributed downstream to the cable network. Similar to a CO in a telephone network.
hello packet One of the OSPF protocol messages.
hextet Unofficial term for every 16 bit segment in an IPv6 address Wikipedia
Hierarchical Network Design Access layer, Distribution layer, and Core layer. Wikipedia
High-Level Data Link Control (HDLC) (frame header) Supports only single protocol environments. Wikipedia
High-Speed Serial Interface (HSSI) developed by Cisco Wikipedia
High-speed WAN Interface Card (HWIC) Cisco
hold time The amount of time a neighbor should wait before considering the advertising router to be down. Used in EIGRP.
holddown timer Wikipedia
HomeGroup Allows Windwos users to share files across computers on a home network. Introduced with Windows 7 Website Wikipedia Netacad
hop The jump from one outgoing interface on a router to another outgoing interface.
Hop Limit The amount of hops a packet can take before it is dropped.
Horizontal cabling Inside Wiring (IW) or plenum that connects the telecommunication room to individual outlets in the wall or floor. Wikipedia
horizontal cross-connect Where horizontal cabling connects to a patch panel or punch block. Wikipedia
host An end device with a configured IP address.
Hosts file A text file used by an OS to map IP addresses. Windows filepath: "%WinDir%\System32\Drivers\Etc\Hosts" Wikipedia Microsoft Support
Hot Standby Router Protocol (HSRP) Cisco proprietary protocol. Wikipedia RFC 2281 Cisco
HTTP version 2 (HTTP/2) Published as RFC 7540 May 14, 2015. Wikipedia RFC 7540 IETF
hub Basic network connectivity device that repeats any signal it receives on one port to all other ports. Operates at OSI layer 1. Succeeded by switches. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE 802.3. Wikipedia
hub-and-spoke topology Has a WAN link from each remote site when interconnecting multiple sites (for example, multiple corporate locations). Similar to the star topology.
Hybrid Fiber-Coaxial (HFC) Part of the link to the service provider uses fiber while the other part (usually the last mile) uses coaxial cable. Wikipedia
Hypertext Transfer Protocol (HTTP) (port 80) Transfers webpages that make up the World Wide Web (WWW). When a request for a webpage is made to a web server, HTTP specifies the message types used for communication. The three common message types are GET, POST, and PUT. Introduced under RFC 2068 in January 1997. Wikipedia RFC 2068 RFC 2616 RFC 7540
iBook (FireWire) Released September 13, 2000. Wikipedia
IEEE 802.11 Standard for wireless. Wikipedia
IEEE 802.11a-1999 (aka: 802.11a) Wireless standard that operates at 5GHz. Maximum transfer speed of 54Mbps. Ratified in 1999. Wikipedia
IEEE 802.11ac Wireless standard that operates at 5GHz. Transfer speed of at least 1Gbps. Developed from 2008 to 2013. ANSI approved December 11, 2013. he first 802.11ac products from 2013 are referred to as Wave 1, and the newer higher bandwidth products introduced in 2016 are referred to as Wave 2. Wikipedia
IEEE 802.11b-1999 (aka: 802.11b) Wireless standard that operates at 2.4GHz. Maximum transfer speed of 11Mbps. Max range of 802.11b and 802.11g is 32m indoors / 140m outdoors. 802.11b products appeared on the market in mid-1999. The Apple iBook was the first mainstream computer sold with optional 802.11b networking. Wikipedia
IEEE 802.11g-2003 Amendment to IEEE 802.11 with transfer speeds up to 54Mbps on the same 2.4GHz band as 802.11b. Max range of 802.11b and 802.11g is 32m indoors / 140m outdoors. Rapidly adopted by consumers starting in January 2003, well before ratification. Wikipedia
IEEE 802.11i-2004 (802.11i) Amendment to the original IEEE 802.11 witch improved security. Implemented as Wi-Fi Protected Access II (WPA2). Draft standard was ratified on June 24, 2004. Wikipedia
IEEE 802.11n-2009 (aka: 802.11n) Wireless standard that can operate at 2.4GHz or 5GHz and is backward compatible with earlier standards. Maximum transfer rate of 600Mbps. Published October 29, 2009. Wikipedia
IEEE 802.11r-2008 (aka: fast BSS transition (FT)) Published July 15, 2008. Website Wikipedia
IEEE 802.16 (WiMAX) Originally published in 2001. Wikipedia (IEEE_802.16) Wikipedia (WiMAX)
IEEE 802.1Q Standard for VLANs over Ethernet. Similar frame format to 802.3. (4 extra bytes fields.) Uses a FCS to verify frames were received. Supports tagged and untagged frames. Untagged frames are placed on the native VLAN. Wikipedia
IEEE 802.3 Standard for Ethernet Frame.
[ Preamble (7) | Start of frame delimiter (SFD, 1 bits) | MAC Destination Address (6) | MAC Source Address (6 bits) | 802.1Q tag (optional) (4) | Length (2) | 802.2 Header and Data (46 to 1500) | Frame Check Sequence (FCS, 4 bits) ]
Independent BSS (IBSS) (aka: ad hoc) Formed when two wireless network devices are directly connected without an AP. For example; two laptops directly connected wirelessly to transfer files. Wikipedia
infrastructure mode A wireless LAN topology. Wireless devices are connected using another device such as an access point or a wireless router.
ingress filtering Ensures packets come from where they claim. Wikipedia
Integrated Broadband Services (IBBS) Wikipedia
Integrated Services (IntServ) (aka: hard QoS) Parameterized approach to QoS that can make strict bandwidth reservations. Applications use Resource Reservation Protocol (RSVP) to request and reserve resources through a network. Wikipedia
Integrated Services Digital Network (ISDN) Private, circuit-switched, WAN infrastructure. Uses telephone circuits to send data. Wikipedia
Integrated Services Routers (ISRs) Wikipedia
Interface ID Part of an IPv6 global unicast address. The 'host' portion of the address. A single host may have multiple interfaces each with one or more IPv6 addresses.
Interior Gateway Protocol (IGP) Used for routing within an Autonomous System. (RIPv1, RIPv2, IGRP, EIGRP, OSPF, IS-IS)
Interior Gateway Routing Protocol (IGRP) A link-state routing protocol.
International Telecommunication Union (ITU) Defines open standards and protocols used by the data link layer. Wikipedia
internet A network of networks. Wikipedia YouTube (Warriors of the Net)
Internet Architecture Board (IAB) Website Wikipedia
Internet Assigned Numbers Authority (IANA) Assigns port numbers. Wikipedia Website
Internet Control Message Protocol (ICMP) Used by diagnostic tools such as ping and traceroute. Defined in RFC 792 September, 1981. Wikipedia RFC 792
Internet Control Message Protocol version 6 (ICMPv6) ICMP for IPv6
Internet Corporation for Assigned Names and Numbers (ICANN) Wikipedia Website
Internet Engineering Steering Group (IESG) Website Wikipedia
Internet Engineering Task Force (IETF)
Internet Group Management Protocol (IGMP)
Internet Key Exchange (IKE) Phase 1 Authentication. 3 keys exchanged. Main mode or aggressive mode.
Internet Key Exchange (IKE) Phase 2 Key Exchange. IPsec transform sets. unidirectional IPsec SAs.
