This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] arp during live migration

To: Jacob Gorm Hansen <jacobg@xxxxxxx>
Subject: Re: [Xen-devel] arp during live migration
From: Cristian Zamfir <zamf@xxxxxxxxxxxxx>
Date: Mon, 05 Mar 2007 15:40:18 +0000
Cc: "Graham, Simon" <Simon.Graham@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Mon, 05 Mar 2007 07:39:09 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <1172938895.14470.25.camel@xxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: 45E88EEA.4020707@xxxxxxxxxxxxx <342BAC0A5467384983B586A6B0B3767104DC3DAF@xxxxxxxxxxxxxxxxxxxxx> <1172938895.14470.25.camel@xxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Thunderbird (X11/20070104)

> In my case, I NEVER see the gratuitous ARP being sent (confirmed using
> tcpdump on peth0 in Dom0) and the return value from dev_queue_xmit is
> sometimes 0 and sometimes 2 (that's PLUS 2 -- congestion notification

I am seeing the same error, indeed it looks like it is NET_XMIT_CN. I also see 100% percent loss, the ARP never makes it to the wire in any of my tests.

If the ARP is only being used to advertise the move of the MAC to a new
port, it would be better to construct some kind of reliable protocol,
e.g. pinging a remote host (like the default GW) until an answer comes
back. This should be enough to make sure the switch got the message. If
the ARP is used for updating peer ARP caches, pinging everyone in the
guest's /proc/net/arp table until a majority have replied would be a

Given that I am seeing 100% loos, I am considering implementing something like this. However, I assumed that sending the arp broadcast in netfront works for most people using 3.0.3. Can anyone confirm that they are actually seeing the arp being sent on the wire with xen >= 3.0.3?


Xen-devel mailing list