[K12OSN] K12OSN a bit OT - how to make responses on the same interface request came in

["Terrell Prudé Jr."]

Julius Szelagiewicz wrote:
> Dear Folks,
> 	I am somewhat stumped with a simple networking scenario:
> eth0 - internal,
> eth1 - external fast, dhcp non-routable, default route,
> eth2 - external public address not very fast.
> 	I am using openvpn and for connections to other servers I can
> easily specify which interface to use. What I need to do is to connect to
> openvpn server process on eth2. Unfortunately packets come in on eth2 but
> travel out on eth1 - default. Source based routing is no help, since I am
> not just passing the packets based on the incoming interface, but I'm
> trying to push responses on eth2. Essentialy, on receipt on eth2 of an UDP
> packets on port 1194 I need to answer with UDP packet om port 1194 on
> eth2.
> 	The computers trying to connect have only private addresses from
> cable ISPs.
> 	Any suggestions? Please ...
> julius
>   

What I'd do is make a static route for this OpenVPN server, pointing to 
eth2's next hop.  Something like this:

  thedude at linuxbox# route add -host w.x.y.z gw a.b.c.d

where w.x.y.z is the OpenVPN box that you want to talk to, and a.b.c.d 
is eth2's next-hop router.  Now, if you have a bunch of OpenVPN boxes in 
the same subnet that you have to talk to--for example, the 44.55.66.0/24 
network, I'd do it like this:

  thedude at linuxbox# route add -net 44.55.66.0 netmask 255.255.255.0 gw 
a.b.c.d

where, again, a.b.c.d is eth2's next hop.

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