Chapter 3- Fundamentals of WANs and IP Routing

Address Resolution Protocol (ARP)

An Internet protocol used to map an IP address to a MAC address.

• Defined in RFC 826.

Default router (default gateway)

On an IP host, the IP address of some router to which the host sends packets when the packet's destination address is on a subnet other than the local subnet.

Domain Name System (DNS)

An application layer protocol used throughout the Internet for translating hostnames into their associated IP addresses.

Ethernet Line Service (E-Line)

A specific carrier/metro Ethernet service defined by MEF (MEF.net) that provides a point-to-point topology between two customer devices, much as if the two devices were connected using an Ethernet crossover cable.

• One term used to describe Ethernet WAN link

Ethernet WAN

A general and informal term for any WAN service that uses Ethernet links as the access link between the customer and the service provider.

High-Level Data Link Control (HDLC)

A bit-oriented synchronous data-link layer protocol developed by the International Organization for Standardization (ISO).

Hostname

The alphanumeric name of an IP host.

IP address

In IP version 4 (IPv4), a 32-bit address assigned to hosts using TCP/IP.

• Each address consists of a network number, an optional subnetwork number, and a host number.

• The network and subnetwork numbers together are used for routing, and the host number is used to address an individual host within the network or subnetwork.

IP network

An IPv4 Class A, B, or C network called a classful network because these networks are defined by the class rules for IPv4 addressing.

IP packet

An IP header, followed by the data encapsulated after the IP header, but specifically not including any headers and trailers for layers below the network layer.

IP subnet

TCP/IP groups IP addresses together so the ones in the same physical network are in the same group

• Similar to zip codes

Leased line

A serial communications circuit between two points, provided by some service provider, typically a telephone company (telco).

• Because the telco does not sell a physical cable between the two endpoints, instead charging a monthly fee for the ability to send bits between the two sites, the service is considered to be a leased service.

Ping

An Internet Control Message Protocol (ICMP) echo message and its reply.

• Tests basic network connectivity, without relying on functioning applications

Routing protocol

A set of messages and processes with which routers can exchange information about routes to reach subnets in a particular network.

• Examples of routing protocols include Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).

Routing table

A list of routes in a router, with each route listing the destination subnet and mask, the router interface out which to forward packets destined to that subnet, and as needed, the next-hop router's IP address.

Serial interface

A type of interface on a router, used to connect to some types of WAN links, particularly leased lines and Frame Relay access links.

Subnetting

The process of subdividing a Class A, B, or C network into smaller groups called subnets.

Telco

A common abbreviation for telephone company.

Wide-area network (WAN)

A part of a larger network that implements mostly OSI Layer 1 and 2 technology, connects sites that typically sit far apart, and uses a business model in which a consumer (individual or business) must lease the WAN from a service provider (often a telco).