[ILUG] Heartbeat and intelligent switches

[Paul Jakma]

On Mon, 6 Jun 2005, Niall O Broin wrote:

> I've used heartbeat (http://www.linux-ha.org) a few times before, 
> rather successfully - it just works. However, I'm now looking at 
> deploying it fro a project in a large organisation which has a very 
> expensive network infrastructure and there is some concern about 
> how their switches will react when packets from IP address w.x.y.z 
> suddenly start arriving in on port B when they used arrive on port 
> A (I presume this is an ARP issue of some sort). This has never 
> been an issue whenever I've used heartbeat before, but it has been 
> raised by the networking people in this organisation.

It shouldn't be a problem at all as far as common switches are 
concerned. They only look at the MAC addresses and MAC<->port 
relationshop, which won't change by using heartbeat.

For anymore fancy switches which feel the need to inspect IP headers, 
heartbeat does gratuitous ARP on takeover, iirc - which should update 
any MAC<->IP state in snoopers. That said switches which inspect IP 
headers typically do so for optimising multicast, and they do it by 
monitoring IGMP messages - so this would be out of scope for 
heartbeat. (And not a concern unless your application uses 
multicast). Finally, for switches which do so, it tends to be 
configurable (IM*VL*E) via some kind of 'igmp snooping' option.

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
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