Internet Message Access Protocol (IMAP) (IMAP: port 143, IMAPS: port 993) Protocol for email retrieval. IMAP Secure (IMAPS) operates over SSL or TLS. Designed by Mark Crispin in 1986. Wikipedia
Internet Printing Protocol (IPP) Proposed by Novell in 1996. Wikipedia
Internet Protocol (IP) The network layer service implemented by the TCP/IP protocol suite. (Connectionless, Best Effort (unreliable), Media Independent.) Wikipedia YouTube
Internet Protocol Flow Information Export (IPFIX)
Internet Protocol Security (IPsec) Authentication Guaranties message comes from the right person and was not forged. (PSK, RSA)
Internet Protocol version 4 (IPv4) (FC 791) In use since 1983 when it was deployed on the Advanced Research Projects Agency Network (ARPANET). An example address would be: 192.168.10.5
Internet Protocol version 6 (IPv6) An IPv6 address is 128 bits long over IPv4's 32 bits. Every 4 bits is represented by a single hexadecimal digit; for a total of 32 hexadecimal values. Not case sensitive. Network portion identified by a prefix (/64). Can range from /0 to /128. Has three address types: Unicast, Multicast, and Anycast. Three address scopes: global, unique-local, and link-local. Draft standard in RFC 2460 December 1998. Standardized in RFC 8200 July 14, 2017. Wikipedia RFC 2460 RFC 8200 Internet Society
Internet Relay Chat (IRC) Wikipedia
Internet Service Provider (ISP) Provide access to the internet. Four things to consider when choosing an ISP:
| Cost |
| Speed |
| Reliability |
| Availability |
Internet Systems Consortium (ISC) Wikipedia
Internet-Draft (I-D) Working documents published by the IETF. Wikipedia IETF
Internetwork Operating System (IOS) Operating System that runs on Cisco networking gear. Can be stored on non-volatile flash a TFTP server. Copied to RAM when device is powered on. Wikipedia YouTube
Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) Wikipedia
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) An IPv6 transition mechanism meant to transmit IPv6 packets between dual-stack nodes on top of an IPv4 network. Wikipedia
intranet internal network of LANs and WANs Wikipedia
Intrusion Detection System (IDS) Monitors network traffic. Developed by SRI International in 1984. Wikipedia
Intrusion Prevention System (IPS) Responds immediately and inspects traffic before it enters the network. Developed during the late 1990s. Wikipedia YouTube
Inverse Address Resolution Protocol (InARP)
IOS update
copy tftp flash:ip addresssource filenameIP Private Branch Exchanges (PBXs)
IP Suite A suite of protocols required for sending and receiving data using the Internet. Wikipedia
IP-Header Identifies the packet characteristics. Significant fields in the IPv4 header include: Version, Differentiated Services (DS), Time-to-Live (TTL), Source IP Address, Destination IP Address.
IPv4 Addresses IPv4 includes, private, network, broadcast, loopback, link-local, TEST-NET, and experimental addresses.
IPv4 embedded Type of unicast address used to help transition from IPv4 to IPv6.
IPv4 packet Contains two parts; the IP Header and the Payload. Does not have subnet mask.
ipv6 address autoconfig Router(config-if)# ipv6 address autoconfig Cisco
IPv6 anycast Unicast address that can be assigned to multiple devices. Packets are routed to the nearest device with that address.
IPv6 default static route prefix is ::/0
IPv6 global unicast A type of IPv6 unicast address. Globally unique and routable (like public IPv4). Current ranges are 2000::/3. Can be configured manually or automatically with SLAAC and DHCPv6. Has a global routing prefix subnet ID and interface ID.
[ global routing prefix, 48 bits | subnet ID, 16 bits | Interface ID, 64 bits ]
IPv6 multicast For sending an IPv6 packet to multiple destinations.
IPv6 unicast Uniquely identifies an interface. These can be Global Unicast, Link-Local, Loopback, Unspecified Address, Unique Local, Embedded IPv4.
IS-IS IGP, link-state, classless protocol. Wikipedia
ISDN BRI Two 64Kbps B channels and one 16Kbps D channel. Used for home and small enterprise. Inadequate for video but works fine for voice.
ISDN PRI 23 64Kbps B T1 (30 B E1) channels and 1 64Kbps D channel (1.544Mbps total).
jitter Network quality issue where there is an uneven arrival of packets.
K9 Branding for Cisco IOS with security features. Cisco Learning Network
key size (key length) measure in bits. Large keys can degrade performance but are more secure. Wikipedia
key space Possibilities that can be generated by a specific key length. Wikipedia
L Local route in a routing table.
Label Switch Router (LSR) MPLS element that makes frame-forwardig decisions based on lables applied to frames.
Large Link-State Database (LSDB)
last mile Wikipedia
Latin America and Caribbean Network Information Centre (LACNIC) Regional Latin-American and Caribbean IP address registry. Wikipedia LACNIC
Layer 1 (physical layer) Transmits Bits across local media. Wikipedia
Layer 2 (data Link layer.) Packages Layer 3 PDUs into frames. Manages access to frames and network media. Wikipedia
Layer 2 address (physical or MAC address) 48 bits long, 6 octets, 12 hexadecimal digits. The first 6 hex numbers indicate the manufacture of the NIC (OUI), the last 6 are serial number of the NIC.
Layer 3 network layer of the OSI model. Wikipedia
Layer 4 Transport layer (TCP, UDP) Wikipedia
Layer 4 Switching Used to filter TCP and UDP packets before they reach Layer 3. HP proprietary.
Layer 5 session layer Wikipedia
Layer 6 presentation layer Wikipedia
Layer 7 (application layer) Wikipedia
Layer 8 user error Wikipedia
leased line Private WAN infrastructure. Dedicated point-to-point connection leased from a service provider. Bandwidth is not shared with multiple customers. Examples include: T1, E1, T3, and E3. Can use multiplexing to transmit multiple conversations over different 64Kbps channels. Terminates on a CSU/DSU device. Wikipedia
level 1 parent route a subnetted level 1 network route. Not an ultimate route.
level 1 route routing table entry with a subnet mask less than or equal to the classful mask of the network address. (Network route, Supernet route, Default route)
level 2 child route a route that is a subnet of a classful network address.
Lightweight Access Point Protocol (LWAPP)
limited broadcast Broadcasts only to hosts on the local network (broadcast domain). Always use destination address o 255.255.255.255. Will not be forwarded by a router.
Link Access Procedure (LAP) Wikipedia
Link Access Procedure for Frame Relay (LAPF) Defines the header and trailer of Wikipedia
Link Access Procedure, Balanced (LAPB)
Link Aggregation Control Protocol (LACP) IEEE 802.3ad protocol used for EtherChannel Modes: On - forces interface to channel. LACP active - interface in active negotiation state. LACP passive - interface in passive negotiating state.
Link State Acknowledgements (LSAck) One of the OSPF protocol messages. Sent after a neighbor adjacency is established.
Link State Advertisement (LSA) Sent after a neighbor adjacency is established. LSAs are flooded to adjacent neighbors until all routers in the area have LSAs.
| type 1 | Router LSA. Also known as router link entries. All routers generate type 1 LSAs. Flooded only inside the area they came from, never go beyond ABR. Link ID is the router ID of originating router. |
| type 2 | Network LSA. Only exists for multi-access and nonbroadcast multi-access. Gives routers information about multi-access networks in the same area. Identify the routers and network addresses of multi-access links. Only generated by a DR. |
| type 3 | Summary LSAs. Advertises networks from other areas. ABR send type 3 LSAs to other areas. Routes are not summarized by default. Link state ID identified by network address. |
| type 4 | Advertise external networks into an OSPF routing domain. Only generated by ABRs. Identifies the ASBR and provides a route to it. |
| type 5 | AS external LSAs. Most summarized by default. |
| type 6 | Multicast OSPF LAS |
| type 7 | Defined for NSSAs |
| type 8 | External attributes LSA for BGP |
| type 9 | Opaque LSAs |
| type 10 | Opaque LSAs |
| type 11 | Opaque LSAs |
Link State Update (LSU) One of the OSPF protocol messages.
link-local address IPv4 addresses 169.254.0.0 to 169.254.255.255 (169.254.0.0/16) can be automatically assigned to the local host by the operating system in environments where no IP configuration is available. These addresses are not routable. The IPv6 address block FE80::/10 is reserverd for link-local unicast addressing. Wikipedia RFC 4291 (Link-Local IPv6 Unicast Addresses)
Link-Local Multicast Name Resolution (LLMNR) Based on DNS. Allows both IPv4 and IPv6 hosts to resolve addresses. Wikipedia
Link-State Database (LSDB) One of the three OSPF databases. Contains the topology table.
