From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mika Liljeberg Subject: Re: SCTP path mtu support needs some ip layer support. Date: 14 Jan 2003 08:46:04 +0200 Sender: netdev-bounce@oss.sgi.com Message-ID: <1042526764.2606.21.camel@devil> References: Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: kuznet@ms2.inr.ac.ru, Jon Grimm , davem@redhat.com, netdev@oss.sgi.com Return-path: To: Sridhar Samudrala In-Reply-To: Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org On Tue, 2003-01-14 at 02:56, Sridhar Samudrala wrote: > On 14 Jan 2003, Mika Liljeberg wrote: > > > Hi, > > > > I know this is not what the SCTP spec recommends with IPv4, but what > > prevents you from just fragmenting the IP packets at the source and > > setting the DF bit on each fragment (assuming you can't just repackage > > the data chunks)? This would be equivalent to the IPv6 behaviour and > > would keep PMTUD working perfectly. > > SCTP does segment the packets based on the current PMTU and sets DF bit to not > allowing IP fragmentation. The problem occurs when the PMTU shrinks and there > are outstanding segmented packets which need to be retransmitted. We cannot > re-segment these packets, but would like IP to fragment them by not setting > DF bit. Setting DF=0 allows intermediate routers to fragment the packets as well. I was proposing that you allow the IP layer to fragment the packets at source host only, and then set DF=1 on the IP fragments. This should keep PMTUD working nicely, since intermediate routers are not allowed to refragment. MikaL