[CentOS] conntrack-tools and Session syncing

Dirk H. Schulz dirk.schulz at kinzesberg.de
Wed Aug 13 08:27:13 UTC 2008

Hello Nataraj,

--On 12. August 2008 22:56:48 -0700 Nataraj <incoming-centos at rjl.com> wrote:

> On Sun, 2008-08-10 at 20:28 +0200, Dirk H. Schulz wrote:

- snip -

>> The setup works - using "conntrackd -e" I can see the connection table
>> entries the other router's conntrackd has synchronized. What I cannot
>> check  is if the receiving conntrackd writes the received entries into
>> the kernels  connection tracking table.

- snip -

> Also: cat /proc/net/nf_conntrack

Okay, that was good (it is ip_conntrack, but never mind). Now I now that 
the kernel connection table does NOT get updated. Just have to find out 

> The doc says you must have kernel 2.6.18 or later. It looks like there
> are some iptables features that you can use that will not allow this to
> work. Are you in compliance with all of the dependencies listed in
> http://conntrack-tools.netfilter.org/conntrackd.html ?

Yes, the libraries are installed. The kernel should meet the prerequisites:
CONFIG_NF_CONNTRACK_IPV4=m: no, did not find it, could not enable it

So only CONFIG_NF_CONNTRACK_IPV4 module is missing, but I thought that 
connection tracking would not work at all (even on just one netfilter 
instance) if a dedicated module für IPv4 additionally to the general 
NF_CONNTRACK module would really be needed.

Is there a debug mode for conntrackd where I can get more verbose logging 
to find out why conntrackd does not update the kernel connection table? 
Docs do not mention a debug mode, but maybe ...

By the way, when committing manually (conntrackd -c) I get the following 
entries in the log:
> [Tue Aug 12 12:51:49 2008] (pid=22668) [notice] Committed 139 new entries
> [Tue Aug 12 12:51:49 2008] (pid=22668) [notice] 2 entries can't be 
> [Tue Aug 12 12:51:54 2008] (pid=22671) [notice] committing external cache
> [Tue Aug 12 12:51:54 2008] (pid=22671) [ERROR] commit: Invalid argument
> Tue Aug 12 12:51:54 2008	tcp      6 180 SYN_SENT src= 
dst= sport=54930 dport=22 [UNREPLIED] src= 
dst= sport=22 dport=54930
> [Tue Aug 12 12:51:54 2008] (pid=22671) [ERROR] commit: Invalid argument
> Tue Aug 12 12:51:54 2008	tcp      6 180 SYN_SENT src= 
dst= sport=54929 dport=22 [UNREPLIED] src= 
dst= sport=22 dport=54929
> [Tue Aug 12 12:51:54 2008] (pid=22671) [notice] Committed 139 new entries 
[Tue Aug 12 12:51:54 2008] (pid=22671) [notice] 2 entries can't be committed

Why can not all cache entries be committed? I did not find much about this. 
My kernel is a 2.6.18-92.1.6.el5 (CentOS 5).

Thanks for your help.


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