I was using it on my DD-WRT router. I need to increase incoming/outgoing TTL from 1 to 128. How to use this commands in OS X using (ipfw)?
iptables -t mangle -I PREROUTING -i `get_wanface` -j TTL --ttl-set 128
iptables -t mangle -I POSTROUTING -o `get_wanface` -j TTL --ttl-set 128
IPFW does not have any options to modify packet's TTL directly. It can match a packet that has particular TTL range, but does not have any rules to modify it. Here's complete ipfw syntax.
As you can see, action list is fairly limited: "ACTION: check-state | allow | count | deny | unreach{,6} CODE |\n" " skipto N | {divert|tee} PORT | forward ADDR |\n" " pipe N | queue N | nat N | setfib FIB | reass\n"
You could divert the packet to an application and let it modify and reinject it, but that would require a custom app to do it. Sort of what natd does, only instead of IP addresses and ports it would change TTL.
