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Re: [Xen-users] Binding Xen vm migration traffic to travel over 1 network card (nic)

Benjamin Weaver wrote:

Is the binding to a particular nic achieved through Xend configuration? or is it done externally, by adding routes, etc.?

OK, first off it's not a Xen issue, rather a general IP routing issue - the key is understanding how kernel routing works.

There are several ways to achieve what you are looking for.

The first, and probably simplest is to have a separate network for management traffic. Add a second NIC in each physical machine, and hook them all together either via a switch, or for two machines, with a cable. Use a private network address on the management network, and address management traffic to the private addresses. Eg, if you give hsot1 the IP address, and the second, then you could simply route management traffic via that network by using the appropriate address.

Ie, if on host1 you send traffic to, then the kernel will automatically route it via the management network since it's a directly connected network.

As I said, this is by far the simplest and needs no manual intervention to routing tables. It works because by default, the kernel will always route traffic for "locally connected" hosts via a directly connected network - ie if a host is in the same subnet, then it can be reached without going through any routers. Only if the destination isn't directly connected will it start looking for other routes - most usually a single default router.

If you want to still refer to hosts by their "frontend" addresses/URLs, then you could setup the same backend/management network, but you'd need to put explicit routing rules in. It's outside my area of expertise, but I would have thought you should be able to put in a static host route (on host1) so that a.b.c.d routes via, and the corresponding reverse route on host2 of a.b.c.e routes via I'm not sure if you need to do anything special to make this route take priority over the directly connected route via the frontend network.

There are probably some more "imaginative" and complicated techniques, but I suspect the first will do you.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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