iptables REDIRECT original destination-ip

hi

if i use ip_forward on a proxy and:
iptables -t nat -A PREROUTING -p tcp --dport 554 -j REDIRECT --to-port
9999
to catch RTSP-Packets and pass them to the 9999 port of the proxy, how
can i get the original destination-ip.

thx

Hello,

bubzilla a écrit :
>
> if i use ip_forward on a proxy and:
> iptables -t nat -A PREROUTING -p tcp --dport 554 -j REDIRECT --to-port
> 9999
> to catch RTSP-Packets and pass them to the 9999 port of the proxy, how
> can i get the original destination-ip.

Read the SO_ORIGINAL_DST option of the TCP socket.
Or look up the connection tracking table in /proc/net/ip_conntrack.

thankx

where is SO_ORIGINAL_DST defined , which header ???

bubzilla wrote:
> thankx
>
> where is SO_ORIGINAL_DST defined , which header ???

struct sockaddr_in addr;
bzero((char *) &addr, sizeof(addr));
addr.sin_family = AF_NET;
socklen_t addr_sr = sizeof(addr);

getsockopt(fd, SOL_IP, SO_ORIGINAL_DST, &addr, &addr_sz );

and of course:

#include <linux/netfilter_ipv4.h>