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Re: [Xen-users] [Fwd: DHCP and DomUs troubles]


  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Arnaud JAYET <ajayet@xxxxxxx>
  • Date: Sat, 30 Jan 2010 17:56:12 +0100
  • Delivery-date: Sat, 30 Jan 2010 08:56:49 -0800
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Fajar A. Nugraha wrote :
On Sat, Jan 30, 2010 at 6:40 PM, Arnaud JAYET <ajayet@xxxxxxx> wrote:
2) i'm using Debian Lenny + Xen 3.2-1 for Dom0 and DomU

start with that.

The usual debugging method is to try deactivating checksum offload on
all interfaces (domU's ethx, dom0's vifx.y, dom0's ethx), try without
vlan, or change to newer kernel. But the thing is the default kernel
and Xen package on debian stable is simply old and unmaintained (I
assume you use the default package, last updated 24 Mar 2009?), and is
known to have some bugs, so sometimes it's a lot easier to simply jump
to using a newer Xen and kernel version.

Personally I use RHEL5 + default 2.6.18 kernel-xen + (on some servers)
updated Xen 3.4.x RPM from Gitco, works great. But changing distros
might be too much effort :D So what I suggest is you do is try see if
debian has newer xen kernel available (from unstable?) and use it for
dom0 and domU. If they don't have it, try using latest 2.6.31 kernel +
patch from http://code.google.com/p/gentoo-xen-kernel/downloads/list.


You're maybe right, Xen 3.2 is not the last version but i don't want to change my Debian Stable for RHEL, sorry ;-)

Well, i have solved the problem by disabling tx checksum Dom0's vifx.y of the domU.

let's say my domU has ID no. 39, after doing
'ethtool -k vif39.0 tx off' in dom0 it works ; when i launch dhclient on the domU, i get immediatly an IP address (tx is also disabled in domU by adding the line 'post-up ethtool -k eth0 tx off' in /etc/network/interfaces


I wonder now how i can automate disabling tx offload on vifx.y interfaces created when a domU is started ; manually by xm create command or at dom0 boot time with hard links in /etc/xen/auto to the config file ???


# xm list
Name       ID   Mem VCPUs      State   Time(s)
Domain-0    0   256     4     r-----     91.9
gwnat.dev   1   128     1     -b----     11.4
client.dev  3   256     1     r-----      1.4

# brctl show
bridge name     bridge id               STP enabled     interfaces
xenbr114                8000.0030482d925d       no              eth1.114
xenbr115                8000.0030482d925d       no              eth1.115
                                                        vif1.0
                                                        vif3.0

# ethtool -k xenbr115
Offload parameters for xenbr115:
Cannot get device rx csum settings: Operation not supported
Cannot get device flags: Operation not supported
rx-checksumming: off
==> tx-checksumming: off <===
scatter-gather: off
tcp segmentation offload: off
udp fragmentation offload: off
generic segmentation offload: off
large receive offload: off


DomU vif interfaces have tx-checksumming on by default :

# ethtool -k vif1.0
Offload parameters for vif1.0:
Cannot get device rx csum settings: Operation not supported
Cannot get device flags: Operation not supported
rx-checksumming: off
===> tx-checksumming: on <====
scatter-gather: on
tcp segmentation offload: on
udp fragmentation offload: off
generic segmentation offload: off
large receive offload: off

# ethtool -k vif3.0
Offload parameters for vif3.0:
Cannot get device rx csum settings: Operation not supported
Cannot get device flags: Operation not supported
rx-checksumming: off
===> tx-checksumming: on <====
scatter-gather: on
tcp segmentation offload: on
udp fragmentation offload: off
generic segmentation offload: off
large receive offload: off


------------

My dom0  /etc/network/interfaces file
eth0 = dom0 management (not used for xen bridges)
eth1 = vlans for domUs (here 2 tests VLAN 114 and 115) dot1q tagged

# Dom0 management interface
allow-hotplug eth0
iface eth0 inet static
        address 192.168.101.37
        netmask 255.255.255.0
        network 192.168.101.0
        broadcast 192.168.101.255
        gateway 192.168.101.254


### VLAN TEST 114
auto eth1.114
iface eth1.114 inet manual
auto xenbr114
iface xenbr114 inet manual
        netmask 255.255.255.0
        network 192.168.114.255
        bridge-ports eth1.114


### VLAN TEST 115
auto eth1.115
iface eth1.115 inet manual
auto xenbr115
iface xenbr115 inet manual
        netmask 255.255.255.0
        network 192.168.115.255
        bridge-ports eth1.115



--
Arnaud

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