[c-nsp] HSRP to VRRP migration

[Matt Addison]

On Wednesday, March 11, 2015, Cydon Satyr <cydonsatyr at gmail.com> wrote:

> Hello guys. We have a bunch of redundant router Cisco pair routers, that
> are running HSRP, that needs to be migrated to VRRP.
>
> The question is, could this be down with 0 downtime?
>
> My guess is, if we replace backup HSRP router to run VRRP master, then
> gratious-arp war could start, with both routers trying to send proper mac
> address info to LAN. I guess with some filter hosts could be convinced to
> use VRRP's mac address... or something.
>
> I understand  a proper maintenance window should be ordered, but, could
> this be done with no downtime (or at least near 0, just so hosts update arp
> table)? Any ideas?
>

Assuming your platform lets you configure HSRP and VRRP simultaneously on
the same interface, change the HSRP address to a new address, then set up a
new VRRP group on a different group number for the original IP.  Any ARPs
before you get the new group established will go unanswered, but other
traffic should work as normal as the router will still receive and
route datagrams destined to the HSRP group MAC.

And like Nick said, whatever you do, lab it first.

~Matt