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
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