Re: [Xen-devel] ARP problems in -testing?

["Ron Watkins" <xen-devel@xxxxxxxxx>]

I. Am. An. Idiot.

Thanks, Derrick.

<<RON>>

----- Original Message ----- 
From: "Derrik Pates" <demon@xxxxxxxxxxxxx>
To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Cc: "Jan Kundrát" <jan.kundrat@xxxxxx>; "Ron Watkins" <xen-devel@xxxxxxxxx>; 
<xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Sent: Sunday, January 16, 2005 7:27 PM
Subject: Re: [Xen-devel] ARP problems in -testing?


> Keir Fraser wrote:
> > The MAC addresses from the tcpdump log look sane. The problem must lie
> > elsewhere.
> I just tried this on a dedicated server located at thePlanet in Texas; I 
> think this is an issue that combines the following:
>   - No MAC address specified causes a random MAC address to be selected at 
> domain create time
>   - The upstream router has a local ARP cache
>   - The host system's ARP cache for addresses on the virtual NIC for the 
> instance is blown out when the virtual interface disappears when the 
> domain is destroyed
> This seems to explain why tcpdump shows packets going to the VM's IP, but 
> TCP sessions and ICMP packets don't get a response - the switch still 
> knows the "old" MAC address, but the first outbound packet to the outside 
> world implicitly eradicates the old ARP-cache entry. I don't think this is 
> Xen's fault at all, just a property of the implementation of ARP 
> resolution. I just happened to notice that the MAC shown in incoming 
> packets didn't match the current MAC address (based on ifconfig's output), 
> so this is my current theory on what's happening.
> --
> Derrik Pates
> demon@xxxxxxxxxxxxx
>
>
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