Day 11 & 12 : Distance Vector Routing Protocols

RIP, RIPv2 and IGRP are distance vector routing protocols.
DV routing protocols use hop count (except IGRP) as the metric to find the best path.

DV routing protocols advertise the whole routing table to the adjacent neighbors as periodic updates.

DV routing protocols do not send subnet mask in routing updates and uses default subnet mask based on IP address class. That is why they are know as classful routing protocols.
* RIPv2 does send subnet mask in routing updates and hence it is a classless routing protocol.

DV routing protocols are subject to routing loops.

DV routing protocols have very slow network convergence time.

Maximum hop count is used to limit the size of the network. (RIP uses 15 as maximum, IGRP as 255)

Due to periodic nature of DV routing protocols, there are several timers.
1. Update timer (time between successive routing updates)
2. Hold timer (time that a router keeps a route without routing updates from neighbor)
3. Flush timer (time that a router keeps before a router deletes the route)

RIP - 30/180/240 (same for RIPv2)
IGRP - 90/280/630

Routing Loop Prevention in DV Routing Protocols
1. Split Horizon (do not advertise a route back to the incoming interface)
2. Triggered update (sends a routing update as soon as the router detects a link failure)
3. Route Poisoning (send a route with metric of 16 when a router detects a route failure)
4. Poison Reverse (split horizon update with route poisoning)