[RndTbl] Bizarre netfilter behaviour

Sean Walberg sean at ertw.com
Wed Jan 11 15:54:47 CST 2012

Have you looked at /proc/net/nf_conntrack ?


On Wed, Jan 11, 2012 at 1:50 PM, John Lange <john at johnlange.ca> wrote:

> I'm hoping someone suggest a fix for this.
> We moved some applications over to a new server which still had the
> default firewall rules in place which included a rate limiting "drop"
> rule that looks like this:
> iptables -A input_ext -m limit --limit 3/min -m conntrack --ctstate
> NEW -j LOG --log-prefix "SFW2-INext-DROP-DEFLT " --log-tcp-options
> --log-ip-options
> In short, limit to 3 new connections per minute.
> It turns out this was way to short for our application and so I just
> removed all firewall rules by stopping the firewal (this is on
> OpenSUSE).
> The last firewall log message indicates that a packet was being
> dropped to a specific IP due to a rate limit but now the server will
> not send packets to that IP at all! tcpdump shows that the packets are
> not even attempting to leave the interface.
> It seems like netfilter blocked the ip on the rate limit rule and now
> its "stuck".
> I tried specifically allowing that IP and even recreated the limit
> rule thinking that would "reactivate" the chain but it doesn't work.
> My guess is that a reboot would fix it but the server is in production
> and can not be rebooted without a scheduled outage.
> The only other thing I can think of is to reload all of the netfilter
> kernel modules but again that is too risky on a production system.
> Any other ideas on how to clear the filter?
> Is there a command to display the current status of what netfilter is
> tracking and dropping?
> --
> John Lange
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> Roundtable at muug.mb.ca
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Sean Walberg <sean at ertw.com>    http://ertw.com/
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