From mboxrd@z Thu Jan 1 00:00:00 1970 From: thomas yang Subject: IP header identification field is zero, why? Date: Wed, 7 Oct 2009 22:04:34 +0800 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: QUOTED-PRINTABLE To: netdev@vger.kernel.org Return-path: Received: from mail-iw0-f178.google.com ([209.85.223.178]:35583 "EHLO mail-iw0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759058AbZJGOFL convert rfc822-to-8bit (ORCPT ); Wed, 7 Oct 2009 10:05:11 -0400 Received: by iwn8 with SMTP id 8so2835872iwn.33 for ; Wed, 07 Oct 2009 07:04:34 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: This is captured on my PC (Fedora 11, Linux=A3=A9 [root@localhost ~]# tcpdump -i eth1 icmp -n -x tcpdump: verbose output suppressed, use -v or -vv for full protocol dec= ode listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes 17:02:39.025882 IP 192.168.1.64 > 192.168.1.1: ICMP echo request, id 25096, seq 1, length 64 0x0000: 4500 0054 0000 4000 4001 b717 c0a8 0140 =2E..... 17:02:39.027866 IP 192.168.1.64 > 192.168.1.1: ICMP echo request, id 25096, seq 2, length 64 0x0000: 4500 0054 0000 4000 The IP header 'identification' field is zero, why? I wrote a simple UDP server and UDP client programs, and captured some packets, the IP identification is also zero. Should the host increase this field for each packet it sends? I captured some TCP packets, all of the IP identification are different, not zero. -- thomas