iptables based rate limiting

iptables.txt

-A INPUT -i eth0 -p udp -m udp --dport 5060 -j SIP
#
-A SIP   -i eth0 -p udp -m udp --dport 5060 -m string   --string "INVITE" --algo bm --from 23 --to 28 -m comment --comment "Catch SIP INVITEs" -j SIPINVITE
-A SIP   -i eth0 -p udp -m udp --dport 5060 -m string   --string "REGISTER" --algo bm --from 23 --to 30 -m comment --comment "Catch SIP REGISTERs" -j SIPREGISTER
-A SIP   -m comment --comment "Catch and accept everything else" -j ACCEPT
#
-A SIPINVITE   -m hashlimit --hashlimit-upto 4/min --hashlimit-burst 4 --hashlimit-mode srcip,dstip,dstport --hashlimit-name anon-sip-rateinv --hashlimit-srcmask 24 -m comment --comment "Rate limit SIP invites" -j ACCEPT
-A SIPINVITE   -m limit --limit 10/min -j LOG --log-prefix "SIPINV DROP: "
-A SIPINVITE   -m comment --comment "Rate limit exceeded, reject" -j REJECT
#
-A SIPREGISTER -m hashlimit --hashlimit-upto 6/hour --hashlimit-burst 6 --hashlimit-mode srcip,dstip,dstport --hashlimit-name anon-sip-ratereg --hashlimit-srcmask 24 -m comment --comment "Rate limit SIP registers" -j ACCEPT
-A SIPREGISTER -m limit --limit 10/min -j LOG --log-prefix "SIPREG DROP: "
-A SIPREGISTER -m comment --comment "Rate limit exceeded, reject" -j REJECT