Re: [Xen-users] Bridging works fine under KVM but not Xen

["Glenn E. Bailey III" <replicant@xxxxxxxxxxxxxxxx>]

> I take it that you have confirmed (with "brctl show" and "ifconfig -a")
> that the vif and tap devices are being added to the bridge? Can you post
> the output of those two commands while things are running please.
>
> The other options are firewall rules and sysctl things to do with
> forwarding and arps etc. Posting the output of the iptables and sysctl
> commands might set of a light bulb for someone. Likewise the route
> command (in all cases I mean with whatever option shows all the current
> settings...)
>
> How are the guests getting their IP address? DHCP? Where is the DHCP
> server? If static then are you sure all the netmasks and subnets etc are
> correct?
>
> Have you checked the in-guest network settings, like gateway and name
> server? How do they compare to the working KVM guest? Have you also
> compared all of the host settings (brctl, ifconfig, iptables, sysctl,
> etc) in the two configurations?
>
> Are you using Xen4CentOS or some other Xen packages or perhaps building
> from source? Have you asked on any CentOS lists (they have a virt one I
> think) -- there may be folks there who are aware of some quirk.

Ok,

I think I've narrowed down the issue a bit. So, it appears that when I
do a the "xl create" it *does* create the tap interface and adds it to
the bridge. But, shortly after starting the DomU the interface
disappears. Example flow:

- Start DomU, vifX.0 and vifX.0-emu get created
- Both vifX.0 and vifX.0-emu get added to the bridge (xenbr0)
- Process list shows qemu-dm is looking for vifX.0-emu interface
"ifname=vifX.0-emu"
- Dmesg shows vifX.0-emu is down "xenbr0: port 3(vifX.0-emu) entered
disabled state"

Example:

After starting DomU:

[root@xen-dev ~]# ifconfig | grep vif
vif2.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
vif2.0-emu Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF

[root@xen-dev ~]# brctl show xenbr0
bridge name     bridge id               STP enabled     interfaces
xenbr0               8000.0025b50002fb       no                eth0

                vif2.0

                vif2.0-emu
Shortly after DomU starts to boot:

[root@xen-dev ~]# ifconfig | grep vif
vif2.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF

[root@xen-dev ~]# brctl show xenbr0
bridge name     bridge id               STP enabled     interfaces
xenbr0          8000.0025b50002fb       no              eth0

              vif2.0


I did an strace -f against the xl create to try and find out how it's
creating that tap interface, but it only shows it bringing it down and
then changing the mac. There were some udev rules in place called
"xen-backend.rules  xend.rules" but I removed them and still see the
same results.

As for the guests, I've tried dhcp and static addresses.

I'll also double check the CentOS list but I'm not 100% sure it's
specific to the distro. For giggles I installed SuSE (only other
distro supported on the hardware) and experienced the same behaviour.

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