I have a script maintaining gre tunnels and firewall rules using the "ip" and "iptables" tools. Setting up hundreds of tunnels, and adresses per interface runs just fine. Takes less than 0.1 second per interface, however when I get around to do the firewall rules everything slows down spending >0.5 per insertion.

Why is it running so slow? What can I do to improve the speed?

It seems like I could try ipset instead, but I really feel there is something wrong with the kernel or something. The interesting thing is that the first 10 rules runs fast, then it slows down..

mybox(root) foo# iptables -V
iptables v1.3.5
mybox(root) foo# uname -a 
Linux foo 2.6.18-164.el5 #1 SMP Tue Aug 18 15:51:48 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
mybox(root) foo# cat test.sh
#!/bin/sh

for n in {1..100}
do
  /sbin/iptables -A OUTPUT -s ${n} -j ACCEPT
  /sbin/iptables -D OUTPUT -s ${n} -j ACCEPT
done
mybox(root) foo# time ./test.sh

real    1m38.839s
user    0m0.100s
sys     1m38.724s

Appriciate any help. Cheers!