Re: ARP problems with xen 4.0 with pvops kernel

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 06/01/2010 05:38 PM, Luís Silva wrote:
> Hello,
>
> Finally I managed to get a xen 4.0 working on ubuntu 10.04 with pvops
> kernel and libvirt. However I am having some problems with
> networking... after initial installation with netinstall image in hvm
> mode, when I transform the vm in xen pv (via pygrub with the current
> ubuntu kernel), networking startEd to act weird...
>
> Basically I'm not using a network script from xen. I define a bridge
> (manually or via libvirt, the result is the same) and I use vif-bridge
> to connect the vif to it. But now the weird part comes: I can
> communicate from domU to dom0, but not the other way around, unless I
> keep a ping running from domU to dom0... That's right, weird... while
> trying the ping from dom0 to domU, I used tcpdump both on the bridge,
> on the vif and on the eth0 in the domU. The arp packets never get to
> domU, but they appear both in the bridge and the vif sniff's...

What version of kernel are you using in dom0 and domU?  There was a
netback bug which caused problems with dom0<->domU communication, but it
has been fixed for a while in 2.6.32 (but only recently in .31).  The
workaround is to disable tx checksum offload on your bridge (ethtool -K
<bridge> tx off).

    J

>
> Here is the bridge:
> ifconfig virbr0
> virbr0    Link encap:Ethernet  HWaddr fe:ff:ff:ff:ff:ff  
>           inet addr:192.168.120.254  Bcast:192.168.120.255  Mask:255.255.255.0
>           inet6 addr: fe80::7cee:4bff:fe82:e63f/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:16 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:226 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0 
>           RX bytes:952 (952.0 B)  TX bytes:13953 (13.9 KB)
>
>
> brctl show
> bridge name	bridge id		STP enabled	interfaces
> virbr0		8000.feffffffffff	no		vif5.0
>
>
> tcpdump -i virbr0 -vv -n
> tcpdump: listening on virbr0, link-type EN10MB (Ethernet), capture size 96 bytes
> 01:31:25.945151 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 1, length 64
> 01:31:26.945361 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 2, length 64
> 01:31:27.945420 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 3, length 64
> 01:31:28.945362 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 4, length 64
> 01:31:29.945364 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 5, length 64
> 01:31:30.944300 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:30.945359 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 6, length 64
> 01:31:31.944297 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:31.945444 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 7, length 64
> 01:31:32.944294 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:32.945401 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
>     192.168.120.254 > 192.168.120.1: ICMP echo request, id 10317, seq 8, length 64
> 01:31:33.947293 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:34.947373 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:35.947353 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:37.948352 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:38.948399 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:39.948376 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:31:40.949356 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
>
>
> tcpdump -i vif5.0 -vv -n
> tcpdump: WARNING: vif5.0: no IPv4 address assigned
> tcpdump: listening on vif5.0, link-type EN10MB (Ethernet), capture size 96 bytes
> 01:32:19.956358 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:20.956358 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:21.956359 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:23.957311 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:24.957312 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:25.957359 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:27.958360 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:28.958310 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
> 01:32:29.958362 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.120.1 tell 192.168.120.254, length 28
>   
>
>
> Forwarding and iptables don't seem to be the problem, because if I
> initiate a ping from domU (at the same time as the failing one from
> dom0), the ping in dom0 starts to work. As soon as I stop the ping in
> domU, the one in dom0 starts failing again...
>
> Is anyone having the same problem? Is this a bug in the kernel? In
> dom0 or domU?
>
> Thanks in advance,
> Luís
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>