[ovirt-users] R: R: R: PXE boot of a VM on vdsm don't read DHCP offer

Fri Jul 3 10:32:41 UTC 2015

----- Original Message -----
> Hi Dan, guys
> 
> Sorry for very late follow-up, but we had a lot of other topics to fix just
> before to go back on this one.
> 
> We have tried another approach just to check if the kernel of the vdsm iso
> image used to install the host could create the problem I've reported to the
> list.
> 
> Now we have reinstalled the same hardware with latest CentOS 7.1, fully
> updated.
> Installed vdsm, then joined the oVirt cluster.
> 
> Well, we are observing the same behavior as before.
> No DHCP offer is reaching the booting VM, and:
> 
> brctl showmacs <bridge_if> show us the booting vm mac-address
> tcpdump -I <bridge_if> show us the dhcp offer coming from dhcp server.
> 
> We have also tried to remove ANY firewall rule.
> 
> It isn't a PXE issue (gPXE 0.9.7) but only a DHCP process issue. Infact, if
> we install a vm manually and assign a static IP, it works fine.
> If we switch to dhcp, the vm don't get the dynamic one.
> In this case, tcpdump on vm shows only the DHCP discovery, not the DHCP
> offer.
> 
> Any further suggestion/hint ?

I've observed this behavior in bug
https://bugzilla.redhat.com/show_bug.cgi?id=1230638
We also removed all firewall rules, checked iPXE and I also saw the requests
going out, but no replies getting to the VM.
But here it sounds like it isn't specific to bonds.
After all I did not find the solution yet.

It is probably a good idea to install the oS with a static IP, and then
switch to dhcp to then use tcpdump inside the vm to see what is reaching
the inside.

- fabian

> 
> RN
> 
> > -----Messaggio originale-----
> > Da: Dan Kenigsberg [mailto:danken at redhat.com]
> > Inviato: lunedì 18 maggio 2015 16:14
> > A: NUNIN Roberto
> > Cc: users at ovirt.org; ibarkan at redhat.com
> > Oggetto: Re: R: [ovirt-users] R: PXE boot of a VM on vdsm don't read DHCP
> > offer
> >
> > On Fri, May 08, 2015 at 03:11:25PM +0200, NUNIN Roberto wrote:
> > > Hi Dan
> > > Thanks for answering
> > >
> > >
> > >
> > > > Which kernel does the el7 host run? I think that Ido has seen a case
> > > > where `brctl showmacs` was not populated with the VM mac, despite a
> > > > packet coming out of it.
> > >
> > > Kernel is: 3.10.0-123.20.1.el7.x86_64, package is vdsm only. Brctl isn't
> > available within vdsm only package.
> >
> > Could you try upgrading to a more up-to-date
> > http://mirror.centos.org/centos-
> > 7/7.1.1503/updates/x86_64/Packages/kernel-3.10.0-
> > 229.4.2.el7.x86_64.rpm
> > ?
> >
> > bridge-utils is a vdsm dependency. It must exist on your host. Please
> > see if the mac of the vNIC shows up on `brctl showmacs` as it should.
> >
> > > >
> > > > Can you tcpdump and check whether the bridge propogated the DHCP
> > offer
> > > > to the tap device of the said VM? Does the packet generated by
> > > > `ether-wake MAC-of-VM` reach the tap device?
> > >
> > > Yes: host "see" the broadcast :
> > >         0.000000    0.0.0.0               255.255.255.255       DHCP
> > >         346    DHCP
> > Discover - Transaction ID 0x69267b67
> > > It came from the right MAC:
> > >         Source: Qumranet_15:81:03 (00:1a:4a:15:81:03)
> > > And it is tagged correctly:
> > >         802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 3500
> > >
> > > This is the offer, on the bond interface:
> > >         1.012355    10.155.124.2          10.155.124.246        DHCP
> > >         346    DHCP
> > Offer    - Transaction ID 0x69267b67
> > > Layer 2 info:
> > >         Ethernet II, Src: Cisco_56:83:c3 (84:78:ac:56:83:c3), Dst:
> > Qumranet_15:81:03 (00:1a:4a:15:81:03)
> > > Tagging on the bond:
> > >         802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 3500
> > >
> > > The tag is correctly removed when DHCP offer is forwarded over the
> > bond.3500.
> > > Here's the offer content, seems everything right:
> > >
> > >     Client IP address: 0.0.0.0 (0.0.0.0)
> > >     Your (client) IP address: 10.155.124.246 (10.155.124.246)
> > >     Next server IP address: 10.155.124.223 (10.155.124.223)
> > >     Relay agent IP address: 10.155.124.2 (10.155.124.2)
> > >     Client MAC address: Qumranet_15:81:03 (00:1a:4a:15:81:03)
> > >     Client hardware address padding: 00000000000000000000
> > >     Server host name: 10.155.124.223
> > >     Boot file name: pxelinux.0
> > >     Magic cookie: DHCP
> > >
> > > Nothing of this offer appear on the VM side.
> >
> > But does it show on the host's bridge? on the tap device?
> >
> > >
> > > ether-wake -i bond0.3500 00:1a:4a:15:81:03 (started from the host)
> > > reach the VM eth0 interface:
> > >         2.002028   HewlettP_4a:47:b0     Qumranet_15:81:03     WOL
> > >         116
> > MagicPacket for Qumranet_15:81:03 (00:1a:4a:15:81:03)
> > >
> > > Really strange behavior.
> > >
> > > Roberto
> 
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