UCARP Behind NAT

[Chris Snyder <chris@keyedupmedia.com>]

Hey Guys,

First time here on the list, so hopefully I get everything right here.

I have two Squeeze systems that I have setup with UCARP for auto-failover.

Here's the relevant /etc/network/interfaces of Server 1:

 10 iface eth0 inet static
 11         address 192.168.1.21
 12         netmask 255.255.255.0
 13         gateway 192.168.1.1
 14         dns-nameservers 8.8.8.8 8.8.4.4
 15
 16         # UCARP
 17         ucarp-vid 3
 18         ucarp-vip 192.168.1.20
 19         ucarp-password [pass-here]
 20         ucarp-advskew 100
 21         ucarp-advbase 1
 22         ucarp-master no
 23
 24
 25 iface eth0:ucarp inet static
 26         address 192.168.1.20
 27         netmask 255.255.255.255


And /etc/network/interfaces of Server 2:


 10 iface eth0 inet static
 11         address 192.168.1.22
 12         netmask 255.255.255.0
 13         gateway 192.168.1.1
 14         dns-nameservers 8.8.8.8 8.8.4.4
 15
 16         # UCARP
 17         ucarp-vid 3
 18         ucarp-vip 192.168.1.20
 19         ucarp-password [pass-here]
 20         ucarp-advskew 100
 21         ucarp-advbase 1
 22         ucarp-master no
 23
 24 iface eth0:ucarp inet static
 25         address 192.168.1.20
 26         netmask 255.255.255.255

Now this setup works great on the LAN. I can access 192.168.1.20 fine
while pulling the Ethernet cables from either server. The problem is
that I'm trying to forward an external IP to 192.168.1.20 through a
NAT.

It forwards fine when both machines first come up and Server 1 is
dominant. I can ping 192.168.1.20 and all is well. I can ping the
external IP and all is well. Then if I pull the cable on Server 1,
Server 2 picks up fine -- I can ping 192.168.1.20 and all is well.
However the external IP does not forward to 192.168.1.20. It acts as
if the forward is non-existent for Server 2. If I plug Server 1 back
in and unplug Server 2 so Server 1 takes back over, the external IP
forwards again.

I'm thinking this has something to do with UCARP's multicast. There is
traffic to a multicasted IP of 224.0.0.18. Is it possible this router
(Kentrox q2300) is having trouble with this multicasted IP address?

I guess I'm just looking for ways to troubleshoot where the problem
with this is. What gets me is that the LAN IP works great in all
regards, it's just the forwarding of the external IP address is
problematic. How can I get UCARP to use a broadcasted address rather
than multicasted one so I can try that?

Thanks guys,
Chris