OSPF unicast Hello Packet on ethernet

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May 9th, 2011
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hello,


i can always capture unicast hello packet on ethernet link between two router at Init stage, without any configuration of network type. After that all hello packets are multicasted normally. Did anybody know the reason?


thanks


Syrinx

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Giuseppe Larosa Mon, 05/09/2011 - 08:48
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Hello Syrinx,


during extart/exchange and loading phase unicast packets are used to build the OSPF adjacency


an OSPF adjacency is always between a pair of OSPF routers that have reached two way status.


typically a new router forms OSPF neighborships with all routers on subnet, but only two OSPF adjacencies with OSPF DR and OSPF BDR


for this reason communication becomes unicast in those phases: only two nodes are involved in the process.


Edit:


on the routers you can use


debug ip ospf adjacency


to see the process


Hope to help

Giuseppe

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