[LARTC] routing for split multiple uplinks/providers with port forwarding

From: "Ian! D. Allen" <idallen@idallen.ca>
To: lartc@vger.kernel.org
Subject: [LARTC] routing for split multiple uplinks/providers with port forwarding
Date: Sat, 01 Nov 2003 15:50:31 +0000	[thread overview]
Message-ID: <marc-lartc-106770352107516@msgid-missing> (raw)

The fine document:

  http://lartc.org/howto/lartc.rpdb.multiple-links.html

works nicely to make sure that answers to packets incoming to the
Linux router from a particular provider go back out again over the
same provider.

It doesn't work as given for connections that are port forwarded from the
Linux router to machines inside the local network (e.g. to a web server).

With port forwarding in the mix, packets arriving from the Internet to a
particular port on the Linux router have DNAT applied so that they pass
transparently on to the internal web server; but, the answer packets from
the web server arrive back at the Linux router and do not necessarily
go out by the same gateway/provider by which they came in.

I suspect the fix is somehow to mark the port forwarded packets with
a flag indicating on which interface they arrived at the Linux router,
and then preserve this flag into the answer packets on the web server.
On the Linux router I can then make sure that appropriately flagged
answer packets go out the correct interface.

Am I on the right track here?

-- 
-IAN!  Ian! D. Allen   Ottawa, Ontario, Canada
       EMail: idallen@idallen.ca   WWW: http://www.idallen.com/
       College professor via: http://teaching.idallen.com/
       Board Member, TeleCommunities CANADA  http://www.tc.ca/
_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/