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odge
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Joined: Mon Nov 29, 2010 2:53 pm

VRRP with /30

Fri Mar 14, 2014 1:39 am

I want to setup VRRP at a customer site, but at this site the ISP has only supplied a single /30 address for customer equipment.

It seems to work if I use a /29 subnet, and make fake addresses, (obviously I'll never be able to contact those other 3 real addresses- but I dont care).

The only problem is how do I force the mikrotik never to try send any packets to the gateway using the fake address (which the gateway will never respond on).
 
joegoldman
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Re: VRRP with /30

Sat Mar 15, 2014 10:37 pm

What i've found the best thing to do is use private IP address' (10.x.x.x/172.16.x.x/192.168.x.x etc) for VRRP, then use the On Master and On Backup script execution to make changes to your IP addressing as required.
 
odge
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Re: VRRP with /30

Mon Mar 17, 2014 12:11 pm

ok, thats an interesting method.

do you have a sample of the method you use (do you just enable and disable addresses?)

As it turned out, just borrowing the IP and using /29 instead of /30 works (except obviously I cant route to the real IPs of those anymore, but its ok, these are generally only used for routing on our ISPs network.

I did see a issue at a point when NATing went out on one of the fake addresses, but it doesn't seem to be an issue anymore. I added a src NAT rule, saying unless it was for the VRRP addresses, always srcnat the fake IP back to the real IP (which is the VRRP), I'm not sure if thats the reason it works, but I've not seen any fake address on it since, and I can move it back and forth between routers no problem.

Have you encountered the bad checksum issue before... I often seem to have to use version 2 of vrrp and get checksum errors on version 3.

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