Link-State Request (LSR) One of the OSPF protocol messages.
link-state routing protocol Has a complete map of the network. Computes the network topology from its perspective. Requires more hardware resources. OSPF is an example of a link-state protocol.
load balancer (aka: content switch) distributes incoming requests accross multiple servers. All servers contain the same data. Wikipedia
Local Area Network (LAN) A network that is in a small geographical area such as home or office. Wikipedia
Local Connector (LC) (aka: little connectors) Mini Form Factor (MFF) fiber-optic connector popular for use with Fiber-Channel adapters, fast SANs, and Gigabit Ethernet. Developed by Lucent Technologies. Wikipedia
local host Administrative distance is 0.
Local Loop The physical cable that connects the CPE to the CO of a service provider. (The last mile.)
Local Management Interface (LMI) Wikipedia
logical Address (OSI Network Layer 3) Wikipedia
Logical Link Control (LLC) A Layer 2 protocol. Wikipedia
loopback address Can ping 127.0.0.1 to see if NIC is working. Is also a special address a host can use to direct traffic to themselves. Additional loopback addresses include 127.0.0.0 through 127.255.255.255 for IPv4. IPv6 also has ::1/128 and just ::1 for loopback addresses. Wikipedia PC Magazine
MAC database instability When the same broadcast frames are received on a switch, an endless loop can occur. Ethernet frames do not have TTL so they are constantly forwarded, confusing the MAC address table. Wikipedia
Mail Delivery Agent (MDA) Accepts mail form the MTA and preforms the actual delivery. Wikipedia
Mail Exchange (MX) DNS record. Wikipedia
Mail Transfer Agent (MTA) Used to forward email Wikipedia
Mail User Agent (MUA) An email client. Wikipedia
Management Information Base (MIB) SNMP component that defines the structure of SNMP management objects. The structure of these management objects is defined by a managed device's MIB. Interfaces and their details, such as errors, utilization, discards, packet drops, resets, speed and duplex, system memory, utilization of bandwidth, storage, CPU, and memory, are able to be monitored and reported via SNMP. YouTube (SolarWinds)
management ports Ports used for managing a network device.
| Console |
| Telnet |
| SSH |
| AUX port |
Marking QoS mechanism that alters bits within a frame, cell, or packet to indicate how the network should treat that traffic.
Maximum Transmission Unit (MTU) The maximum size of the PDU each medium can transport.
maximum-paths Paths that should be maintained for load balancing.
Media Access Control (MAC) Sublayer of OSI Layer 2. Wikipedia
Media Access Control address (MAC address) (aka: burned-in address, Ethernet hardware address (EHA), hardware address or physical address (not to be confused with a memory physical address)) Unique identifier assigned to a network interface controller (NIC) for communications at the data link layer of a network segment. Wikipedia
Medianet Cisco borderless service. Helps deploy and manage media applications. Metadata YouTube Cisco
metric Quantitative value used to measure the distance to a given network in a routing table. Lower values indicate preferred routes. Wikipedia
Metro Ethernet (aka: metropolitan-area Ethernet, Ethernet MAN) MAN based on Ethernet. Packet-switched WAN. Wikipedia
modem Translates digital signals to analog. Wikipedia
Multi-Mode Fiber (MMF) (aka: multimode fiber) Most often used in horizontal cabling. Can transmit up to 10Gbps for up to 550 meters (1,804 feet) or just over one-third of a mile. Wikipedia
multicast (one to many) Sending a packet from one host to a selected group of hosts, possibly in different networks. Saves bandwidth by only sending one copy of the traffic. IPv4 addresses 224.0.0.0-239.255.255.255 are used for multicast addresses.
| 224.0.0.0-224.0.0.255 | reserved for link-local |
| 224.0.1.0-238.255.255.255 | reserved for globally scoped addresses |
multicast Domain Name System (mDNS) resolves hostnames in networks without a local name server. Wikipedia
multiple frame transmission Multiple copies of unicast frames are sent to the destination.
Multiple Input, Multiple Output (MIMO) Achieves higher throughput by using multiple antennas to transmit and receive. Found in IEEE 802.11n and above. Wikipedia
Multiple Spanning Tree Protocol (MSTP)
multiplexing Process where hosts can support multiple simultaneous sessions over a single link. Wikipedia
Multiprotocol Label Switching (MPLS) A packet-switched WAN. Can be used to deliver any type of packet over a WAN. Elements include; Customer Premises Equipment (CPE), Customer Edge (CE), Edge Label Switch Router (ELSR), Provider Edge (PE), Label, Switch Router (LSR), and Provider (P) routers. Header is 32 bit long, which contains the label. Wikipedia YouTube
NAT translations (xlates) Netacad
Neighbor Advertisement (NA) ND message
Neighbor Discovery Protocol (NDP) Wikipedia
Neighbor Discovery Protocol (NDP)
Neighbor Solicitation (NS) ND message
neighbor table Table in OSPF adjacency database. Lists neighboring routers. Can be viewed on IOS with show ip ospf neighbor.
Network Access Control (NAC) Approach to endpoint security. Wikipedia
Network Access Server (NAS) Also known as an access server. Wikipedia
network address Wikipdedia
Network Address Translation (NAT) Remaps one IP address space into another. Three kinds of NAT: static, dynamic, and overload (PAT). Translation process:
| Inside local | private IP address being translated |
| Inside global | public IP address referencing an inside device |
| Outside local | private IP address referencing an outside device |
| Outside global | public IP address referencing an outside device |
Network Address Translation 64 (NAT64) Similar to NAT for IPv4 but used for IPv6. Wikipedia
Network Administration Control (NAC) Cisco's version of Network Access Control. Wikipedia
Network Based Application Recognition (NBAR) Cisco
Network Basic Input/Output System (NetBIOS) Works at the OSI session layer (layer 5). Developed as an API. Wikipedia
Network Control Protocol (NCP)
Network Discovery Protocol (NDP) Five main NDP messages.
| Router Solicitation (RS) |
| Router Advertisement (RA) |
| Neighbor Solicitation (NS) |
| Neighbor Advertisement (NA) |
| Redirect |
Network Interface Controller (NIC) (aka: network interface card, network adapter, LAN adapter, physical network interface, NIC card) Connects a computer to a network. Wikipedia
Network Interface Device (NID) Demarcation point between the carrier's local loop and the customer's premises wiring Wikipedia
Network Layer (OSI Layer 3) Responsible for packet forwarding including routing through intermediate routers. Addresses data messages and translates logical addresses into physical ones. Wikipedia
Network Layer Protocols IPv4 and IPv6 are the current protocols. IPX, AppleTalk, and CLNS/DECNeT are some other legacy protocols not often used.
Network Load Balancing (NLB) (aka: dual-WAN routing or multihoming) Distributing the workload across multiple paths to provide fault tolerance and improve performance. Wikipedia
Network Management Protocol (NMP)
Network Operations Center (NOC) (aka: Network Management Center) Location used to monitor and control a network. Wikipedia
network route routing table entry that has a subnet mask equal to that of the classful mask.
Network Time Protocol (NTP) (UDP port 123) Synchronizes time across devices in the network. Helps when comparing syslog. Wikipedia Debian Wiki
Network-Aware Applications Can use protocols to communicate with lower level protocols on the OSI and TCP/IP models. Examples include web browsers and Email clients.
next hop The address of the next router interface.
