Proper Port Forwarding

Michael Powell nightrecon at
Thu Jun 7 17:15:02 UTC 2012

Michael Sierchio wrote:

> On Wed, Jun 6, 2012 at 11:31 AM, Simon <simon at> wrote:
>> This easily causes DoS for when too many FIN_WAIT_2 are created and IPFW
>> stops forwarding using the rule above because of "too many dynamic rules"
> Change the defaults for the fw.dyn sysctl MIB nodes
> to something like
> net.inet.ip.fw.dyn_short_lifetime=3
> net.inet.ip.fw.dyn_udp_lifetime=3
> net.inet.ip.fw.dyn_rst_lifetime=1
> net.inet.ip.fw.dyn_fin_lifetime=1
> net.inet.ip.fw.dyn_syn_lifetime=10

There is also this you can place in /etc/sysctl.conf:


I do this for my web servers. It helps reduce the volume somewhat  of 
FIN_WAIT_2 from building up by expiring them sooner. 


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