Xen users - Oct 2011 - Dom0 IP Detection in Routed Mode

Hello Everyone,

my Xen server works with the networking in routed mode, with one exception
which I cant seem to resolve.

In Debian servers with Bridge Mode networking, when I bring a new IP up
inside a DomU using the command:
 ip addr add x.x.x.x/32 dev eth0
The IP is automatically detected by Dom0 and I can route to, connect to the
address immediately.

With the server I''m running in routed mode, when I bring up an IP
inside a
DomU with:
 ip addr add x.x.x.x/32 dev eth0 peer x.x.x.x/32 broadcast x.x.x.x
The IP comes up on the DomU, then I have to manually add routing for it on
the Dom0 with a command like:
 ip route add x.x.x.x dev vif8.0 scope link src x.x.x.x

I haven''t yet got to trying live migration, but I can already see how
this
is going to get inconvenient even with one server.

Is this a problem which has already been solved somewhere or is there
something in my setup I need to pay closer attention to in order to get this
running smoother? Ideally I would like to just define the IPs inside the
DomUs like I''ve always done with my routed mode VMs.

Thanks for your assistance,
-Aaron

Aaron Cossey
aaron.cossey@gmail.com


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Aaron Cossey wrote:
>With the server I''m running in routed mode, when I bring up an IP 
>inside a DomU with:
>  ip addr add x.x.x.x/32 dev eth0 peer x.x.x.x/32 broadcast x.x.x.x
>The IP comes up on the DomU, then I have to manually add routing for 
>it on the Dom0 with a command like:
>  ip route add x.x.x.x dev vif8.0 scope link src x.x.x.x
Yes, that is correct when you abuse IP addressing like that - and 
it''s nothing to do with Xen.

Normally, you would have both devices in the same subnet - and for a 
point to point link the smallest valid subnet is /30. So you''d have 
(eg) 192.168.1.13/30 on one end, and 192.168.1.14/30 on the other 
end, and each device will then automatically add a route of type 
"connected" for that subnet.


Doing /32 addressing like that, and adding specific routes, is one of 
those tricks used for working around other issues (such as lack of 
addresses).

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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