From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: PMTU issues due to TOS field manipulation (for DSCP) Date: Wed, 10 Dec 2003 21:55:27 +0100 Sender: netdev-bounce@oss.sgi.com Message-ID: <20031210215527.239fb33f.ak@suse.de> References: <20031210203433.3747b7fd.ak@suse.de> <3FD7826F.1050308@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: ruddk@us.ibm.com, netdev@oss.sgi.com, chester.f.johnson@intel.com Return-path: To: Nivedita Singhvi In-Reply-To: <3FD7826F.1050308@us.ibm.com> Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org On Wed, 10 Dec 2003 12:30:39 -0800 Nivedita Singhvi wrote: > > I don't think the network users will be very happy if you require changing all > > end hosts this way. How about the following hack? For DF=1 packets > > the ipid field is useless. When you rewrite the TOS to DSCP save > > the old TOS in the ipid field. When you see an ICMP fragment required > > message with the right DSCP on the router restore the old TOS from the ipid > > field. > > Wouldnt this require changes at the both ends, router and > host? How would we sync? Only the router would need to change (and rewrite ICMP messages, which is a bit nasty, but then compatibility is not always fun) -Andi P.S.: I am not opposed to fixing linux for this, just I have my doubts that fixing all end hosts is a practical solution for the problem.