[LARTC] Configuring a redundant ethernet connection

[Doug Kingston <douglas.kingston@db.com>]

I am interested in setting up a host with dual ethernet connections to the same 
IP subnet (but different switches) for redundancy.  We need reasonably 
transparent failover if an interface fails.  In studying the existing HOWTO 
documents and other stuff produced by Google, it looks like the configuration in 
section 4.2 of the HOWTO (Routing for multiple uplinks/providers) comes close to 
setting up what we need, but there are some issues:
1. As implemented, traffic is segrated by destination and transparent failover 
is not possible.  If an interface fails, connections would need to be 
re-established.
2. Traffic is sourced with an interface specific address.
3. Incoming traffic would be bound to one or the other and at best would need to 
rely on something like DNS round robin at connection setup time - not ideal.

Though I have not tried this yet, it looks like one might be able to setup a 
dummy interface with a third IP address on the same subnet, and then proxy arp 
for that address from either of the real interfaces.  This virtual address is 
the one you would advertise via DNS as the machine's "primary" address, and this 
address would be used as the Source address on all outgoing packets.

Has anyone attempted to set up a redundant interface in this manner or something 
similar?  How would I arrange for the proxy arping that would be necessary to 
get traffic for the virtual interface delivered to the real one?  Is there a 
better way?

If I get this working - I will write up the HOWTO...

-Doug-

-- 

Douglas Kingston
Director
Global Unix Engineering Manager

Deutsche Bank AG London
6 Bishopsgate
London EC2N 4DA

Work:	+44-20-7545-3907
Mobile:	+44-7767-616-028

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