In determining the best route to a destination, different routing protocols use a number of different measurements. These measurements are called metrics. Each routing protocol uses one or more metric to calculate the best route to a particular destination. The most common metrics include path length (hop count), reliability, delay, bandwidth, load, and financial cost of a link.

Another major difference between routing protocols is how they handle updating each other with current information. There are many methods of doing this. Given these major differences, routing protocols are broken into two main categories: Distance Vector and Link State.

Distance Vector protocols include RIP and IGRP. They send their entire routing tables out in all directions at regularly scheduled intervals.
Link State protocols are more advanced than distance vector protocols because, unlike distance vector, they do not send periodic routing updates. Link State protocols include OSPF, NLSP, BGP, and IS-IS.They send partial routing tables (of their own networks) to everyone and then send updates when necessary.

RIP (Routing Information Protocol)

RIP is a true distance vector routing protocol. It sends the complete routing table out to all other active interfaces every 30 seconds. RIP uses Hop Count as it’s only metric. The maximum number of hops in a RIP network is 15, one hop is a directly connected network, and 16 hops is an unreachable network.

1. RIP v1 uses only classful routing. RIP v2 uses classless routing.

RIP uses three different kinds of timers to regulate its performance:

Route Update timer sets the interval (30 seconds) between periodic routing updates in which the routers sends a complete copy of its routing table out to all neighbors.
Route Invalid timer determines the length of time that must expire (90 seconds) before a router determines that a route has become invalid.
Router Flush timer sets that time between a route becoming invalid and its remove from the routing table (240 seconds).

RIP Configurations
RIP is very simple to configure. All you need to do is enable RIP and add each network that uses RIP. However, RIPv2 has a few more possible commands; you can use two of them: version and no auto-summary.

Because the router will by default use RIPv1, you must use the version command to tell the router to use RIPv2. In addition, by default RIPv2 will summarize major networks across boundaries. Use the no auto-summary command to stop summarization.

Monitoring and Verifying RIP

IGRP (Interior Gateway Routing Protocol)

The Interior Gateway Routing Protocol (IGRP) is a Cisco proprietary protocol. Like RIP, IGRP is a distance-vector interior routing protocol. However, unlike RIP, IGRP can be used in larger autonomous systems due to its large maximum hop-count limit of 255, compared to RIP’s maximum hop count of 16.

IGRP uses bandwidth and delay of the line by default as metric for determining the best route to an internetwork. This is called a composite metric. Reliability, load and maximum transmission unit (MTU) can also be used, although they are not used by default.

To control performance IGRP uses different kind of timers:

Update Timers specifies how frequently IGRP routing messages will be sent. The default is 90 seconds.
Invalid Timer specifies how long a router should wait in the absence of a routing-update message of a specific route before declaring it invalid. The default is three times the Update timer, 270 seconds.
Holddown Timer specifies the holddown period. The default is three times the update timer plus 10 seconds, 280 seconds.
Flush Timer indicates how much time should pass before an IGRP route is flushed from the routing table. The default is seven times the routing update period, 630 seconds.

IGRP Configurations

Monitoring and Verifying IGRP