Broadacst network - link state change updates

In case of point to point networks when link goes down, the attached router will come to know about the state change and will immediately flood the link state update packets. So in this case it takes less time for the state change to get propagated.

R1 R2 R3 R4 | | | | | | | |

------------------ Multiaccess network

How does this work in case of broadcast networks. Support router R1,R2,R3 and R4 are part of broadcast networks and R1,R2 are DR and BDR respectively. If the link connecting R3 to broadcast network is down how will the DR come to know about this state change and how long does it take to come to know this change.

As I understand it is possible to come to know about this state change using hello packet.Does DR wait for DeadInterval and then declare that the state change. In that case it is long interval.

Any help on this...



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Yes, DR waits for DeadInterval to expire so it could declare the neighbor dead. It can be a long time, but you can always tweak the timers to get better response.

Reply to
Ivan Ostreš

only if the physical layer fails so you get a state transition on the port - for example some ethernet links between sites get hooked to switches so the router can tell when the WAN is down.


timeout of the adjacency between the DR and other router (the BDR should also notice as its session goes down)

Yes - but you can alter the timers to reduce that - but you need the dead time to be a multiple of the hello time the standards docs explain the constraints.

i believe that IS-IS can be set up to time out more quickly than OSPF, since the hello timer can be sub 1 sec - Cisco were talking about a similar optional setting in OSPF but i dont know if it ever got implemented.

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