On 11/07/2012 11:35 AM, William Murray wrote:
Dear list,
I have been trying to setup a PXE guess installation on Fedora
17 with no success.
I build a bridge, and connect my VM to it but DHCP times out in the VM
install.
I don't know how to debug this bridge. I guess I could connect a
'live' machine to it,
but what then?
I follow:
http://docs.fedoraproject.org/en-US/Fedora/13/html/Virtualization_Guide/sect-Virtualization-Network_Configuration-Bridged_networking_with_libvirt.html
and
https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/sect-Virtualization_Host_Configuration_and_Guest_Installation_Guide-Guest_Installation-Installing_guests_with_PXE.html
These guides almost work. Two differences show up:
brctl show
bridge name bridge id STP enabled interfaces
br0 8000.14feb5b90f56 no p5p1
virbr0 8000.525400da475b yes virbr0-nic
First make sure that ifcfg-br0 contains:
DELAY=0
as well as:
STP=on
which you have already shown is on.
When a new interface comes up on a switch or router, care needs to be
taken so that the interface does not cause Spanning Tree issues. Even
with fastboot enabled on switches and routers, there is a normal delay
for STP. That delay may be just long enough to prevent pxe from getting
a response. It is really an issue of a second or two.
Since the host is playing the role of the 'bridge', it is trying to play
nice on your network, which is correct. However, since the host
interface is already connected, a spanning tree issue is extremely
unlikely and it is normal and desirable to turn off the STP delay.
You can confirm this behavior using tshark on the bridge interface.
Your second question is whether the network sees the VM MAC or the host
MAC on that interface.
A network bridge device can have its own MAC and IP as well as pass
other packets 'raw' through its bridged interfaces. Those bridged
packets will not be wrapped and the VM client MAC(s) will appear in the
MAC table on the switch for that interface. They will work exactly as
if you had plugged the VM into the same switch as the host.
So your dhcp server for pxe needs to watch for the VM client interface
data, not the host.
Good Luck!
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