Interesting find with VRRP

Answered Question
Sep 23rd, 2009

All,

I'm using VRRP in GNS, and I noticed something. I've got the following:

RTRA:

int fa0/1

ip address 10.125.95.1

vrrp 1 track 1

vrrp 1 priority 110

vrrp 1 ip 10.125.95.1

RTRB:

ip address 10.125.95.3

vrrp 1 ip 10.125.95.1

If I track the serial interface on RTRA in the VRRP group, and the serial interface goes down, with the ip address set the same as the virtual address, the group doesn't move over. If I set the physical ip address to .2 instead of .1, and I leave the virtual at .1, the tracking works and the group moves over.

I'm wondering why it matters which address I have on the interface if I'm tracking a different interface.

Thanks,

John

I have this problem too.
0 votes
Correct Answer by Peter Paluch about 7 years 2 months ago

John,

This is probably due to the VRRP RFC 3768 statement in section 5.3.4: The priority value for the VRRP router that owns the IP address(es) associated with the virtual router MUST be 255 (decimal). As the RTRA is the owner of the virtual router IP address (its real IP address is the same as the VRRP group's IP address), its priority is, according to the RFC, 255. The command "vrrp priority" seems to be ignored here, and/or the tracking does not influence the priority of the router - I haven't tried it myself but this is my general idea about it.

Test it and have a look at the priorities displayed in the show vrrp outputs with the tracked interface being up and down. I believe that this is the way to go for finding out what's going on.

Best regards,

Peter

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Correct Answer
Peter Paluch Wed, 09/23/2009 - 09:20

John,

This is probably due to the VRRP RFC 3768 statement in section 5.3.4: The priority value for the VRRP router that owns the IP address(es) associated with the virtual router MUST be 255 (decimal). As the RTRA is the owner of the virtual router IP address (its real IP address is the same as the VRRP group's IP address), its priority is, according to the RFC, 255. The command "vrrp priority" seems to be ignored here, and/or the tracking does not influence the priority of the router - I haven't tried it myself but this is my general idea about it.

Test it and have a look at the priorities displayed in the show vrrp outputs with the tracked interface being up and down. I believe that this is the way to go for finding out what's going on.

Best regards,

Peter

Peter Paluch Wed, 09/23/2009 - 10:11

Simon,

Thank you very much for confirming my suspicion!

Best regards,

Peter

John Blakley Wed, 09/23/2009 - 09:28

Peter,

You're 100% correct. The priority is 255, but I thought when tracking, the priority of the non-tracked interface wouldn't matter. Apparently it does though.

Thanks,

John

Peter Paluch Wed, 09/23/2009 - 10:12

John,

You are heartily welcome. I have also learned something new, thanks to you and Simon. Thanks!

Best regards,

Peter

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