Re: [Xen-users] Basic Network Bridge

[Eric Lindsey <eslindsey@xxxxxxxxx>]

Sorry Alexandre I never did get used to that reply-to-list instead of 
reply-to-author. Anyhow, here's what I've done:

Restarting dnsmasq and giving the network time was the first thing I tried. 
Neither helped. 

I built the bridge manually in the interfaces file, now my bridge is br0 (with 
the IP address), my physical Ethernet is eth0 and bridged (set to manual--no 
IP) and obviously eth1 still minding its own business in the WAN world. 

I've also implemented my NAT script again to make sure there aren't any other 
issues I'm missing. My LAN computers are now successfully getting DHCP from www 
(my server) again and are reaching the Internet. 

I've also hardcoded dnsmasq to listen on br0, instead of telling it everything 
except eth1. 

Now, when I boot the VM I can see once again in my dom0 logs, a DHCPREQUEST on 
br0, and a DHCPOFFER also on br0. But the VM never sees it. 

How can I use tcpdump to try and track down this problem? 

Thanks for your help,
Eric Lindsey

On Jun 21, 2012, at 9:23 PM, Alexandre Kouznetsov <alk@xxxxxxxxxx> wrote:

> Hi, Eric.
> 
> This really should go to the list, but maybe your screenshot is not welcome 
> there.
> 
> 1. Try to restart dnsmasq, maybe the network topology changes on Dom0 confuse 
> it (eth0 was a physical interface at first, now it's called peth0 and eth0 is 
> a bridge).
> 2. Your low level configuration config looks good. Check how is your IP 
> configuration: the bridge eth0 shall have the IP address assigned, not peth0.
> 3. Check, if the lack of response from DHCP server is persistent. The bridge 
> probably has set a "forward delay" (10 sec by default), so the communication 
> is not possible immediately after boot. Try to request DHCP configuration 
> manually some time after the boot. Try static IP configuration and ping.
> 4. Diagnose what's happening on your network with tcpdump, it should be able 
> to see all the traffic within the bridge.
> 
> Consider creating the bridges from interfaces file, to avoid re-naming and 
> keep the setup clear. Really, Xen's network-bridge script is a crap.
> 
> 
> El 21/06/12 18:56, Eric Lindsey escribiÃ:
>> Normally, dnsmasq is set to listen on all interfaces _except_ WAN. But I'm 
>> pulling my hair out trying to fix this so I removed even that restriction.
>> 
>> Sorry for the screenshot but I'm mobile at the moment.
>> 
>> On Jun 21, 2012, at 5:44 PM, Alexandre Kouznetsov<alk@xxxxxxxxxx>  wrote:
>> 
>>> Hello.
>>> 
>>> El 21/06/12 16:31, Eric Lindsey escribiÃ:
>>>> My /etc/network/interfaces:
>>>> ...
>>>> iface eth0 inet static
>>>> address 10.1.20.1
>>>> netmask 255.255.255.0
>>>> 
>>>> allow-hotplug eth1
>>>> iface eth1 inet static
>>>> address w.x.y.z
>>>> netmask 255.255.255.248
>>>> gateway w.x.y.z
>>> There is a general recommendation to create the bridge(s) manually (or 
>>> using your distribution standard means), not using -network-bridge script. 
>>> It give a much more predictable result.
>>> 
>>>> As you can see, eth0 is my LAN and eth1 is WAN. The box normally functions 
>>>> as a NAT router for everything on eth0 to connect to the Internet via 
>>>> eth1. However I have not installed those packages or changed my iptables 
>>>> to provide that functionality yet. This is still a bone stock installation 
>>>> of Debian and on dom0 I have Internet access and DNS is working.
>>>> 
>>>> dnsmasq has been configured to service DHCP requests and to listen on all 
>>>> available interfaces.
>>> Even on WAN interface? Hm.
>>> 
>>>> xen-create-image with appropriate parameters created me a DHCP virtual 
>>>> machine (also running wheezy and the 3.2.0 kernel) which starts 
>>>> successfully.
>>>> 
>>>> brctl show displays eth0 as a bridge connected to peth0 and vif4.0 (the ID 
>>>> of the PV VM). But the VM does not seem to have any kind of network access 
>>>> for some reason. The dom0 does not seem to be getting the DHCP requests 
>>>> from the VM. The VM never successfully obtains a DHCP lease. And even when 
>>>> I set static information in the VM, it is not able to ping the dom0. What 
>>>> am I doing wrong? I don't even know what information to post with this 
>>>> because I don't know where to try to start troubleshooting the problem. 
>>>> The key is, I don't want the VMs to have just Internet access (else I 
>>>> would bridge them to eth1). I want them to get full network access, 
>>>> including the ability to get DHCP from dom0.
>>> Can you please show the "vif=" line from your DomU config file, the output 
>>> of "xm list" and "brctl show"?
>>> 
>>> You also might want to check for netfilter configuration (iptables -L -v) 
>>> and the "forward delay" parameter of your bridges.
>>> 
>>> --
>>> Alexandre Kouznetsov
>>> 
>>> _______________________________________________
>>> Xen-users mailing list
>>> Xen-users@xxxxxxxxxxxxx
>>> http://lists.xen.org/xen-users
> 
> 
> -- 
> Alexandre Kouznetsov
> Systems Officer
> Ondore, S.A. de C.V.
> Tel. +52(55) 5559-0090
> E-mail alk@xxxxxxxxxx

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