Re: [Xen-users] Strange Networking Issue

[Jonathon Jones <xen@xxxxxxxxxx>]

Well, I did as you suggested and changed the netmask for x.x.153.178 to 255.255.252.0 and rebooted the machine just to give a clean slate.  I'm still in the same situation though.  Xen just isn't forwarding the packets to the domU for some reason.  I can watch the ping requests come in but since the IP is not bound to dom0, it doesn't respond to the request and the domU isn't responding to it, nor is it receiving the request according to tcpdump.

I just don't understand why xen isn't forwarding the traffic for some IP's but it is for others.  The only commonality to the IP's that do work are that they are the primary IP bound to eth0 in the domU.  It seems to me that if that IP works then any other IP's should work, especially if added tot he interface with the same network mask and everything so that ip addr show lists them the same way....

*confused and frustrated*

Jon

jez wrote:

On Sat, Mar 10, 2007 at 04:33:03PM -0500, Jonathon Jones wrote:
  

jez wrote:
    

It sounds like at the moment they are treating each of your 8 addresses
as host addresses (probably in a /22 block). Question: If you add each
of theses 8 addresses to eth1 on Dom0 like:

   ip addr add xxx.xxx.154.240/22 dev eth1

can you ping each address?

If you can, then you should be able to use a bridging setup on Dom0 and
keep all 8 addresses.

 
      

No, using the command you gave me does not allow the IP addresses to 
work.  However, adding them individually does like:
       ip addr add xxx.xxx.154.247 dev eth1
    

I meant you to add them individually. I think you might be confusing
what the /22 means. It doesn't mean "add this block of addresses" - it
means "add this address with a netmask of 255.255.252.0". If you do an
"ip addr show" at the moment you will see that each of your new
addresses have a /32 mask which means 255.255.255.255. 

Anyway, it's  good news for you that all your addresses are presently
considered host addresses. Before trying anything else, remove all those
addresses we just added to eth1 - execpt the .178 one of course.

What I recommend that you try is to configure eth1 on Dom0 with a /22
netmask instead of the /29 that it has now. It should appear as
x.x.153.178/22 to "ip addr show". Why? well, at the moment eth1 isn't on
the same subnet as x.x.x.240 - 248. If eth1 wanted to send a message to
one of those addresses it would send it to the router at x.x.153.177. 
Whereas, if you change it's mask then it will try to contact those 
addresses directly.

After that, configure each of the DomUs with all their addresses having 
a /22 mask also. Keep using the same default gateway (x.x.153.177) for all 
machines. 

If things aren't working, sniff the lines with tcpdump to get an idea 
of what's happening.

Let us know how you get on.


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