IS-IS DIS hello

Unanswered Question
Dec 17th, 2007


IS-IS DIS sends hellos at 3.3 seconds, so does it means 3.3 seconds between DIS and all other routers as well as other routers also send hellos to DIS at the same seconds...

and IS-IS normall routers are exchanging hellos between them at 10 sec... is that correct?

so in short:

Hellos between DIS and ALl other is 3.3

Hellos between ALLother routers is 10 Seconds



I have this problem too.
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royalblues Mon, 12/17/2007 - 12:15


your understanding is correct

In IS-IS all routers in a lAN establish adjacencies with eacjh other unlike OSPF where the adjacency is built only with the DR and the BDR.

IN IS-IS, the routers send IIHs to maintain adjacency and by default this is at 10 seconds. The DIS on the other hand sends the hello every 3.3s which is 3 times faster than for other routers. This is mainly done to quickly detect DIS failures as IS-IS does not have a backup DIS




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