Next Hop Resolution Protocol (NHRP)
nibble 4 bits (half a byte) Wikipedia
node Wikipedia
node port (N_Port) Wikipedia
Non-existent Domain (NXDOMAIN) DNS Knowledge
nonrepudiation (digital signature) Similar to authentication. Cannot refute or "repudiate" the validity of a message. Wikipedia
NT1 ISDN device that interconnects a 4-wire ISDN circuit with a 2-wire ISDN circuit
null0 (0.0.0.0/0) The bit bucket. Packets that don
O In a routing table, 'O' indicates a route that was learned dynamically by OSPF. Learned by type 1 and 2 LSAs. Cisco
O E1 External routes to an AS. Learned by type 5 LSAs Cisco
O E2 External routes to an AS. Learned by type 5 LSAs Cisco
O I Cisco
O IA OSPF Interarea (originated from another area) summary LSAs. Learned from type 3 or type 4 LSAs. Cisco
Object Identifier (OID) Csico YouTube
Object Linking and Embedding (OLE) Microsoft protocol. Wikipedia
Open Shortest Path First (OSPF) (IGP, link-state, classless protocol) Efficient trigger updates. Fast convergence. Easily scalable. Wikipedia
Open Shortest Path First version 3 (OSPFv3) UIGP, link-state, classless protocol. uses Dijkstra's algorithm to make IPv6 routes. Very much like it's IPv4 counterpart, OSPF.
Open Systems Interconnection model (OSI model)
| layer 1 | physical |
| layer 2 | data link |
| layer 3 | network |
| layer 4 | transport |
| layer 5 | session |
| layer 6 | presentation |
| layer 7 | application |
OpenSSH An open source version of SSH typically used on Linux systems. Wikipedia Website
Optical Carrier 3 (OC3) 155.52 Mbps bandwidth leased line. Wikipedia
Optical Time Domain Reflectometer (OTDR) Tool that enables you to locate a break in fiber-optic cable. Wikipedia
Orthogonal Frequency-Division Multiplexing (OFDM) Method of encoding digital data on multiple carrier frequencies. Uses a relatively slow modulation rate for symbols with high data rates. Simultaneous transmission of data over 52 data streams. Supports Supported by 802.11a, 802.11g, and 802.11n. Wikipedia
OSPF area A group of routers that share the same link-state information in their link-state databases. Wikipedia
OSPF message types Used to discover routers and exchange routing information. Packets: Hello, DBD, LSR, LSU, LSAck. Transmitted over IP Wikipedia
OSPF priority Can be a number 1-255. (255 is the highest and is most likely to become a DR.) The DR or BDR is chosen by the highest priority value. A priority of 0 does not become a DR/BDR.DR/BDR. Wikipedia
OSPF route calculation In an OSPF network, all routers calculate the best path to destination within their own area, then the internetwork, and then to external destination networks. Wikipedia
OSPF states
| Down state: | No Hello packets are received. | ||
| Init state: | Hello packets received. | ||
| Two-way state: | DR and BDR election. | ||
| ExStart state: | Negotiate master / slave and DBD packet sequence number. | ||
| Exchange state: | Exchange of DBD packets | ||
| Loading state: | Additional information is sent. | ||
| Full state: | Routers converged. |
outgoing interface The exit interface used when forwarding packets to a destination network.
P2P copyright infringement Sharing copyright files over P2P. Wikipedia University of Washington
packet Data at OSI Layer 3. Wikipedia
packet capture (PCAP) Wikipedia
Packet Filter (PF) Wikipedia
packet length Wikipedia
packet sniffer Monitors packets through the network.
Packet-Switched Network Files are split into many pieces before transmitting and may traverse multiple paths to reach the destination. Frame Relay and ATM are examples of a packet-switched WAN. Wikipedia
packets per second (pps) Measurement of throughput. Wikipedia
parallel Can send multiple bits of information over multiple wires at the same time to theoretically reach the destination faster. Wikipedia
parity Indicates whether a number is even or odd. Wikipedia
parity bit Wikipedia
parity file Wikipedia
parity flag Wikipedia
partial mesh Network topology that balances redundancy with easy management and cost effectiveness.
passive interface Interface that is not receiving updates but can send them. Configured with 'passive-interface' and disabled with 'no passive-interface'.
password recovery
flash_initload_helperdir flash:rename flash:config.text flash:config.text.oldbootpatch panel Wikipedia
payload Contains the Layer 4 segment information and the actual data.
Peer-to-Peer (P2P) Type of network connection. Peers share information without the need of a central server. All devices are technically servers. Wikipedia
Per VLAN Spanning Tree (PVST) Wikipedia
Permanent Virtual Circuit (PVC) (aka: Private Virtual Circuit). Used to carry both voice and data traffic. Preconfigured by the carrier and only operate in DATA TRANSFER and IDLE modes. Supports data rates up to 4Mbps. More common than SVCs. Wikipedia Netacad
physical address (aka: Layer 2 address or MAC address) Used to identify devices at the physical layer (Layer 2). Allows devices to communicate on the same local network. Wikipedia
Physical Layer (OSI Layer 1) The first and lowest layer. Transmits raw bits from one computer to another and regulates the transmission stream over a medium. This layer may be implemented by a PHY chip. Wikipedia
piconet Ad hoc network that links a wireless user group (WUG) of devices using Bluetooth technology protocols. Consists of two or more devices occupying the same physical channel. Allows one master device to interconnect with up to seven active slave devices. Wikipedia
ping Network utility used to test network connectivity between devices. Can also be used to test DNS. Example: ping www.google.com Written by Mike Muuss in December 1983. Wikipedia
ping sweeps Wikipedia
Plain Old Telephone Service (POTS)
Point-to-Point Frame Wikipedia
Point-to-point network Two routers connected over a common link. Wikipedia
Point-to-Point protocol Data link layer protocol. Establishes logical connection (sessions) between two nodes (interfaces).
