Subject: more notes on gre
To: None <>
From: David Young <>
List: tech-net
Date: 08/26/2006 13:53:44
On Sat, Aug 26, 2006 at 02:18:04AM -0500, David Young wrote:
> I need to tunnel packets through NAT routers to a tunnel concentrator at
> my office.  To that end, I am extending gre(4) to put tunnel packets into
> UDP datagrams.  I have attached a patch that contains my work in progress.
> I request your feedback.

This work may be a springboard for a Teredo developer, since Teredo
uses UDP to tunnel IPv6 packets through NAT firewalls.  I do not foresee
working on Teredo, myself.

While I was testing for regressions, I found that some bogus pointer
arithmetic has always kept gre's Mobile IP mode from working.  I fixed
that, but I could only test one gre(4) against another gre(4).  There's no
telling if it interoperates with anything.  Maybe the feature should
go away.

I noticed that gre(4) is missing both the capability to tunnel ethernet
packets, and the capability to tunnel through v6 networks.  The latter
should be easy to add.  The former will be more difficult.  Maybe this
will be somebody's project on a rainy day.


David Young             OJC Technologies      Urbana, IL * (217) 278-3933