[c-nsp] HSRP to VRRP migration

[Phil Mayers]

On 11/03/15 23:51, Nick Hilliard wrote:
> On 11/03/2015 23:41, Cydon Satyr wrote:
>> 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?
>
> Have you labbed this up?
>
> You haven't, because you haven't yet run into the problem that you cannot
> send a gratuitous ARP using e.g. ping on the VRRP virtual IP address.  The

You can't do this with zero outage, but does VRRP not send a g-arp when 
it becomes active on IOS?

If so, this might work

1. Shutdown hsrp slave
2. Configure VRRP group with fake IP, very short timers
3. "no standby" followed by "vrrp ..." to give it a real IP

The main risk is the g-arp being dropped/missed. It's a shame the 
masters don't send several, spaced at $hello_timer interval or 
something. This is a problem with changing HSRP group number too.

But it all depends if IOS VRRP will send a g-arp on "active"....