changing the ToS in IP Header

[Ashish Kulkarni]

Hello,


Is there any way in which I can manipulate the Type of Service (TOS) byte
in the IPv4 header? I need to set the TOS bits on all outgoing packets from
my box to the ISP to a particular pattern (0x02), as otherwise the ISP does
not forward packets. I have been able to do this in Linux using the
iptables mangle table:


http://www.tldp.org/LDP/nag2/x-087-2-firewall.tos.manipulation.html


but am unable to find a similiar packet-mangling feature in the firewalls
running on FreeBSD...there are rules for matching on TOS pattern, but not
on TOS manipulation. Does anyone know of any tool which can do this?


As an alternative solution, is there any way to set the default TOS via a
sysctl interface (similiar to that of TTL, namely  net.inet.ip.ttl)? I'm
planning to use this on my home box, so I have no problems in trying to
patch and rebuild the kernel if I can get some feedback and/or tips on how
to do so :-)


Thanks,
Ashish.


ps: can you please CC any replies to me? thanks...