WARNING - OLD ARCHIVES

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/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

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

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


-------------------------------------------------------
The SF.Net email is sponsored by: Beat the post-holiday blues
Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek.
It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel




-------------------------------------------------------
The SF.Net email is sponsored by: Beat the post-holiday blues
Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek.
It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel