Networking issue with "conntracking" after upgrade Xen 3.2 > 4.0

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Networking issue with "conntracking" after upgrade Xen 3.2 > 4.0

Olivier Hanesse
Hi,

I recently upgraded a debian xen 3.2 system to xen 4.
Then I started to see some strange kernel logs : "nf_conntrack: table full, dropping packet."

I was pretty sure not to have enable conntracking in my dom0.
I find out that it was the revision "19540" of the "vif-common.sh" script that load the nf_conntrack module.

So now my dom0 logs every connection my domU are doing. With a few domUs, I am reaching the limit of conntrack table very quickly.
On debian the default "net.netfilter.nf_conntrack_max" is set to "16400".
I set it to "65536" to temporary resolve my network issue but that's not the point.

Is it possible to add an option in the xend-config.sxp configuration files, something like (handle_iptable yes/no), if we want to handle iptable or not ?

Moreover, for example on on debian, FORWARD policy is set to ACCEPT by default. So adding theses rules are useless BUT they are loading some modules which can lead to a network issue :(

Regards

Olivier

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Re: Networking issue with "conntracking" after upgrade Xen 3.2 > 4.0

Fajar A. Nugraha-4
On Fri, Dec 17, 2010 at 10:48 PM, Olivier Hanesse
<[hidden email]> wrote:
> Hi,
>
> I recently upgraded a debian xen 3.2 system to xen 4.
> Then I started to see some strange kernel logs : "nf_conntrack: table full,
> dropping packet."

Are you using bridged networking? If yes, see
http://lists.xensource.com/archives/html/xen-users/2009-08/msg00614.html

--
Fajar

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Re: Networking issue with "conntracking" after upgrade Xen 3.2 > 4.0

Keir Fraser-4
In reply to this post by Olivier Hanesse
iptables stuff has been there a while, even in Xen 3.2. The difference is a
new rule that requires conntrack to be loaded and used. I think the best
thing is to remove that requirement and be more permissive about what can be
sent to the domU. After all the domU can run its own firewall if it cares.

I have fixed this as xen-unstable:22573 and xen-4.0-testing:21415.

 Thanks,
 Keir

On 17/12/2010 15:48, "Olivier Hanesse" <[hidden email]> wrote:

> Hi,
>
> I recently upgraded a debian xen 3.2 system to xen 4.
> Then I started to see some strange kernel logs : "nf_conntrack: table full,
> dropping packet."
>
> I was pretty sure not to have enable conntracking in my dom0.
> I find out that it was the revision "19540" of the "vif-common.sh" script that
> load the nf_conntrack module.
>
> So now my dom0 logs every connection my domU are doing. With a few domUs, I am
> reaching the limit of conntrack table very quickly.
> On debian the default "net.netfilter.nf_conntrack_max" is set to "16400".
> I set it to "65536" to temporary resolve my network issue but that's not the
> point.
>
> Is it possible to add an option in the xend-config.sxp configuration files,
> something like (handle_iptable yes/no), if we want to handle iptable or not ?
>
> Moreover, for example on on debian, FORWARD policy is set to ACCEPT by
> default. So adding theses rules are useless BUT they are loading some modules
> which can lead to a network issue :(
>
> Regards
>
> Olivier
>
>
> _______________________________________________
> Xen-devel mailing list
> [hidden email]
> http://lists.xensource.com/xen-devel



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Re: Networking issue with "conntracking" after upgrade Xen 3.2 > 4.0

Olivier Hanesse
Thanks Keir.

Fajar : I think this option just disables iptables rules on bridged traffic (prerouting,forward and postrouting chain)
But as soon as the conntrack module is loaded, it starts to "track" network traffic. And this module is loaded as soon as you add 'stated' rules on iptables.


2010/12/17 Keir Fraser <[hidden email]>
iptables stuff has been there a while, even in Xen 3.2. The difference is a
new rule that requires conntrack to be loaded and used. I think the best
thing is to remove that requirement and be more permissive about what can be
sent to the domU. After all the domU can run its own firewall if it cares.

I have fixed this as xen-unstable:22573 and xen-4.0-testing:21415.

 Thanks,
 Keir

On 17/12/2010 15:48, "Olivier Hanesse" <[hidden email]> wrote:

> Hi,
>
> I recently upgraded a debian xen 3.2 system to xen 4.
> Then I started to see some strange kernel logs : "nf_conntrack: table full,
> dropping packet."
>
> I was pretty sure not to have enable conntracking in my dom0.
> I find out that it was the revision "19540" of the "vif-common.sh" script that
> load the nf_conntrack module.
>
> So now my dom0 logs every connection my domU are doing. With a few domUs, I am
> reaching the limit of conntrack table very quickly.
> On debian the default "net.netfilter.nf_conntrack_max" is set to "16400".
> I set it to "65536" to temporary resolve my network issue but that's not the
> point.
>
> Is it possible to add an option in the xend-config.sxp configuration files,
> something like (handle_iptable yes/no), if we want to handle iptable or not ?
>
> Moreover, for example on on debian, FORWARD policy is set to ACCEPT by
> default. So adding theses rules are useless BUT they are loading some modules
> which can lead to a network issue :(
>
> Regards
>
> Olivier
>
>
> _______________________________________________
> Xen-devel mailing list
> [hidden email]
> http://lists.xensource.com/xen-devel




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Re: Networking issue with "conntracking" after upgrade Xen 3.2 > 4.0

Fajar A. Nugraha-4
On Fri, Dec 17, 2010 at 11:30 PM, Olivier Hanesse
<[hidden email]> wrote:
> Thanks Keir.
>
> Fajar : I think this option just disables iptables rules on bridged traffic
> (prerouting,forward and postrouting chain)
> But as soon as the conntrack module is loaded, it starts to "track" network
> traffic. And this module is loaded as soon as you add 'stated' rules on
> iptables.

True. But if you're using bridged setup, with the change it only
tracks dom0's traffic, not domU. Since you mentioned you see the
effect when you increase the number of domUs, this could be a quick
fix.

--
Fajar

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