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Re: [Xen-users] newbie in trouble with CentOS Xen


  • To: xen-users@xxxxxxxxxxxxx
  • From: Alexandre Kouznetsov <alk@xxxxxxxxxx>
  • Date: Thu, 04 Apr 2013 21:29:40 -0600
  • Delivery-date: Fri, 05 Apr 2013 03:31:09 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

Hello.

El 04/04/13 13:52, Dave Stevens escribió:
Please tell me, how many physical network cards does your server have?
How are they supposed to be used? Was any physical NIC added or
removed recently? Maybe some NIC just died? The change of NIC number
could confuse the network-script that badly. Did I told it was unstable?

well the MB is a Supermicro 2P with 2 nics on it, eth0 and 1. The
incoming line goes into a Cisco router and that sends packets to eth1 on
the MB. The nic hasn't changed recently, still using the usual one.
There is no add-in nic.

Great. Make sure, with "ifconfig -a" that eth0 is at least present (although inactive). If it's not in the output, it's probably dead and you will need an add-on card, and consider a soon change of the MB.


[root@skeena xen]# cat bulkley
name = "bulkley"
uuid = "27180e16-68fd-f419-d0d9-abebc2de4a98"
maxmem = 2048
memory = 2048
vcpus = 4
bootloader = "/usr/bin/pygrub"
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
vfb = [ "type=vnc,vncunused=1,keymap=en-us" ]
disk = [ "phy:/dev/VolGroup00/bulkley,xvda,w" ]
vif = [
 "mac=00:16:36:35:12:ee,bridge=xenbr0,script=vif-bridge",
 "mac=00:16:3e:52:61:ce,bridge=xenbr1,script=vif-bridge"
]
Please tell me, how is the network [supposed to be] configured within DomU? It has 2 network interfaces, are they both used and have IP address? Those IPs, are they public or private?


[root@skeena xen]# cat xend-config.sxp
[...]
# It is possible to use the network-bridge script in more complicated
# scenarios, such as having two outgoing interfaces, with two bridges, and
# two fake interfaces per guest domain.  To do things like this, write
# yourself a wrapper script, and call network-bridge from it, as
appropriate.
#
(network-script network-bridge-multi)

This one is the tricky one. You can look for
/etc/xen/scripts/network-bridge-multi
Surely it's the script that is making all the mess with eth and peth.


As the general solution to your problem, in case you just want to
"make it work back" and not doing any new implementation (Dom0 OS and
Xe upgrade would be probably cleaner if reinstalled), I would suggest
to re-do the networking configuration.

I'm agreeable, just not sure how

Set our bulkley DomU to not to startup automatically

Comment out "network-bridge-multi" line in xend-config.sxp.

I would remove the mention of "script=vif-bridge" in bulkley config file (just leave mac= and bridge=, let the defaults do the rest), but maybe it's unnecessary .

Reboot. Make sure you have got your eth1 and eth0 plain and clean ("ifconfig -a"), no peth or weired bridges.

Build two ethernet bridges, xenbr0 containing eth0 and xenbr1 containing eth1. Check CentOS documentation about that, not my strength.
I found this quick reference, maybe it will help:
http://wiki.xen.org/wiki/Network_Configuration_Examples_%28Xen_4.1%2B%29#Red_Hat-style_bridge_configuration_.28e.g._RHEL.2C_Fedora.2C_CentOS.29
http://www.centos.org/docs/5/html/Virtualization-en-US/ch-virt-bridge-errors.html

Make sure the correct bridges configuration is set up on boot automatically. I would leave the physical interfaces eth0 and eth1 without IP configuration, and set IP directly on the bridge (or at least it's the Debian used way, not sure if CentOS documentation suggests it differently). When I have a Xen machine with a DomU with public IP, my Dom0 does not have any IP address on the bridge that contains the public physical interface.

"brctl show" should display something like this:
xenbr0        8000.003048ce847e    no        eth0
xenbr1        8000.003048ce847f    no        eth1

And ifconfig should show eth0, eth1, xenbr0 and xenbr1. Not sure if virbr0 will be there, but should be problem in either case.


After this, your server will be ready to start the bulkley DomU with networking in bridged mode. Note that your DomU will need to have configured the right IP's on it's interfaces. I'm still not sure about NAT ghost in your setup.

Greetings.

--
Alexandre Kouznetsov

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