Point-to-Point Protocol (PPP) Common non-proprietary Layer 2 protocol found on dedicated leased lines. Sends packets over point-to-point links. Offers features such as: multilink interface, looped link detection, error detection, and authentication. Supports PAP and CHAP authentication. Can be configured on interfaces with asynchronous serial, synchronous serial, HSSI, and ISDN. Defined in RFC 1661 July 1994. Wikipedia RFC 1661
Point-to-Point Protocol over Ethernet (PPPoE) Encapsulating protocol for PPP. Typically used with DSL. Wikipedia
pointer record (PTR) Type of DNS record that maps an IP address to a hostname. Defined in RFC 1035 November 1987. Wikipedia RFC 1035
Polyalphabetic cipher Any cipher based on substitution including The Vigen Wikipedia
port Identifies which application data will go to. 0-1023 are well known ports, 1024-49151 are registered ports, 49152-65535 are private and/or dynamic ports. Several ports include:
| Well Known Ports | |
|---|---|
| port 0 | (Legacy) 768 bit key. |
| port 21 | FTP |
| port 22 | SSH |
| port 23 | Telnet |
| port 25 | SMTP |
| port 53 | DNS |
| port 80 | HTTP |
| port 110 | POP3 |
| port 143 | IMAP |
| port 161 | SNMP |
| port 194 | IRC |
| port 443 | HTTPS |
| port 520 | RIP |
| port 531 | Chat (AOL Instant Messenger) |
| Registered Ports | |
|---|---|
| port 1433 | MS SQL |
| port 1812 | RADIUS authentication protocol. |
| port 1863 | MSN Messenger, TCP |
| port 2000 | Cisco SCCP (VoIP), TCP |
| port 2948 | WAP (MMS) |
| port 5004 | (RTP) Voice and video transport protocol. |
| port 5060 | SIP (VoIP) |
| port 8008 | Alternate HTTP |
port 465 (SMTPS) Wikipedia Stack Overflow
Port Address Translation (PAT) Many-to-one address mapping. An extension of NAT also known as NAT overload. YouTube
Port Aggregation Protocol (PAgP) Cisco proprietary protocol for EtherChannel. Modes: On - forces the interface to channel without PAgP. PAgP desirable - interface in active negotiating state. PAgP auto - interface in passive negotiating state
Port Security Prevents MAC address spoofing and MAC table overflows. Can statically assign or dynamically learn MAC addresses to permit. Cisco
Post Office Protocol (POP) (v2, port 109. v3, port 110.) Application layer protocol used for receiving email. First defined in RFC 918 October 1984. Wikipedia RFC 918
Post Office Protocol version 2 (POP2) Defined in RFC 937 February 1985. Wikipedia RFC 937
Post Office Protocol version 3 (POP3) Defined in RFC 1081 November 1988. Wikipedia RFC 1081
Power over Ethernet (PoE) (802.3af)
PPP frames
{ Flag | Address | Control | Protocol | Data | Frame Check Sequence (FCS) } |
Preamble Start of an Ethernet frame. Wikipedia
prefix Number of network bits in the subnet mask. /24=255.255.255.0
Presentation Layer (OSI Layer 6) Translates application layer data to an intermediate form that provides security, encryption, and compression for the data. Wikipedia
private address Private IPv4 address ranges are:
| 10.0.0.0 - 10.255.255.255 | (10.0.0.0/8) |
| 172.16.0.0 - 172.31.255.255 | (172.16.0.0/12) |
| 192.168.0.0 - 192.168.255.255 | (192.168.0.0/16) |
Private and/or Dynamic Ports 49152-65535
Private Virtual Circuit (PVC) (aka: Permanent Virtual Circuit (PVC) Wikipedia
Private VLAN (PVLAN) Edge (protected ports) Cisco
private WAN infrastructure Dedicated (Leased Lines) and Switched (Circuit or packet switched) WANs.
promiscuous mode Where a network adapter is set to captures packets.
Protocol Protocols provide the rules and formats that govern how data is treated.
Protocol Data Unit (PDU) The form that a piece of data takes at any layer.
protocol field Part of a packet header represented by a number to identify the protcol being used in the PDU. 6 is used to indicate TCP, 17 for UDP, 88 for EIGRP, 89 for OSPF.
Protocol-Dependent Module (PDM) Allows EIGRP to route for various Layer 3 protocol packets. (IPv4 and IPv6) Wikipedia
Provider Edge (PE) MPLS element that is the provider's router connecting the customer. Wikipedia
Public Switched Telephone Network (PSTN) A circuit-switched WAN.
public WAN infrastructure Internet. (Broadband, VPN)
PVC status
| ACTIVE | PVC is up |
| DELETED | PVC is not present and no LMI information is being received |
| INACTIVE | Connection to remote host is unavailable |
| STATIC | LMI is disabled on that interface |
Quality of Service (QoS) Suite of technologies that allows you to strategically optimize network performance for select traffic types. Commonly used QoS mechanisms include:
| Classification |
| Marking |
| Congestion management |
| Congestion avoidance |
| Policing and shaping |
| Link efficiency |
| Integrated Services (IntServ) |
| Differentiated Services (DiffServ) |
R In a routing table, 'R' indicates a network that was learned dynamically using RIP.
Random Early Detection (RED) (aka: random early discard, random early drop) QoS tool that seeks to avoid congestion before it becomes an issue on the network. Wikipedia
Rapid PVST+ The Cisco implementation of RSTP on a per-VLAN basis. Netacad
Rapid Spanning Tree Protocol (RSTP) IEEE 802.1w evolution of the original STP 802.1D standard. Wikipedia
Rapid STP (RSTP) (802.1w) Cisco
Real-Time Messaging Protocol (RTMP) (port 1935) Wikipedia
Real-time Transport Protocol (RTP or RTTP) Wikipedia
Received Signal Strength Indicator (RSSI) Measures the power of a wireless signal.
recursive static route A static route that uses an IP address as the next hop rather than an exit interface. Cisco
redistribute When two networks running different routing protocols need to communicate their route can be redistributed. Static routes (0.0.0.0 quad zero) can be used for connecting to ISPs. Cisco
reference model For networking, it clarifies the processes of networking and makes troubleshooting easier. Examples include TCP/IP and OSI.
Regional Internet Registries (RIRs) RIRs are responsible for allocating IP addresses to ISPs.
Registered Jack (RJ) (ISO 8877) Standard connector used in data and telecommunication networks. Wikipedia
Reliable Transport Protocol (RTP) Used in EIGRP. (TCP) Wikipedia
Remote Desktop Protocol (RDP) (TCP port 3389 UDP port 3389) Proprietary Microsoft protocol. Wikipedia
remote host Located on a remote network and have different network addresses.
remote network Network that originate from another router and have different network addresses.
Remote Network Network/packet mode Microsoft TechNet Netacad
remote network entries
{ Router source | Destination network | [Administrative distance/Metric] | Next-hop | Route timestamp | Outgoing interface }
Remote Office / Branch Office (ROBO)
remote route Entry in a routing table that came from a remote network. Can be configured manually or learned dynamically.
repetition control structure (aka: iteration control structure) Series of statements in a loop.
Resource Reservation Protocol (RSVP) QoS IntServ mechanism that reserves resources for an integrated services internet. Operates at OSI Layer 4 (transport). Defined in RFC 2205 September 1997. Wikipedia RFC 2205
Reverse Address Resolution Protocol (RARP) Ethernet type 0x8035.
Riser Cabling (Also known as Vertical cabling) Wikipedia
RJ-45 plug The standard connector used for LANs on Ethernet cable.
Rollover Cable (Console Cable) T658A to reversed T658A. Wikipedia
root bridge Bridge with the smallest (lowest) bridge ID. Switch in STP that determines which redundant paths to block. The root bridge switch can be set with a priority of 0. If multiple devices have a priority of 0, it will chose the one with the lowest MAC address. Wikipedia
root hints Resolve queres for zones that don't exist on the local DNS server. Only use if forwaders are not configured or fail to respond YouTube (Microsoft MCSA/MCSE Learning Channel)
root port Switch ports closest to the root bridge
Round Robin (RR) Network scheduling algorithm. Wikipedia
route poisoning Wikipedia
route resolvability The process used by the routing table to determine the exit interface used to forward a packet.
route source How a route was learned in a routing table. Usually represented by the first letter of the routing protocol or the kind of connection. (i.e. R for a RIP route, C for a directly connected route, S for a static route...)
route summarization (route aggregation) advertising a contiguous set of addresses as a single address with a less-specific, shorter subnet mask.
route timestamp When a route was last heard in a routing table.
router routes packets across different networks and to other devices on the current network. Wikipedia
Router Advertisement (RA) Message sent by IPv6 routers to advertise their presence. Provides addressing information to hosts using SLAAC.
Router Discovery Protocol (RDP)
router ID Both IPv4 and IPv6 use the same 32-bit router ID in EIGRP. Can be configured with the
router on a stick Allows hosts logically separated by a VLAN to communicate. Wikipedia
Router Solicitation (RS) When configured with SLAAC, a host will send an RS message to the router.
routing Choosing the best path through a network. Wikipedia
Routing Information Base (RIB) Also known as the routing table. Wikipedia
Routing Information Protocol (RIP) (Administrative Distance: 120, UDP port 520) Distance-vector routing protocol that uses hop count as a routing metric. Has a maximum hop count of 15. Implements the split horizon, route poisoning and holddown mechanisms to prevent incorrect routing information from being propagated. Uses multicast address 255.255.255.255. Wikipedia
Routing Information Protocol (RIPng) An extension of RIPv2 that supports IPv6. Wikipedia
Routing Information Protocol Version 2 (RIPv2) Uses UDP through port 520. Broadcast 224.0.0.9 Wikipedia
routing loop Where duplicate frames are sent across the network to the same router and get stuck in a loop. Wikipedia
routing protocol How routers communicate with each other. A set of processes, algorithms, and messages used to exchange routing information and populate the routing table with the best path. Wikipedia
routing table Each router or computer has a unique routing table of where to send packets. Volatile. Table in the OSPF forwarding database. [Route source | Destination network | Outgoing interface] Can be shown using route print on Windows, route -n on Linux, and show ip route on Cisco IOS. Wikipedia Microsoft TechNet
running configuration file Current configuration in Cisco IOS
S Identifies a static route created to reach a specific network in a routing table.
