Dynamic IP and pf?

Saad Kadhi saad at docisland.org
Fri Jan 14 12:09:06 PST 2005

On 14/01/2005 20:39 Christopher McGee wrote:
> I have a cable modem that provides a dynamic IP address to the outside 
> interface of my firewall(5.3 with PF doing NAT).  If my IP address 
> changes I have to run a script to update my dynamic dns and reload my 
> firewall rules based on the new IP address. Is there a recommended way 
> of doing this other than having cron check to see if the IP addresss has 
> changed?
the PF version integrated into 5.3 supports dynamic IPs by putting 
parentheses around the interface name as explained in 
http://www.openbsd.org/faq/pf/filter.html :
The name of a network interface in parentheses ( ). This tells PF to 
update the rule if the IP address(es) on the named interface change. 
This is useful on an interface that gets its IP address via DHCP or 
dial-up as the ruleset doesn't have to be reloaded each time the address 

for example :
nat on $my_if proto tcp from any to any -> ($my_if)
pass in quick on $my_if proto tcp from any to ($my_if) port domain flags 
S/SAFR keep state

Saad Kadhi
"He who relieves the poor makes Ahura king"

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