From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: PROBLEM: Fragmentation issue with 1521 bytes ip packets Date: Tue, 15 May 2012 17:04:19 +0200 Message-ID: <1337094259.8512.1100.camel@edumazet-glaptop> References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Omar Alhassane Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:63497 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752928Ab2EOPEY (ORCPT ); Tue, 15 May 2012 11:04:24 -0400 Received: by bkcji2 with SMTP id ji2so4897751bkc.19 for ; Tue, 15 May 2012 08:04:23 -0700 (PDT) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2012-05-15 at 10:00 -0400, Omar Alhassane wrote: > Hello Folks, > > I think i may have found a problem with the linux networking stack. > Below is a description of the problem. > > [1.] One line summary of the problem: > No response to pings of certain sizes. > > [2.] Full description of the problem/report: > Using hping3, when i ping a linux machine with 1521 bytes ip packets i > get only one response. > But when i use 1482 bytes, everything works fine. I've tried this with > both tcp and udp. The MTU of my interface is 1500. > [3.] Keywords (i.e., modules, networking, kernel): > ip, udp, tcp, networking, fragmentation > [4.] Kernel version (from /proc/version): > 3.3.1 > [5.] Output of Oops.. message (if applicable) with symbolic information > [6.] A small shell script or example program which triggers the > problem (if possible) > The following commands works only if the target has tcp port 22 open > > hping3 -d 1481 -S -P 22 10.0.30.225 (only one response) > hping3 -d 1482 -S -P 22 10.0.30.225 (works fine) > > Can somebody confirm if this is a problem? hping3 bug : All the fragments it sends have the same ID field. First 2 frags are reassembled by remote. Remote sends a SYNACK. Following frags are 'ignored' because they have same ID than previous packet.