[plug] IP Alias/Arp dilemma...

[Trevor Phillips]

Here's a curly one:

I'm using IP Aliases to shift services from one host to another without needing
a DNS entry. ie; each Server has its primary unique name/IP, and then another
ip via an Alias for the service. Moving the service involves downing the Alias
interface on one, and upping it on the other.

At least, that's the theory.

The problem is, the router still has the ARP entry for the old alias, not the
new one, so no traffic from outside that subnet can find the new location. One
solution is to flush the arp cache on the router, but it's not in my power to
do that automatically (or to do it at all other than going through the COMMS
guys).

Any ideas on how to poke the Gateway to update the ARP entry? On Solaris it was
easy - outgoing traffic went out on a random/rolling interface, so traffic
going out on the new Alias would prod the gateway into revising its info.

However, Linux has all traffic going out the primary interface, which for most
things is a GOOD thing (eg; only have to add the one IP to your access list),
but it means it isn't getting that "poke" to get the gateway to update.

So, any ideas? Is there a way to force a Ping or something to go out a
particular aliased interface?

-- 
. Trevor Phillips             -           http://jurai.murdoch.edu.au/ . 
: CWIS Systems Administrator     -           T.Phillips at murdoch.edu.au : 
| IT Services                       -               Murdoch University | 
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