Second Level Address Translation (SLAT) (aka: nested paging) Hardware-assisted virtualization technology. Wikipedia
Secure Device Manager (SDM) Management software for Cisco routers
Secure Shell (SSH) A more secure form of telnet that uses port 22 instead of port 23 as in the case of telnet. Cisco Pluralsight blog
Secure Shell (SSH) Configuration Can be configured on a Cisco device with a;
//example |
hostname carter |
aaa new-model |
username cisco password 0 cisco |
ip domain-name rtp.cisco.com |
crypto key generate rsa |
ip ssh time-out 60 |
ip ssh authentication-retries 2 |
line vty 0 4 |
transport input SSH |
Segmentation Dividing a data stream into small pieces.
sequence control structure Series of statements that follow one another.
serial Sends information in a single stream, one at a time. (bidirectional)
Serial Line Internet Protocol (SLIP) standard protocol for point-to-point serial connections using TCP/IP Netacad
Serial Link Address Resolution Protocol (SLARP)
service sequence-numbers Service on networking devices that puts sequence numbers in syslog messages.
Service Set Wikipedia
Service Set Identifier (SSID) (aka: BSSID) Associated with the MAC address on a wireless Access Point (AP). Identify logical networks (including extended service sets) and serve as the "network name". Wikipedia
Serving Area Interface (SAI) Outdoor enclosure or metal box that allows access to telecommunications wiring. Wikipedia
Session Initiation Protocol (SIP) (port 5060) Wikipedia YouTube
Session Layer (OSI Layer 5) Establishes and controls data communication between applications operating on two computers. Wikipedia
Shielded Twisted Pair (STP) A type of twisted pair cabling with a layer of braided foil shielding surrounding the wires to reduce electrical interference. Wikipedia
signal-to-noise ratio (SNR) Wikipedia
Simple Mail Transfer Protocol (SMTP) (TCP port 25) Transfers mail messages and attachments. Wikipedia
Simple Mail Transfer Protocol Secure (SMTPS) port 465 Wikipedia
Simple Network Management Protocol (SNMP) Service uses port 161, trap uses port 162. Uses SNMP managers, agents, and MIBs. Consumes more bandwidth than Syslog. First defined in RFC 1067 August 1988. Wikipedia RFC 1067 Cisco (Configuring SNMP) Netacad CCIE or Null!
Simple Network Management Protocol version 1 (SNMPv1) Community-based form of security. Able to access an agent's MIB as defined by ACLs and passwords. Offer minimal security features. (No encryption or authentication.) Defined in RFC 1157 May 1990. Wikipedia RFC 1157
Simple Network Management Protocol version 2c (SNMPvc2) Community-based form of security. Able to access an agent's MIB as defined by ACLs and passwords. Offer minimal security features. (No encryption or authentication.) Wikipedia
Simple Network Management Protocol version 3 (SNMPv3) Authenticates and encrypts packets between management devices. Defined in RFC 5590 June 2009. Wikipedia RFC 5590
Simple Service Discovery Protocol (SSDP) October 28, 1999 Wikipedia IETF
single area OSPF Uses area 0. Good for small campus. Has a large routing table because summarization is disabled by default. LSDB. Frequent SPF algorithm calculations.
Single-Mode Fiber (SMF) Commonly used as backbone cabling or cable in phone systems. Light travels straight down the fiber and does not bounce off the fiber walls. Can transmit 10Gbps up to 40 kilometers (25.85 miles). Wikipedia
Small and Medium-sized Businesses (SMB)
Small and Medium-sized Enterprise (SME)
Small Form-factor Pluggable (SFP) Wikipedia
Small Office/Home Office (SOHO)
Smart Jack Type of Network Interface Device (NID) that includes circuitry to perform such functions as converting between framing formats on a digital circuit (T1), remote diagnostics, and regenerating a digital signal.
SNMP agent Software that runs on a managed device such as a server, router, or switch.
SNMP manager (aka: Network Management System (NMS)) Runs a network management application.
socket The combination of the source and destination IP addresses and the source and destination port numbers. Wikipedia
socket pair the source and destination IP addresses and port numbers Wikipedia
Software-Defined Networking (SDN) Began shortly after Sun Microsystems released Java in 1995. Wikipedia
source IP address Contains a 32-bit binary value that represents the source IP address of the packet.
source MAC address Part of an Ethernet frame.
source port The original protocol port that was used in in a data transfer.
Spanning Tree Algorithm (STA) Determines the best paths to the root bridge in the broadcast domain.
Spanning Tree PortFast BPDU Guard Enhancement (aka: BPDU Guard) Feature of the STP enhancement from Cisco that bypasses the spanning tree listening and learning process to speed up network convergence. Cisco
Spanning Tree Protocol (STP) 802.1D A legacy standard that runs all VLANs in a spanning tree instance. Developed to addresses the issue of routing loops. Ensures redundant physical links are loop-free. First standardized by IEEE as 802.1D in 1990. Original algorithm developed by Radia Perlman in 1985. Cisco Wikipedia Cisco (Understanding and Configuring Spanning Tree Protocol)
Spanning Tree Protocol Root Guard Enhancement (aka: root guard) Feature of the STP enhancement from Cisco that lets you administratively pick which bridge should be the root bridge. This works even if another switch is configured with a root priority of 0 and has a lower MAC address. Cisco
SPDY Wikipedia
SPF Tree Created by the SPF algorithm. Used to calculate the best path to each node.
Split Horizon Prevents routing loops in distance vector routing protocols. Does not allow advertisement updates to be sent back down the interface it was learned. Can cause problems for frame relay. Wikipedia
SQL Slammer Worm Worm that exploited a bug in Microsoft SQL Server and Desktop Engine. Launcehed January 25, 2003. Wikipedia
SSH File Transfer Protocol (SFTP) (aka: Secure File Transfer Protocol) Secure file transfer protocol that uses SSH. Wikipedia
SSH forwarding Send another port over SSH.
Standard ACL Permit or deny traffic only from source Layer 3 (IPv4) addresses. Should be placed close to the destination.
Standby Active Virtual Gateway (SVG) Takes over for the AVG if it goes down. Elected by next highest priority to the AVG.
Standby Virtual Forwarder (SVF) When more than 4 gateways are in a GLBP group then the rest will be SVF.
