Getting CARP to broadcast on a different interface

[Matthew Grooms]

Hi Niklaas,

Rewriting the multicast destination would be a neat trick, but sadly no. 
You can't rewrite a destination address on egress. Using a route-to rule 
would only modify the destination MAC address. If you were using 
OpenBSD, you would switch from multicast to unicast using the syncpeer 
option. Unfortunately that's not supported on FreeBSD.

At one point I wrote a broadcast relay daemon to forward select UDP 
broadcast traffic between two networks separated by an IPsec tunnel. It 
had limited utility, but it worked well for what I needed it to do. I 
wonder if someone has written a multicast relay daemon that works in a 
similar fashion. If so, you could use it to forward CARP traffic to a 
peer. Super ugly, but it would probably do the trick in this scenario.

-Matthew

On 6/8/2016 9:56 AM, Niklaas Baudet von Gersdorff wrote:
> Trond Endrestøl [2016-06-08 15:53 +0200] :
>
>> Although it sounds pretty bad, you could set up CARP on the internal
>> network and use those CARP events to control the main interfaces, e.g.
>> re-adjust their annoncement intervals, or something equally awful.
>
> Thanks, Trond. As you said, not that it sounds like a good idea but it's
> a solution I will think about.
>
> What also came up in my head: Can't I re-reroute the CARP packets with
> pf somehow?
>
>     Niklaas
>