[AusNOG] Vrrp

[David Hill]

Hi Rhys,

Has anyone had much experience with using Vrrp on a Mikrotik?

I use Juniper gear, so apologies if I’m overlooking some Mikrotik-specific VRRP extensions, etc…

It seemed pretty easy to setup but the manual said the floating IP must be a /32 and to put an IP on the physical interface with a /24
This seemed wrong so I just put a /24 on the Vrrp interface and a completely different subnet on the physical interface for the routers to communicate.

VRRP requires that the VIP and interface IP’s be in the same subnet so the MAC address associated with the VIP can be updated via gratuitous ARP. So you do ‘waste’ two IP’s per subnet (assuming two routers).  It doesn’t need to be a /24 though - /29 or greater is sufficient.


Thinking I was clever all was well till about 1am two days after I did this, then it completely failed, switching back and forth from master to backup, basically having two masters on and off.

Is having a /32 on the vrrp really necessary, if so why?

Yes. It is used for outbound traffic for client devices in the subnet. Inbound traffic can traverse both master and slave devices.

Why would it have been all good for two days?

I highly doubt that it was.

So my config that lasted two days
Vrrp 192.168.1.1/24 (floating IP I care about)
Physical 10.0.1.1/24  (to communicate with master/backup routers)

See above.

How the manual says to do it
Vrrp 192.168.1.1/32
Physical 192.168.1.2/24

That’s the correct configuration - As I mentioned above, VRRP doesn’t mandate a /24 subnet on the interface though.

Doing it the second way will mean a lot more IP’s/config as I want to have around 20 floating IP’s

Why? Take a look into MC-LAG - No idea if your gear supports this, but it sounds a better fit for how you’re trying to build your network.

Kind Regards,

David Hill
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