Routing protocols

Routing protocol

What is a routing a routing protocol? Why we rely so much on them? A Routing protocol tells the routers how communicate with each other, how to distributing information (routing info) that enables them to select routes between any two nodes on a computer network. Routing algorithms determine the specific choice of route. Each router has a prior knowledge only of networks attached to it directly (physical, on it’s Ethernet interface for example). A routing protocol shares this info first among immediate neighbors, and then throughout the network. This way, routers gain knowledge of the topology of the network.

The specific characteristics of routing protocols include the manner in which they avoid routing loops, the manner in which they select preferred routes (like using information about hop costs), the time they require to reach routing convergence, their scalability, and other factors.

The three major classes are in widespread use on IP networks:

  • Interior gateway protocols type 1, link-state routing protocols, such as OSPF and IS-IS
  • Interior gateway protocols type 2, distance-vector routing protocols, such as Routing Information Protocol, RIPv2, IGRP.
  • Exterior gateway protocols are routing protocols used on the Internet for exchanging routing information between Autonomous Systems, such as Border Gateway Protocol (BGP), Path Vector Routing Protocol. Exterior gateway protocols should not be confused with Exterior Gateway Protocol (EGP), an obsolete routing protocol.

OSI layer designation

Routing protocols, according to the OSI routing framework, are layer management protocols for the network layer, regardless of their transport mechanism:

  • IS-IS runs on the data link layer (Layer 2).
  • Open Shortest Path First (OSPF) is encapsulated in IP, but runs only on the IPv4 subnet, while the IPv6 version runs on the link using only link-local addressing.
  • IGRP, and EIGRP are directly encapsulated in IP. EIGRP uses its own reliable transmission mechanism, while IGRP assumed an unreliable transport.
  • Routing Information Protocol (RIP) runs over the User Datagram Protocol (UDP). Version 1 operates in broadcast mode, while version 2 uses multicast addressing.
  • BGP runs over the Transmission Control Protocol (TCP).

Interior gateway protocols

Interior gateway protocols (IGPs) exchange routing information within a single routing domain. Examples of IGPs include:

  • Open Shortest Path First (OSPF)
  • Routing Information Protocol (RIP)
  • Intermediate System to Intermediate System (IS-IS)
  • Enhanced Interior Gateway Routing Protocol (EIGRP)

Exterior gateway protocols

Exterior gateway protocols exchange routing information between autonomous systems (AS). Examples are:

  • Exterior Gateway Protocol (EGP)
  • Border Gateway Protocol (BGP)

Routing software

There are many software editions for most of the common routing protocols. Examples of open-source applications are Bird Internet routing daemon, Quagga, GNU Zebra, OpenBGPD, OpenOSPFD, and XORP.

Routed protocols

A routed protocol is used to deliver application traffic because It provides addressing information in its Internet layer (network layer). This allows a packet to be forwarded between the network. Examples of routed protocols are the Internet Protocol (IP) and Internetwork Packet Exchange (IPX).