Thursday, August 16, 2012

Distance vector protocols and their issue of looping

Distance vector Routing Protocols send entire table at specific intervals

Distance vector protols are simple to implement but they have looping issues,count down to infinity issue

There are 5 loop prevention mechanism in Cisco Routers

1.Maximum Distances(For RIP it is 16 hops,if any network is 16 hops away it's not considered anymore,)

2.Route Poisoning(advertise that the network is down immediately,they kill the network by sending the network a maximum hop count bigger than 16 so that the maximum distance law takes the network out)

3.Triggered Updates(send the update immediately rather than waiting 30 sec like RIP generally does,poison the route,and tell the neighbour device that the network is down,triggered idea should be avoided in an unstable network where interfaces are going up and down)

4.Split Horizon(tell routers do not send updates/advertisements in the same direction you recieved them)

5.Hold Down Timer(it won't believe any other updates about a particular route for a cirtain amount of time,180 sec is typical,works great in a situation where interfaces are going up and down)

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