Subject: Re: DF bit copying in gif processing
To: Jun-ichiro itojun Hagino <>
From: Jason R Thorpe <>
List: tech-net
Date: 09/14/2000 09:23:12
On Fri, Sep 15, 2000 at 01:12:25AM +0900, Jun-ichiro itojun Hagino wrote:

 > 	jason, where is the reason for your change to gif code, namely
 > 	sys/netinet/in_gif.c, "copy DF bit from inner to outer"?
 > 	(revision 1.14 -> 1.15)
 > 	i think we should make it configurable.  if we are to automate the
 > 	configuration, we must check net.inet.ip.mtudisc at least.
 > 	a meta problem here is that there are too many tunnelling specification
 > 	there, and they all state different things (this is not the place
 > 	to discuss, but anyway...)  see comment in sys/netinet/ip_encap.c
 > 	for (probably) full list of tunnelling RFCs which uses ip proto #4/#41.

I looked at each of those RFCs... It's been a while since I made the change,
so I may be remembering incorrectly, but I'm almost certain that each of
them said that if the DF bit is present on the inner packet, it must be
present on the outer packet as well.

If I read it wrong, well... let's fix it, I guess.  The previous behavior
wasn't exactly optimal, either :-)

        -- Jason R. Thorpe <>