[Pacemaker] Wrong system send arp reply when using IPaddr

Andrew Beekhof andrew at beekhof.net
Sun Mar 17 21:01:22 EDT 2013

On Mon, Mar 18, 2013 at 3:17 AM, David Coulson <david at davidcoulson.net> wrote:
> First off, I'm going to preface this with the realization that what I am
> explaining makes no sense, doesn't follow normal logic and I'm not a
> complete idiot. I've beaten my head against a wall with this issue for two
> days, and have made no progress, yet we've had a couple of production system
> outages because of it.
> Environment is a pair of IBM x-series systems in a DMZ connected to an
> ASA5500. Each IBM box has two interfaces in a mode=4 bond connected to two
> switches, which connected to the pri/sec firewall and are interconnected -
> Poor man's redundancy I support. Both boxes run RHEL6.3 and Pacemaker
> 1.1.7-6.el6-148fccfd5985c5590cc601123c6c16e966b85d14. ASA has a ARP table
> timeout of 4hours.
> There are about a dozen IPAddr resources in a group which are configured
> with meta ordered="false" collocated="false" - Each is independent from a
> service perspective, but the group makes it easy to manage them. Each box
> runs LVS with mangle rules, then assigns fwm values for routing within LVS -
> For whatever reason, this still requires the IP to be on the box receiving
> the packet through LVS, even if the mangle rule is triggered.
> We've had a couple of instances for two IPs in this configuration where
> Pacemaker (and syslog) indicate the IP is assigned to box 01, yet the
> firewall receives an ARP reply from box 02. Didn't believe it at first until
> we grabbed packets from a SPAN on the switches. Correct IP address in reply,
> MAC of one of the bonded interfaces on box 02, yet the IP isn't on it.
> We've experienced both 01 arping for an IP on 02, and 02 arping for an IP on
> 01. Last night when we had the issue, an IP was on 02, 01 arped for it and I
> tcpdumped on 01 and saw SYN packets coming in for the IP on 01 - Makes
> sense, but doesn't explain why the box answered the arp in the first place.

Had pacemaker just failed over the IP?
Did you set any ARP related options for the resource?

> I realize this likely isn't a Pacemaker issue, but I was hoping someone else
> might have experienced a similar issue, or can at least point me in the
> right direction. We have a far more complex Pacemaker/LVS environment on our
> inside network (which isn't link-local to the ASA - goes through an inside
> router) which works flawlessly, so I'm open to the fact that something is
> totally screwed up in our DMZ.
> Sorry that was long. :)
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