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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: "James Yonan" <jim@xxxxxxxxx>
  • Date: Sat, 6 Mar 2004 10:31:31 -0000

Evan Harris <eharris@xxxxxxxxxxxxx> said:

> 
> > 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.

Basically OpenVPN supports --local which binds to a single interface.  Without
--local, it will bind to all interfaces.  There's not really any middle ground
right now.

Binding to multiple IPs and using multiple sockets is a more involved change,
though the infrastructure to do it will be in 2.0 which is under development
right now.

James