[LARTC] Setting an alias as the "default" IP address,

[Carl Brewer <carl@vivitec.com.au>]

Hello,
Ive had a poke around through various linux routing documents,
but haven't found what I think is an elegant solution to a
routing issue I'm having with a hosting provider and RHEL ES 4 running
in a VMware VM.

Here's a diagram of the situation :


      Default route
      at provider         our host (A)
      72.3.230.1/26 ---- 72.3.230.30/26         the VM (B)
                         192.168.239.1/24 ----- 192.168.239.2/24
                                                72.3.205.160/32


I need to have the 72.3.205.160 address be used by the
linux box B in the VM as its default IP address - ie :
when traffic goes out from it (originating) it needs
to go out the 72.3.205.160/32 interface and then
via the 192.168.239.2 to .1 (default route).

This setup is because the hosting vendor will only allocate
us /32 addresses in addition to the base IP address they supply, which
is fine if we run them as aliases on eth0 on our host, but doesn't work
so well in a VM (you can't attach a route to a /32 that I'm
aware of, if you can, I'd *love* to know how!)

Does anyone here have a suggestion for the neatest way to
do this?  At present I have the 192.168 network and a static
route on A pointing the 72.3 address via 192.168.239.2 as that
seemed to be the easiest way to do it, and inbound traffic
works fine, but I haven't found a way to make the box in the
VM use the 72.3.205.160 address as its source when it originates
traffic, so things like DNS queries etc don't work unless I
also NAT outgoing traffic on A, which I'd prefer not to do unless
there's no alternative.  Maybe a bridge between the two?  I don't
really have a handle on the VMware bridge setup (it's VMware
workstation 5.0 at the moment). so maybe it's something that
would be better done in VMware, but I'd prefer to use a purely IP
routing solution if possible so we're not tied to VMware (at some
point I want to migrate this to xen or seperate hardware).

Should I maybe use a tunnel?  I have no experience with tunneling, and
not really sure of how it would solve the problem


Any suggestions?

Thanks!

Carl




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