From owner-freebsd-net@FreeBSD.ORG Mon Nov 11 15:03:13 2013 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 0BCB225B for ; Mon, 11 Nov 2013 15:03:13 +0000 (UTC) (envelope-from kpielorz_lst@tdx.co.uk) Received: from mail.tdx.com (mail.tdx.com [62.13.128.18]) by mx1.freebsd.org (Postfix) with ESMTP id C903C2D8B for ; Mon, 11 Nov 2013 15:03:12 +0000 (UTC) Received: from Mail-PC.tdx.co.uk (storm.tdx.co.uk [62.13.130.251]) (authenticated bits=0) by mail.tdx.com (8.14.3/8.14.3/) with ESMTP id rABExaAO024758 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Mon, 11 Nov 2013 14:59:36 GMT Date: Mon, 11 Nov 2013 14:59:37 +0000 From: Karl Pielorz To: freebsd-net@freebsd.org Subject: IP clash (arp: x is using my IP address y on em1!) - recovering? Message-ID: <5F431BB1ED5D1F3DB12CF1AD@Mail-PC.tdx.co.uk> X-Mailer: Mulberry/4.0.8 (Win32) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Nov 2013 15:03:13 -0000 Hi, I've got a couple of FreeBSD boxes (9.2-R). I just accidentally brought 'up' the same IP address on both. Sure enough the console logs a bunch of "arp x is using my IP address y on ..." style messages. I quickly took down the 'new' IP's on one box (in fact, I shut the whole box down). However the original box with the addresses stopped responding to traffic going to those addresses. I flushed the ARP table on another box - and tried pinging one of the IP's that clashed - and you get nothing back. You don't event get an ARP entry appearing for it - i.e. if both boxes are on the same LAN / IP address range. It'll quite happily respond to other IP's (on the same interface / MAC) - but not the one that got 'clobbered'. In the end I 'ifconfig' deleted the clashed IP's off the original box - and added them again to the same box. This seems to have resolved it. Is there some way of avoiding this in the future? - I guess it's some kind of 'defensive' move or something? - We've just never seen it in the past (the very occasional times we've brought up two IP's it's been on much older boxes). -Karl