Start of Authority (SOA) Type of DNS record. Wikipedia
startup configuration file Configuration file on network devices that is stored in NVRAM by default and accessed at startup.
stateful protocol Protocol that keeps track of the state of the communication session.
static NAT (aka: one-to-one) Statically configure the mapping of an inside local address (IP of internal server) to an inside global address (IP of server according to the internet). Wikipedia Juniper Cisco
static route Used to connect a specific network or to provide a Gateway of Last Resort. Have an AD of 1. They can be configured with the next-hop IP address (recursive static route), an exit interface (directly connected static route), or both an IP and exit interface (fully specified static route). Static routes are easy to implement in small networks. More secure and efficient than dynamic routes. Routes will always be the same and need to be changed manually as the topology grows/changes. To configure a static route use the syntax:
ip route [destination ip address] [subnet mask] [ exit interface | next-hop ip address ]
Statistical Time-Division Multiplexing (STDM) Uses a variable time slot where data can compete for a free slot. Developed to overcome TDM inefficiency. Wikipedia
Storage Area Network (SAN) Wikipedia
Straight Through Cable (T-568A or T-568B to itself) Most common networking cable. Connect from a host network interface controller (a computer or similar device) to a network switch, hub or router. Wikipedia LINFO
Straight Tip (ST) (aka: stab and twist) Fiber-optic connector that uses a BNC attachment mechanism. Wikipedia
Stream Control Transmission Protocol (SCTP) Transport layer protocol similar to TCP and UDP. Standardized by IETF in RFC 4960 September 2007. RFC 4960 Wikipedia
stub network Router that is connected to a single router. Wikipedia
Stuxnet Worm that targets PLCs. Discovered in June 2010. Wikipedia
subnet ID Part of an IPv6 global unicast address. Organizations use this to identify subnets within a site. Wikipedia
subnet mask (netmask) Logicaly subdivides a network. Identifies what part of an address is the network portion and what is the host portion. Wikipedia
subnet zero The first subnet obtained after subnetting the network address. Wikipedia Cisco
subnetwork (subnet) Logical subdivision of an IP network into two or more smaller networks. Wikipedia
Subscriber Connector (SC) (aka: square connector) Latched fiber-optic connector. Works with either SMF or MMF. Not as popular as ST connectors for LAN connections. Wikipedia
summary route Can help minimize the number of static routes in the routing table. IPv6 addresses can be summarized into a static route if: 1) the destination networks are contiguous and 2) the static routes all use the same exit interface or next-hop IPv6 address. Wikipedia
supernet route A routing table entry with a subnet mask less than the classful mask. (summary address) Wikipedia
switch Network device that typically operates at OSI Layer 2, Layer 3, or Layer 7. Provides centralized connectivity similar to hubs. Forwards data only to the device(s) that need to receive it based on the Layer 2 header. Filters MAC addresses and builds a MAC table. Switch has ports, router has interfaces. Can operate with or without VLANs. First Ethernet switch was introduced by Kalpana in 1990. Wikipedia Network Computing archive
Switch Virtual Interface (SVI) logical interface associated with a VLAN. Can allow for remote switch administration. Used to assign an IP addresses to a Layer 2 switch where no physical interface for IP is available.
Switched Port Analyzer (SPAN) Copies packets to another port on the switch to analyze.
Switched Virtual Circuit (SVC) Established dynamically by sending signaling messages to the network (CALL SETUP, DATA TRANSFER, IDLE, CALL TERMINATION). Netacad
SYN/ACK Packet sent in response to a SYN packet. Wikipedia
Synchronous Code-Division Multiple Access (S-CDMA)
Synchronous Data Link Control (SDLC) Layer 2 protocol. Wikipedia
Synchronous Digital Hierarchy (SDH) European-based ETSI and ITU standard. Uses optical (fiber) to transmit data over a WAN connection. Wikipedia
Synchronous Optical Networking (SONET) ANSI standard. Uses optical (fiber) to transmit data over a WAN connection. (155.52Mbps) Wikipedia
System LifeCycle (SLC) The system lifecycle (SLC) should provide valuable guidance on the best practices that need to be followed throughout the network.
Systems Network Architecture (SNA) IBM's proprietary networking architecture. Created September, 1974. Wikipedia
T1 (aka: T1 Line) Type of dedicated leased line. Composed of 24 64Kbps DS0 channels for a total bandwidth of 1.544Mbps. Originally used for telephony networks to carry one conversation in a single channel. Wikipedia
T3 Line Wikipedia
T568A g.G.o.B.b.O.br.BR Wikipedia Wikipedia
T568B o.O.g.B.b.G.br.BR Wikipedia Wikipedia
tag Helps with the frame election process.
TCP Flag SYN, ACK, FIN, SYN/ACK
TCP Segment Source Port, Destination Port, Sequence Number, Acknowledgement Number, Header length, Reserved, Control bits, Window, Checksum. Urgent, Options, Application Layer Data. Wikipedia
Telecommunications Industry Association (TIA) Wikipedia
Telelocator Alphanumeric Protocol (TAP) Wikipedia
Telenet Commercial packet switched network. Went into service in 1974. Wikipedia
Telnet Protocol used to provide remote CLI access devices such as servers and networking equipment. Does not encrypt transmission. Wikipedia
Test Anything Protocol (TAP) Wikipedia
TEST-NET Addresses Reserved for teaching and learning purposes Wikipedia
tethering Using a smartphone or tablet as a personal hotspot.
three-tier hierarchical design Handles resources efficiently and scales easily.
three-way handshake used by TCP Wikipedia
throughput The maximum amount of data that can be downloaded or uploaded at a time. Wikipedia
Tier 1 ISP Directly connected to the internet backbone. Primarily serves very large companies and Tier 2 ISPs
Tier 2 ISP Primarily serves large companies and Tier 3 ISPs.
Tier 3 ISP Primarily serves small/medium sized companies and homes.
Time Division Multiple Access (TDMA) Wikipedia
Time Division Multiplexing (TDM) Splits the bandwidth of a single link into multiple time slots with a MUX. Wikipedia
tip and ring Red and green wires found in an RJ-11 wall jack, which carry voice, ringing voltage, and signaling information between an analog device (for example, a phone or a modem) and a telephone's wall jack.
topology Layout of a network that describes where devices will go and how they will be connected. There are two kinds of topologies, logical and physical. Wikipedia
traffic classification Categorizes packets automatically based on parameters such as port or protocol. Wikipedia
transceiver Both a transmitter and a receiver. Similar to a repeater. Wikipedia
translation NAT64 allows IPv6 to communicate with IPv4
Transport Control Protocol (TCP) (Layer 4 protocol.) Breaks data into segments for IP before they are sent. Full-duplex. Connection oriented. Has flow-control for each byte stream. TCP segments are marked with flags. Robert Kahn and Vitron Cerf began work on TCP in 1973. Wikipedia Wikipedia (List of Ports)
Transport Control Protocol/Internet Protocol (TCP/IP) (aka: TCP/IP model, Department of Defense (DoD) model) Protocol suite. The IP suite is commonly known as TCP/IP because the foundational protocols in the suite are the Transmission Control Protocol (TCP) and the Internet Protocol (IP).
| 1 | network interface |
| 2 | internet |
| 3 | transport |
| 4 | application |
Transport Layer (OSI Layer 4) Provides transport transfer of data between hosts. Responsible for services such as connection-oriented communication, reliability, flow control, and multiplexing. Layer 4 destination port is used to identify the upper layer protocol. Wikipedia
Transport Layer (OSI Layer 4) Conceptual layer in the internet protocol suite (TCP/IP) and the OSI model. Divides long communications into smaller data packages and handles error recognition and correction. Wikipedia
trap messages Solution to the main disadvantage of SNMP polling. Generated by SNMP agents and sent to the NMS to inform it of events without waiting for it to be polled. Wikipedia
Trivial File Transfer Protocol (TFTP) Used for connectionless active file transfer. Uses port 69. Wikipedia
trunk Single connection between two points such as a switch or branch office. Wikipedia
TrustSec Cisco borderless service. Secures the network based on polices in addition IP/MAC addresses. Different departments can determine who gets access to what while all being spelled out in plain English. YouTube (Cisco - Fundamentals of TrustSec) Cisco YouTube (Cisco - TrustSec Takes the Complexity Out of Network Security)
TUN/TAP Virtual network kernel devices. Wikipedia
Tunnel Mode (aka: IP-in-IP encryption) Secures the entire IP packet. Netacad
Tunneled Direct Link Setup (TDLS) Enables devices to directly connect to each other when connected to the same Wi-Fi network. Wi-Fi Alliance Wikipedia
tunneling Transporting an IPv6 packet over an IPv4 network. IPv6 packet is encapsulated inside an IPv4 packet. (for networks that don't support dual stack) Wikipedia
two-tier hierarchical design Core and distribution layers implemented into a single layer.
