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How can I connect to computer behind mobile phone?


firebrand
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I haven't got a landline at my house, so I connect my home computer to the internet via a cellphone or a mobile broadband dongle. I'd like to be able to connect to the machine when I'm out and about. I've got apache on the machine, so I got a DynDNS account and used my eeepc to see if I could view a test webpage I put on the home computer. It didn't work - all I got was a blank page.

I did some reading on the subject and learned that internet-connected phones and computers on a cellphone provider's network are behind a firewall that will only allow connections that are initiated from behind the firewall. Simply put, I can make a connection from my home computer out to another machine on the int.ernet, but I cannot make a connection from that other machine to my home computer.

I've been thinking about how I can get around this restriction. One idea I had was to send an email to my home computer with a special subject line that procmail would see and grab, and have some kind of commands in the body of the email that would tell the machine to connect to me. So the connection would be initiated by the computer behind the firewall. But I haven't really explored that idea because I don't know what I'm talking about.

I'm not really fussed about making my home computer available to other people. I want to be able to access it myself. I started thinking about all this after seeing that Hak5 segment about using DNS requests to get free internet access at cyber cafes whose systems allow DNS requests to go through. Hmm, that's worded pretty badly. I hope you know what I'm talking about?

Anyway, has anyone got any thoughts on how I might achieve this?

EDIT: I forgot to mention, my home computer is running Ubuntu Hardy, and my eee uses eeebuntu Jaunty. If that's at all important.

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I haven't got a landline at my house, so I connect my home computer to the internet via a cellphone or a mobile broadband dongle. I'd like to be able to connect to the machine when I'm out and about. I've got apache on the machine, so I got a DynDNS account and used my eeepc to see if I could view a test webpage I put on the home computer. It didn't work - all I got was a blank page.

I did some reading on the subject and learned that internet-connected phones and computers on a cellphone provider's network are behind a firewall that will only allow connections that are initiated from behind the firewall. Simply put, I can make a connection from my home computer out to another machine on the int.ernet, but I cannot make a connection from that other machine to my home computer.

I've been thinking about how I can get around this restriction. One idea I had was to send an email to my home computer with a special subject line that procmail would see and grab, and have some kind of commands in the body of the email that would tell the machine to connect to me. So the connection would be initiated by the computer behind the firewall. But I haven't really explored that idea because I don't know what I'm talking about.

I'm not really fussed about making my home computer available to other people. I want to be able to access it myself. I started thinking about all this after seeing that Hak5 segment about using DNS requests to get free internet access at cyber cafes whose systems allow DNS requests to go through. Hmm, that's worded pretty badly. I hope you know what I'm talking about?

Anyway, has anyone got any thoughts on how I might achieve this?

EDIT: I forgot to mention, my home computer is running Ubuntu Hardy, and my eee uses eeebuntu Jaunty. If that's at all important.

logmein.com or any other calling-out service like PCanywhere. There's lots of em. Those services make an outbound connection that you can ride back in, very simple.

My question is, are you going to leave your mobile dongle or cell phone on and attached all the time? I'm guessing your account will be promptly billed and disconnected at the end of that first day.

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logmein.com or any other calling-out service like PCanywhere. There's lots of em. Those services make an outbound connection that you can ride back in, very simple.

Cheers, I'll check that out.

My question is, are you going to leave your mobile dongle or cell phone on and attached all the time? I'm guessing your account will be promptly billed and disconnected at the end of that first day.

My cellphone plans are for "unlimited" data. I know what cellphone companies mean by "unlimited" is not what the rest of us understand by the term. But whatever their limits are, I haven't reached them yet. And I use phones and dongles a lot. I must download in excess of 6 GB of crap every month on each device I use (I watch a lot of video). As the cellular network is my only internet service at home, I cane it severely. But my provider doesn't seem to care. I have never been contacted by them concerning excess data use. I love 'em!

