Conntrackd entries timing out

Conntrackd entries timing out

[Steve Hill]

I'm configuring conntrackd to support an active/active pair of 
firewalls.  I would like to keep them as synchronised as possible so am 
setting it up with FTFW mode and "DisableExternalCache On".

I'm monitoring the connection tracker records on both hosts with 
"conntrack -L".

If I send a single ping to something from firewall A, I correctly see 
the conntrack entry appear for that on both firewalls.  Since the I only 
sent 1 ping, I see the timer on both ticking down from 30 seconds, after 
which the entry disappears from both firewalls - this bit seems fine.

The problem I'm having is if I start a continuous ping from firewall A, 
sending 1 packet per second, I again see the conntrack entry appear on 
both firewalls as expected.  However, whilst firewall A shows the timer 
sat at 30 seconds since it is regularly being reset by each packet, 
firewall B's connection again ticks down and is then removed.  So now, 
the conntrack tables are unsynchronised - firewall A is still seeing the 
pings and keeps the conntrack entry alive whilst firewall B has removed 
the entry.

If I turn the external cache on and monitor it with "conntrackd -e", it 
appears to behave correctly - the entry stays in the external cache so 
long as it it in firewall A's conntrack table.

The only way I've found of keeping these machines correctly synchronised 
with the external cache disabled is to run "conntrackd -n" every few 
seconds on both hosts to force a resynchronisation, which does appear to 
reset the timers correctly.

So I'm hoping someone is able to answer these questions:
1. Is this a bug or is there something I'm missing about the way it is 
expected to work?
2. Is running "conntrackd -n" on both machines every few seconds a safe 
and feasible workaround, or am I asking for trouble?


Thanks.

-- 

  - Steve Hill
    Technical Director
    Opendium Limited     http://www.opendium.com

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Re: Conntrackd entries timing out

[Kerin Millar]

On 24/11/2011 17:29, Steve Hill wrote:
>
> I'm configuring conntrackd to support an active/active pair of
> firewalls. I would like to keep them as synchronised as possible so am
> setting it up with FTFW mode and "DisableExternalCache On".
>
> I'm monitoring the connection tracker records on both hosts with
> "conntrack -L".
>
> If I send a single ping to something from firewall A, I correctly see
> the conntrack entry appear for that on both firewalls. Since the I only
> sent 1 ping, I see the timer on both ticking down from 30 seconds, after
> which the entry disappears from both firewalls - this bit seems fine.
>
> The problem I'm having is if I start a continuous ping from firewall A,
> sending 1 packet per second, I again see the conntrack entry appear on
> both firewalls as expected. However, whilst firewall A shows the timer
> sat at 30 seconds since it is regularly being reset by each packet,
> firewall B's connection again ticks down and is then removed. So now,
> the conntrack tables are unsynchronised - firewall A is still seeing the
> pings and keeps the conntrack entry alive whilst firewall B has removed
> the entry.
>
> If I turn the external cache on and monitor it with "conntrackd -e", it
> appears to behave correctly - the entry stays in the external cache so
> long as it it in firewall A's conntrack table.
>
> The only way I've found of keeping these machines correctly synchronised
> with the external cache disabled is to run "conntrackd -n" every few
> seconds on both hosts to force a resynchronisation, which does appear to
> reset the timers correctly.
>
> So I'm hoping someone is able to answer these questions:
> 1. Is this a bug or is there something I'm missing about the way it is
> expected to work?
> 2. Is running "conntrackd -n" on both machines every few seconds a safe
> and feasible workaround, or am I asking for trouble?

You could use conntrack -E -p icmp to monitor the propagated events in 
both cases. That is, with and without the external cache active. In my 
case, I use the external cache and the lifecycle of the ICMP state is as 
thus:-

[NEW] src=x.x.x.x  dst=8.8.8.8 type=8 code=0 id=9243 [UNREPLIED]
       dst=196.34.134.87 type=0 code=0 id=9243

[UPDATE] src=x.x.x.x dst=8.8.8.8 type=8 code=0 id=9243
          src=8.8.8.8 dst=x.x.x.x type=0 code=0 id=9243

Eventually, after terminating ping ...

[DESTROY] src=x.x.x.x dst=8.8.8.8 type=8 code=0 id=9243 src=8.8.8.8
           dst=x.x.x.x type=0 code=0 id=9243

Observing the behaviour where the cache is not active might help shed 
some light on the situation.

Cheers,

--Kerin