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Re: [Xen-users] Networking how does it really work?

If you want help, you'd do well to make it easy for people to read your messages.

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

1 Don't top-post.
2 Trim unnecessary quoted material - usually follows from top-posting and being completely oblivious to all the old material down off the bottom of the message.

3 In your case, you've also posted formatted text that comes out (on my system) as **tiny** pale blue text which is incredibly hard to read. I very nearly didn't bother at all.

Rafael Weingartner wrote:

I found out the problem with my VMs and the network.

Take a look at the annexed picture(is it possible to look it?).

I have that structure over virtual box instances.
So, each instance has a interface that connects it to the others VMs in the virtual box network.
My NFS server

There is nothing on the diagram labelled NFS Server

has 2 network interfaces, one that is plugged with the virtual internal network created by virtual box and another which has access to the internet using NAT provided by virtual box.

This network created by virtual box, does not have a gateway or router. It is like a simple hub where I can plug the PCs. The PCs in that network can see each other because they are in the same network level( without a router/gateway.

So When my VMs over the Xen server( get the IP address on the virtual box DHCP, they get the IP address at the same network level( That is why the VMs over the Xen server can see each other. And they are directly "plugged" to the Xen server, that is why they also can access the Xen server.

But my VMs over the virtual box instances do not have a route to the VMs that are over the Xen server instances. As an example, when my VM-2 tries to ping the gateway(, the ping goes to the server, passing by the bridge in the Xen server. But when the server( answers, it does not know how to access the VM-2. That server cannot find a route to VM-2. They are at the same network level but they need a gateway to "keep in touch".

Rubbish. If the network is as you describe, and the Xen server is indeed running in bridged mode, then no routes are needed for any device on that diagram to talk to any other device - they are all local to each other. That is basic networking.

But since your diagram doesn't match your text description (there is nothing labelled "virtualbox" either), it's a bit hard to say any more.

Draw yourself a diagram (pencil and paper will do) showing the **network** - that includes switches/hubs/etc. Don't forget that a bridge in your Xen host is also a switch as far as the network packets are concerned.

Also, looking at earlier messages, it's clear your network is incorrectly set up. Your DHCP allocated the same IP to a client as is used by the gateway - that's pretty fundamental and needs fixing. I don't know how Xen networking scripts deal with DHCP clients, but I do know that they support basic filtering of traffic based on the configured IP address. If Xen is picking up the clients IP address as configured via DHCP (though I don't see how it would) then when you statically assign a different address the filtering would be wrong.

Just as a check, what does "iptables -n -L" on your Xen host say (with the guests running) ?

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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