Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261280AbUJ2Dbx (ORCPT ); Thu, 28 Oct 2004 23:31:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262248AbUJ2Dbx (ORCPT ); Thu, 28 Oct 2004 23:31:53 -0400 Received: from mail1.webmaster.com ([216.152.64.168]:40975 "EHLO mail1.webmaster.com") by vger.kernel.org with ESMTP id S261280AbUJ2Dbv (ORCPT ); Thu, 28 Oct 2004 23:31:51 -0400 From: "David Schwartz" To: , Subject: RE: ICMP ttl-exceeded packets not sourced correctly Date: Thu, 28 Oct 2004 20:31:44 -0700 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.6604 (9.0.2911.0) Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 In-Reply-To: <20041029010721.GA25817@core.citynetwireless.net> X-Authenticated-Sender: joelkatz@webmaster.com X-Spam-Processed: mail1.webmaster.com, Thu, 28 Oct 2004 20:08:18 -0700 (not processed: message from trusted or authenticated source) X-MDRemoteIP: 206.171.168.138 X-Return-Path: davids@webmaster.com X-MDaemon-Deliver-To: linux-kernel@vger.kernel.org Reply-To: davids@webmaster.com X-MDAV-Processed: mail1.webmaster.com, Thu, 28 Oct 2004 20:08:22 -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1222 Lines: 32 > Say you have a router, and it's multihomed to two different isp's, > say cogentco.com and qwest.net as your upstreams. > On your cogent interface, you have the ip address on the /30 > assigned by cogent, > with reverse dns being blahblah.demarc.cogentco.com on the qwest > interface. > Same story with qwest, with reverse dns being whatever.qwest.net. > Now let's say someone out on the internet with ip address of 1.1.1.1 runs > a traceroute into your network and his incoming path to your > network comes over qwest. > Your router's hop should source its ICMP ttl-exceeded code (the > traceroute hop) on > its qwest /30 ip address, because thats where the traceroute got > triggered. > ICMP ttl-exceeded code's response should not be originated from > the interface > holding the route, but should be origianted from the interface > that got hit > with the traceroute. Why? If the same machine has two IP addresses, reaching one is the same as reaching the other. DS - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/