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Re: [Openvpn-users] Problem with openvpn on multi-homed host


  • Subject: Re: [Openvpn-users] Problem with openvpn on multi-homed host
  • From: Evan Harris <eharris@xxxxxxxxxxxxx>
  • Date: Sat, 6 Mar 2004 02:10:50 -0600 (CST)

> Okay, so you basically want a mode where OpenVPN ignores the source address on
> received UDP datagrams and doesn't use them to determine the address to send
> the next packet

Unfortunately, that's not the problem.

I need OpenVPN to pay attention to the destination ip of a recieved udp
tunnel packet, and use that as the source address of the outgoing tunnel
communication, even if it goes out of a different interface on the
multihomed host OpenVPN server.

I did a bit more research, and it looks like a semi-solution might be to use
the --local option to force a bind just to the public ip.  I'm assuming that
the replies will then come from the ip of the public interface in that case.
(I'll have to test it to check, but it seems logical).  Think that would
work?

Unfortunately, that's still only a partial solution, because I can see cases
where there might be more than one outside interface, and both would need to
be able to serve up vpn traffic, and would still need to pick the right
source ip to reply with based on the dest ip of incoming packets.

If using the --local option does in fact work, then a "whole" solution might
be to add a parameter for openvpn allowing for multiple ip's to be bound at
the same time (for multiple interfaces) rather than to IN_ADDR_ANY when more
than one interface needs to be enabled for traffic.  This would also give
more flexibility in configuration, in that you may not want to bind to all
ifaces, but need more than one.

I wonder how it works with ip aliases (different ip's on the same
physical interface)...  I might have to play with that and see.

Evan