If anyone's interested, I pay £2.50 for 5 days' unlimited internet access. The surprising thing is, the plan is supposed to be for "mobile internet" on the phone only - it's against the terms of service to use it to connect a computer. But my current 3G phone is wonderful for linking the computer, and I use a sim card from a phone in the dongle so my provider thinks that's a phone too.

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Right, I had a look at logmein.com, and unfortunately it seems to be a Windows and Mac service only. Not for Linux (I'm running Ubuntu). Symantec's PCAnywhere is available in a Linux flavour, but it isn't free (I'm too poor to pay :( ) and anyway to use it you need to configure your firewall to let you in. I'm trying to defeat my cellular provider's firewall here.

I've been reading about Nokia's Mobile Web Server product. I thought maybe it would give me some insight into how I can make my computer reachable from the internet. Unfortunately, Nokia's solution involves custom gateways that allow connections to pre-specified urls. Which doesn't help me.

What deceptacon_eazy_e said about services that "make an outbound connection that you can ride back in" sounds like what I need. But I need one that'll work with Linux. I'm continuing to search, but if someone here can suggest a service or solution I'll be most grateful.

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Thanks for the tip. I'll check it out properly when I get home.

One question though: I just looked through that page you linked to, please tell me if I've got this right - do I have to establish an ssh connection between my home machine and my laptop before I go out, then maintain that connection all the time until I actually want to use it? Because that would be a problem. I want to be able to connect to my home computer when I am out and about with my laptop, maybe at a wifi hotspot at McDonald's or some such thing. So I wouldn't know the IP address my laptop would be using until I actually get to the hotspot or cyber-cafe.

Something I've been thinking: would it be feasible to email from laptop to home machine, sending my laptop's address? I could put a particular keyword in the subject line for procmail to watch for; then my home machine reads the email, gets the necessary info, and establishes a connection to my laptop? I can set Evolution to grab new emails every 10 minutes or something, so getting an email through to the computer won't be a problem.

This idea is definitely in the vague, "I don't really know how to implement this or even if it is actually implementable" stage. Is it something that I could actually do? Please remember, I'm trying to get round a firewall that does not allow connections from the outside to the home machine - it will only allow connections that are initiated from the home machine to the outside. I have absolutely no control over this firewall, so port-forwarding and anything else like that is not possible. I want to connect to a laptop (running Ubuntu) that I will have at a wifi hotspot. The home computer is also running Ubuntu. The eventual plan is to try and do the DNS-tunnelling demonstrated by mubix on Hak5 s5 e4.

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Thinking about it, I wouldn't have to set up the reverse ssh at home before I leave. If I can email my ip address at the hotspot to my home machine, I'll be able to have it automated, have a script set it up for me. Wouldn't I?

My ignorance is making it very difficult to see what is possible and what is just coming out of my butt. I'd love it if someone here with more knowledge of this stuff could give me some feedback on what I'm talking about. Please?

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To establish a connection you need one of either an open port one either end or an intermediary with an open port.

Without any one of these you would have to brute force a NAT traversal. Ignoring the practical issues has the problem of your attempt to connect looking like port scanning (whcih it quit literally is). Depending on your ISP this may render different results.

Brute force NAT traversal... interesting idea. You know the IP address of the client (some how) but neither you or the client have any open ports. So the server sends out a bunch of requests hoping the router on the other end is 'stealthed' so that the servers requests don't come back with a reset response. A client behind the router sends out a bunch of responses (hopeful the router doesn't block them realising that there is no way a request came in) on a range of ports the request probably came from hoping to hit a port that was open. There is the problem of communicating the IP address though. This is basically using an intermediary, but only using the intermediary to transmit the IP address and not an open port number. I doubt there is any existing implementation of this possibility however.

you should look in to services like GoToMyPC and Hamachie. Short of renting a server some where connecting two 'port closed' networks is really quite difficult. At whcih point, you may as well use hamachi or gotomypc.

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Use Hamachi. It's a private network VPN software thats free for a limited amount of computers. If you plan on running a corp VPN network then they'll want you to purchase a license.

Been happily using it for YEARS for my Windows & *nix boxes!

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