From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: In-Reply-To: Your message of "Mon, 19 May 2014 23:49:22 +0930." <537A12EA.4060604@davidnewall.com> From: Valdis.Kletnieks@vt.edu References: <537621AC.1060409@davidnewall.com> <5379FFFD.1050705@davidnewall.com> <20140519140119.GA24523@breakpoint.cc> <537A12EA.4060604@davidnewall.com> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1400561749_1944P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Tue, 20 May 2014 00:55:49 -0400 Message-ID: <14456.1400561749@turing-police.cc.vt.edu> Subject: Re: [Bridge] Revert 462fb2af9788a82a534f8184abfde31574e1cfa0 (bridge : Sanitize skb before it enters the IP stack) List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Newall Cc: Stephen Hemminger , Netdev , bridge@lists.linux-foundation.org, Florian Westphal , Linux Kernel Mailing List --==_Exmh_1400561749_1944P Content-Type: text/plain; charset=us-ascii On Mon, 19 May 2014 23:49:22 +0930, David Newall said: > How does a packet get fragmented in this case? Does it only happen when > bridging to a device with smaller MTU? That scenario sounds quite > un-bridge-like. It also sounds like something that can be handled by > real routing. Which doesn't change the fact that you *will* get clowns who take a box that has a 10G card on a jumbogram-enabled subnet that's running with an MTU of 9000, and a 1G at MTU 1500 on the other, and try to bridge rather than route. (Did you know that you can actually mount an NFS filesystem across that? And that ls and cat and friends will work *just fine*? Until you hit a file that's more than 1.5 in size, that is. And when you do a traceroute to the wedged client, it tells you it's on the 10G network, so you have no idea why you're seeing an MTU issue. Don't ask how I know this - let's just say that supporting HPC users is never boring. :) So yes, we *do* need to do something sensible there - either frag the packet on the way out, or something. It *would* be nice if we could drop the packet and send an ICMP Frag Needed back - except it's unclear what IP you use as the source address for the ICMP.... --==_Exmh_1400561749_1944P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Exmh version 2.5 07/13/2001 iQIVAwUBU3rgVQdmEQWDXROgAQKQfw/9GcqjwTRblsTMBAzRms+9859yNW++iOKG N4cYN4Y1eip5ygc7ijvkiUOtTBq4UwwG+9rNkj0UwD1ZWCWiA9glN/n5bGvPY8qX brWW9QJAitZwN3yVJDc7+S6KyP62j+0q0f0xlFlfDNvEwNJ17d2v9ZG8PpzTJpfk bqxIIuTJzLY5UUjXM5RXGkDiw62eqb4e7aGL+nKOH52C/r8byEjY0yl2AmiqCAQD aFM8kLAITz/f2UB/KaTtu3i9b1Kv0Um/sRTHxULqN1jYHW1MqnenuAYw+ushoBTZ jRjpN2KdUDW7xGYz5Lx8bVnMxU8kJs5kmMVjnjbRsYmDA5v1jcoac+mGDLiQ8O6K 6VuJIrZ8e5pnJWFa2kcg1Syi2ca+Mi+pFRJGboMZQYw9KTQzx5lfQtgFdsyme40N 0A+MUc6eVeSCXITjmwhCmYanxLeEpOw4xlwYANoBWRXlUGCj4knB6zW5s6JwLrsu 9eGhag+t3mCYbM1cRN/Jru2Y7IB7bApnnKZsUdWkg0RoJJLX2WHF/26/u2Edi9He FawVStF76ZWtWNtZElrdFy1FPvg+jBjVPuzZs+tjyH5LW11Qlmt757ISSn/vnbCX sL4LNv8SXioBZenMMH4+sYh9Wh/LvyIn7egggzdvAzzYDU7Tm+niWnFJm2HLGETi svyoYnJozT4= =KX4i -----END PGP SIGNATURE----- --==_Exmh_1400561749_1944P--