C++ iptables redirection forming separate packets

Question

I have all traffic from port 50 redirected to 5050 using

iptables -t nat -A POSTROUTING -p udp --dport 50 -j REDIRECT --to-port 5050

I lis

Answer 1

Linux netfilter defines a socket option called SO_ORIGINAL_DST in .

First you need to enable port forwarding in your system, using one of these commands:

sysctl net.ipv4.ip_forward=1
echo 1 > /proc/sys/net/ipv4/ip_forward

Then you can use this:

struct sockaddr_in addr;
socklen_t addr_sz = sizeof(addr);
getsockopt(fd, IPPROTO_IP, SO_ORIGINAL_DST, &addr, &addr_sz);

I cannot find SO_ORIGINAL_DST in any Linux manpage. You may have luck finding formal documentation on the netfilter site.