Get original destination IP and port with Linux 2.4 iptables redirect?

From: Lincoln Yeoh (junkto_at_tm.net.my)
Date: 11/12/03 

Date: Wed, 12 Nov 2003 20:12:29 +0800

Sorry to repost this but I still haven't figured it out and there
weren't any responses. 

---
Say I use iptables to redirect tcp connections to my perl proxy
servers. How then do I get the original destination IP address and tcp
port?
On FreeBSD I just use ipfw and fwd and then following works:
$daddr=$client->sockhost;
$dport=$client->sockport;
And then my various proxies work transparently.
But on Linux I'm supposed to use some FD options:
e.g.
  getsockopt(fd, SOL_IP, SO_ORIGINAL_DST, &dst_addr, &slen)
What's a good way to do this with perl? Working examples would be very
helpful.
I've tried perl's getsockopt but replacing OPTNAME with
SO_ORIGINAL_DST doesn't work - it's not defined.
perl -f getsockopt 
getsockopt SOCKET,LEVEL,OPTNAME
I've tried specifying a numerical 80 for OPTNAME but not sure how to
get the address etc.
Thanks,
Link.

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