dynamic IP without Dynamic DNS

jesnow · l33t Joined: 26 Apr 2006 Posts: 856

Why? Because.

Machine A has a static IP address and is on a fast net connection.

Machine B has a dynamic IP address, behind multiple levels of NAT.

I want to log into machine B from machine A WITHOUT using a dynamic dns server, but how would I do this? Seems to me machine B could ping machine A in some way on a regular basis to let A know its ip address. After all, I can ssh from B to A no problem, it's the *reverse* direction that's hard. I could start a demon on A that listens on a particular high numbered port for a connection, the client demon on B connects to that port, and drops its identity and IP address, maybe with some authentication. The demon on A then logs the ip to /etc/hosts (or updates the bind configuration and restarts if anything's changed) and we're off. Hackers might use this procedure to log in the bots they have infected, so there must be some code out there. As it happens I do control this bot, it's mine.

WHY don't I want to use dynamic dns? Because. So "just use dynamic dns" is not the answer I'm looking for, I know how to do that.

I know this forum loves a challenge.

javeree · Guru Joined: 29 Jan 2006 Posts: 453

If it is multiple levels of NAT, even dynamic DNS would present a challenge.
Maybe you would be ok with using zeroconf to broadcast B's presence by name and miniupnp to pass through the NAT levels. I think you should adapt the iptables rules that miniupnp installs for each NAT level.

jesnow · l33t Joined: 26 Apr 2006 Posts: 856

Maybe not multiple levels. It was when my DSL modem gave out one local private ip address, then my wireless router gave another, but now they're combined. Anyway, DDNS worked sorta, but had other issues.

ChrisJumper · Advocate Joined: 12 Mar 2005 Posts: 2390 Location: Germany

Its all easy.

If you have a Machine in the Internet with a fix IP adress. You could build a VPN or SSH forwarding Tunnel from your dynamic Machine. That Way you could set up a "fix" IP Adress to that other Machine.

I did not setup this myself but i am sure that you could buy or lease a Ipv6 Address Range That you should route from the Static IP Adress to your Dynamic IP Machine.

But be aware that the connection itself, your Dynamic Client have to update and reinitialize the Tunnel. Its nice to work with, but a strange setup to find bottlenecks.