Type Length Value (TLV) The data portion of an EIGRP message that is encapsulated in a packet. Wikipedia
Type of Service (ToS) Part of an IPv4 packet header now represented by Differentiated Services Code Point (DSCP). Wikipedia (ToS) Wikipedia (IPv4 Header)
ultimate route Routing table entry that has a next-hop IPv4 address or an exit interface. (Dynamic routes or local routes.)
unequal-cost load balancing Distributes traffic over network interfaces even if they are different distances (metrics). Supported by EIGRP.
unicast (One to One.) Sending a packet from one host to an individual host. Unicast ranges from 0.0.0.0-255.255.255.255 but some address blocks are reserved for other special uses. Wikipedia
Uniform Resource Identifier (URI) Can be a URL or a URN. Wikipedia
Uniform Resource Locator (URL) Wikipedia
Unique Local Address (ULA) These addresses should not be routable in the global IPv6. Unique local addresses are in the range of FC00::/7 to FDFF::/7. Defined in RFC 4193 October, 2005. Wikipedia RFC 4193
Universal Mobile Telecommunications System (UMTS) Third generation mobile cellular system for networks based on the GSM standard. Wikipedia
Unshielded Twisted Pair (UTP) Cable found in many Ethernet networks and telephone systems. terminated with an RJ connector, Usually RJ-45 (8P8C) or RJ-11 (6P2C). TIA/EIA-568 is the standard for wire color codes to the pinouts for Ethernet cables.
up/down status up/protocol down. Layer 2 issue: (keepalive, encapsulation, clocking)
uplink port The port used for internet connectivity.
User Datagram Protocol (UDP) Layer 4 connectionless protocol that has unreliable delivery. (Does not acknowledge if the data is received.) Uses less overhead than TCP. Wikipedia
V.35 Operates at Layer 1. Standard for modems. Wikipedia ITU
V.92 ITU standard for 56 kb/s download and 48 kb/s upload modems. Introduced August 1999. Wikipedia ITU
Variable Length Subnet Mask (VLSM) (classless subnetting) Helps avoid wasting IP addresses when subnetting a network. Wikipedia
Version Contains a 4-bit binary value identifying the IP packet version. For IPv4 packets, this field is always set to 0100.
Very Small Aperture Terminal (VSAT) Creates a private WAN for connectivity to remote locations. Wikipedia
Virtual Circuit (VC) Two kinds of VCs: Switched Virtual Circuits (SVCs) and Wikipedia
Virtual Local-Area Network (VLAN) (aka: Virtual LAN) Similar to a regular LAN. Logical broadcast domain that can split physical LANs. Allows different security policies to be applied to different hosts. Wikipedia Cisco
Virtual Router Redundancy Protocol (VRRP) IETF open standard that operates almost identically to HSRP from Cisco Wikipedia
Virtual Teletype (VTY) telnet Wikipedia
VLAN Double-Tagging Embeds a 802.1Q tag inside a frame allowing it to go to another VLAN. Because most switches only perform one level of decapsulation, the receiving switch only looks at the inner 802.1Q tag. (Outer tag would be the native VLAN).
Voice over Asynchronous Transfer Mode (VoATM) Wikipedia
Voice over IP (VoIP) Requires no more than 150ms one-way delay, no more that 30ms of jitter, and no more thatn 1 percent packet loss. Wikipedia
voice traffic Maximum recommended one-way delay is 150ms for voice.
VoIP Server (aka: IP PBX) An example VoIP server is Asterisk.
VTY password Password used on a to secure a Telnet or SSH connection. Cisco
WAN Interface Card (WIC) Wikipedia Cisco
WAN Switch Cisco
wavelength multiplexing Fame encoding technique used in fiber optic media.
Wavelength-Division Multiplexing (WDM) Technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. Wikipedia
Weave Communications layer for IoT devices. Developed by Google. Announced May 28, 2015. Website Ars Technica
whois Used to lookup domain name information. Wikipedia ICANN RFC 3912
Wi-Fi A WLAN technology. Uses the CSMA/CA media access process. Supposedly the name Wi-Fi is a play on words for Hi-Fi. Wikipedia
Wi-Fi Protected Access (WPA) Wikipedia
Wi-Fi Protected Access II (WPA2) (aka: 802.11i) Includes mandatory support for CCMP, an AES encryption. Replaced WPA. Required for all new devices to bear the Wi-Fi trademark starting March 13, 2006. Wikipedia
Wi-Fi Protected Access III (WPA3) Uses 192-bit encryption and individualized encryption for each user. Announced as a replacement to WPA2 by the Wi-Fi Alliance January 2018. Wikipedia
Wide Area Application Services (WAAS)
Wide Area Network (WAN) Network that spans a large geographical area such as multiple buildings far apart on a campus. Uses mostly OSI layers 1 and 2. Connections are typically leased out by a service provider. Wikipedia
window size The amount of data that a source can transmit before an acknowledgement must be received. One of the fields in the TCP header that enables the management of lost data and flow control. Wikipedia
Wired Equivalent Privacy (WEP) (deprecated) Uses the RC4 stream cipher for confidentiality, and the CRC-32 checksum for integrity. Can be easily hacked. Introduced as part of the original 802.11 standard ratified in 1997. Superseded by Wi-Fi Protected Access (WPA) in 2003. Deprecated in 2004. Wikipedia
Wireless Access Point (WAP) Wikipedia
Wireless ad hoc network (WANET) A wireless LAN topology. When two or more devices are directly connected through a wireless network without extra infrastructure. Wikipedia
Wireless Internet Service Provider (WISP)
Wireless LAN (WLAN) A LAN that uses radio waves to transmit data. Use the older CSMA/CA to decide when to gain access to the wireless media. Three main categories: IBSS, BSS, and ESS. Wikipedia
WLAN coverage Recommended amount of coverage overlap in a 2.4GHz WLAN is 10-15% to prevent connections from dropping when roaming between coverage cells. Use nonoverlapping channels for adjacent cells.
work area The outlets that connect to hosts through horizontal cabling. Two outlets should be provided at the wall plate; one for voice and one for data. Wikipedia
World Wide Web (WWW) (aka: the Web, port 80) HTTP/web services. Information space where documents and other web resources are identified by Uniform Resource Locators (URLs, such as https://www.example.com/), which may be interlinked by hypertext, and are accessible via the Internet. The resources of the WWW may be accessed by users via a software application called a web browser. Invented by English scientist Tim Berners-Lee while working for CERN by submitting Information Management: A Proposal on March 12, 1989. Wikipedia
Worldwide Interoperability for Microwave Access (WiMAX) Wikipedia
worm Malicious code that replicates itself. Responsible for some of the most devastating attacks on the internet. Primarily network based and can slow networks down. Can run on its own without user interaction. Tend to exploit software vulnerabilities.
| Three major parts: |
|---|
| enabling vulnerability |
| propagation mechanism |
| payload |
X-Lite Free VoIP softphone Website
X.25 ITU-T standard protocol suite for packet switched wide area network (WAN) communication. Published in "The Orange Book" in 1976. Wikipedia
X.509 ITU-T standard for Public Key Infrastructure (PKI). Released July 3, 1988. Wikipedia ITU
Yagi antenna Directional antenna used for long distances. Wikipedia
ZeroAccess Trojan horse that connects to a botnet. Wikipedia
Zeus Trojan horse. First identified July 2007. Wikipedia
zone file Text file containing DNS records for a domain name.