2010 ALL NEW TRICKS

A routing protocol is used on a router which allows different computer networks to communicate with each other [By default a Network i.e.set of computers with ip address of same class can not communicate with network of diff ip address ]

Some of the most popular and commonly used routing protocols are:-
~!~ Open Shortest Path First (OSPF)
~!~ Routing Information Protocol (RIP)
~!~ Interior Gateway Routing Protocol (IGRP)
~!~ Enhanced Interior Gateway Routing Protocol (EIGRP)
~!~ Border Gateway Protocol (BGP)

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Routing Information Protocol (RIP) is one of the most commonly used routing protocol as it is non proprietary. It is a type of Interior Gateway distance-vector routing protocol employing the hop count as a routing metric. The maximum number of hops allowed with RIP is 15. The default update interval of RIP configured router is 30 seconds which results in large amount of network traffic. RIP runs above the network layer and uses UDP port 520 to transmit its updates. To avoid routing loops a technique called Split Horizon with Poison Reverse is used.

There are two version of RIP, RIPv1 and RIPv2.

RIPv1 uses classful routing and does not support VLSM (Variable Length Subnet Mask). This means that the internal subnets within the same network must be of same size and lack of authentication does not make it the first choice for networks.

RIPv2 was developed to overcome the limitations imposed by RIPv1 and as a result of new development, the RIPv2 supported classless Inter-Domain routing and VLSM. But the limitation of 15 hop count still remained.


Interior Gateway Routing Protocol (IGRP) is a proprietary distance-vector routing protocol invented by Cisco, used by routers to exchange routing data within an autonomous system.

IGRP was created in part to overcome the limitations of RIP (maximum hop count, and a single routing metric) when used within large networks. IGRP supports multiple metrics for each route, including bandwidth, load, delay, and relability; to compare two routes these metrics are combined together into a single metric, using a formula which can be adjusted through the use of pre-set constants. The maximum hop count of IGRP-routed packets is 255.

Its successor is EIGRP, an advanced distance-vector routing protocol, that uses many features of link-state protocols, and adds Diffusing Update Algorithm (DUAL) ideas to the basic distance-vector mechanism of IGRP.



Enhanced Interior Gateway Routing Protocol(EIGRP) is a Cisco proprietary routing protocol based on their original IGRP. EIGRP is a distance vector routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and processing power in the router.

Some of the routing optimizations are based on the Diffusing Update Algorithm (DUAL) work from SRI, which guarantees loop-free operation. The maximum hop count of EIGRP-routed packets is 224.

The data EIGRP collects is stored in three tables:
1.Neighbor Table
2.Topology Table
3.Routing table


Open Shortest Path First (OSPF) is a  non proprietary Open standerd link state Interior Gateway Routing protocol (IGRP). It uses cost as its routing metric.

Some of the features of OSPF are:-
Support for MD5 based authentication
Support for VLSM - Variable Length Subnet Mask (classless routing)
Tagging of routes

OSPF based network can contain multiple smaller networks. OSPF uses both unicast and multicast for link state updates. Multicast address of 224.0.0.5 and 224.0.0.6 are used to send updates to other routers.



Border Gateway Protocol (BGP) It is core routing protocols in the Internet and works by maintaining a table of IP networks or ‘prefixes’ which designate network reachability between autonomous systems (AS). It is described as a path vector protocol. BGP does not use technical metrics, but makes routing decisions based on network policies or rules. The current version of BGP, BGP version 4.

BGP supports classless interdomain routing and uses route aggregation to decrease the size of routing tables. Very large private IP networks can also make use of BGP; an example would be the joining of a number of large OSPF networks where OSPF by itself would not scale to size. Another reason to use BGP would be multihoming a network for better redundancy. All Internet service providers must use BGP to establish routing between one another, it is one of the most important protocols of the Internet.

When BGP is running inside an AS, it is referred to as Internal BGP (IBGP Interior Border Gateway Protocol). When BGP runs between autonomous systems, it is called External BGP (EBGP Exterior Border Gateway Protocol).