Difference between OSPF and IS-IS

Asked By 10 points N/A Posted on -

Good day!

I'm currently studying CISCO 2 right now and so far, I only have a few knowledge on OSPF protocol.

I've been wondering what the IS-IS protocol has that is not found in the OSPF protocol.

What is the difference between these two routing protocols?

Answered By 0 points N/A #100316

Difference between OSPF and IS-IS


Hi Mr. Alvaldez,

OSPF routers can fit in to numerous areas and can sustain virtual links. IS-IS routers, on the other hand,  fit in to exactly one area and cannot sustain virtual links since it rides L2 directly.

IS-IS Routes calculated involving L2 to L2 routes in IS-IS are link-state / SPF computation. L1 routers have no straight outer area connection.  OSPF Like routes (non-local) inside OSPF are distance vector computation.

OSPF sustains NBMA as well as point-to-multipoint links. On the other hand, IS-IS is not capable to sustain these.

IS-IS traverses openly over layer two, against on IP akin to OSPF, which might propose a security gain (IS-IS hits can’t be routed).

OSPF opts for a DR and BDR that can’t be pre-empted, for the broadcast networks. While IS-IS opts for just a single DIS that may be pre-empted.

OSPF assigns area 0, which is a backbone area, for advertisements within an area; while IS-IS systematizes the domain into two layers.


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