9.7. Binding to Non-local Addresses

FIXME!! Don't forget to note that iproute2 NAT and binding to non-local IPs do not play well together. I disagree with this. Binding to a non-local socket, which was possible under kernel 2.2 with when the kernel was compiled with CONFIG_IP_TRANSPROXY, is available under kernel 2.4 via the /proc IP sysctl interface. If you wish to be able to bind to non-local sockets:

# echo 1 > /proc/sys/net/ipv4/ip_nonlocal_bind
Thanks go to Oskar Andreasson for his IP sysctl tutorial page. If using sysctl to allow binding to non-local IP doesn't solve your problem, then see if netfilter NAT can be used to solve this class of problem. Some people view the technique of binding to non-local IPs as spoofing, and indeed, it can be used for nefarious purposes, if an attacker controls a machine on the route between a target and a victim.