From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerd Knorr Subject: Re: RE: [patch, rfc] put IP addresses into xenstore (Gerd Knorr) Date: Fri, 23 Dec 2005 14:48:47 +0100 Message-ID: <43AC003F.50006@suse.de> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: "Bonnell, David" Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Bonnell, David wrote: > Arping sends ARP "who-has" requests, either broadcast or directed to a > specific MAC address and displays the responses. No. It does that if you ping an IP address, but not if you ping a MAC address. For pinging mac addresses it sends a ICMP ping, to the MAC address specified, with broadcast (IP-)address as destination in the header. And thats exactly the problem, machines tend to not respond to broadcast pings for security reasons (allows certain kinds of DoS attacks), so this isn't going to work reliable. Try "echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts" in your domU and receiving the IP address with arping doesn't work any more ... Another problem is that there are multiple arping versions out there, for example the iputils ship an arping utility to, and that one doesn't even support pinging hosts by MAC address. cheers, Gerd