topic Re: IP forwarding in Operating System - Linux

IP forwarding

KRS_1 — Thu, 19 May 2005 14:22:25 GMT

Hi all,

Please let me know more about ip forwarding.

Any help will be appriciated with points

Thanks and Regards
Rajesh

Re: IP forwarding

Stuart Browne — Thu, 19 May 2005 18:06:09 GMT

IP Forwarding, as in routing, or as in address translation?

If for routing, then it's as simple as making sure that '/proc/sys/net/ipv4/ip_forward' contains a '1'. This is usually done via the 'sysctl' interface (which is configured via '/etc/sysctl.conf').

If you mean address translation, then I'll assume you're using a recent distribution and 'iptables'.

What you need to look at is the NAT table (Network Address Tralsnation) and the DNAT and SNAT jump types.

These rules live in the PREROUTING/OUTPUT and the POSTROUTING chains respectivly.

The key to adding these is the '--to' flag, i.e.

iptables -t nat -A PREROUTING -j DNAT -d 192.6.165.40 --to 192.6.165.119

This would force every request to 'www.hp.com' to one of the two IP's which respond to that name (NOTE: I use this only as an example, I do not suggest you try this!).

This can also modify the destination port, i.e.

iptables -t nat -A PREROUTING -j DNAT -p tcp --dport 80 d 192.6.165.40 --to 192.6.165.119:81

The SNAT rules work in the same manner.

These are discussed in the man page (man iptables) and also in great length in the IP Tables howto's, in particular the Netfilter Hack HOWTO, http://www.iptables.org/documentation/HOWTO//netfilter-hacking-HOWTO.txt .

Re: IP forwarding

Steven E. Protter — Thu, 19 May 2005 23:23:09 GMT

A frew firewall threads:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=871034

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=624078

SEP

Re: IP forwarding

Sergejs Svitnevs — Fri, 20 May 2005 07:16:52 GMT

ip forwarding means the system will route packets between interfaces.
Machine acts as a router: datagrams received on one interface are forwarded to another one.

Regards,
Sergejs

Re: IP forwarding

Chakravarthi — Fri, 20 May 2005 12:34:17 GMT

http://www.troubleshooters.com/linux/ip_fwd.htm

regards
chakri