Showing results for 
Search instead for 
Did you mean: 

IS-IS hello interval timer in P2P

Level 1
Level 1

I'm doing a lab research where for the same topology I have a configuration for the IS-IS point-to-point and OSPF point-to-point protocols. I measure the network convergence time (not in the event of a failure, but in what time from the moment of starting the network the convergence is achieved, of course, excluding the times of starting the router) and the lower time results are achieved by IS-IS. I was wondering where the difference between the protocols came from, because to my knowledge the times should be similar for both. I caught packets with Wireshark and you can see the difference between the protocols, but according to the literature, it shouldn't be there. In OSPF, the first Hello packet from R1 to R2 is sent in about 1 second, then immediately the Hello packet from R2 to R1 is sent. A Hello packet containing R2's RID is sent from R1 after approximately 10 seconds, which is according to the default interval. In IS-IS, however, this exchange occurs without the 10 second interval (which is also set to 10 seconds by default), instead another Hello packet containing the ID is sent after about 2-4 seconds. I know this value can be reached for Hello packets for DIS, but the network is set as point-to-point so there is no DIS router. I am working on Cisco routers, both of these timers default to 10 seconds. I don't understand why IS-IS sends these packets so fast, I didn't change the timer settings. I'm adding sample files from Wireshark for both protocols.

Edit: I forgot to mention that after establishing the connection between the routers, the Hello packet interval is as assumed to be 10 seconds.

2 Replies 2


are you doing this test on real, live routers, or on simulated devices (such as GNS3) ?

I'm testing in the GNS3 on Cisco CSR 1000v routers.

Review Cisco Networking for a $25 gift card