Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.os.linux.networking > #2986

Re: Establish an alternative connection to an embedded system

Show all headers | View raw

perf60@gmail.com wrote:
> kl. 10:09:21 UTC+2 søndag 22. juni 2014 skrev Andrzej Adam Filip følgende:
>> perf60@gmail.com wrote:
>>
>>> I have an embedded linux system on a remote farm. Usually I ssh into
>>> the system via the farms ADSL/WiFi system (using port forwarding). But
>>> sometimes the traffic on the farm blocks me from connecting.
>>
>>> To solve this, I have added a GSM/GPRS modem to the system. The modem
>>> uses the gsmmux giving 3 channels /dev/mux0 thru /dev/mux2. I have a
>>> python daemon watching SMS messages om /dev/mux1. Then I can send an
>>> SMS telling this daemon to set up ppp on /dev/mux0. After the link is
>>> set up, the daemon answer the SMS telling me the IP number of the
>>> alternative link.
>>
>>> Problem is, it does not work to ssh into this IP. Something is obviously missing in my setup - it only works from the system towards the internet.
>>> What must I do to enable ssh to access my system via this alternative connection?
>>
>> 1) Have you changed ListenAddress in /etc/ssh/sshd_config ?
>> 2) Have you implemented source based TCP/IP routing to make _both_ links work
>>    at the same time? [unless your system is for monitoring only]
>> 3) Have you used tcptracerourote to track TCP connections attempts?
>>    [ There may be a firewall in between ]
>> 4) AFAIR some GSM internet providers block incoming TCP connections.
>>    You may try to overcome it by making outgoing ssh connection over GSM link
>>    with -R port forwarding
> 
> Thanks for your answer!
> 
> 1) No, ListenAddress is commented. The default is to listen on all local addresses - so do I need to spesify?

No. Default is listening on all interfaces.

> 2) No, I do not have the knowledge yet. I believe this is a problem. I guess I will have to write scripts in the /etc/ppp/ip-up.d and ip-down.p that should modify routing. My system is only monitoring local devices. Any help is very welcome ;-)

It definitely can be the problem. If in your route table ('route -n')
are two routes to 0.0.0.0/0 and metric for ppp0 default route is higher
you have found it. :)

4) Andrew is right, "-R" option in SSH client. I'm still sleeping.

Back to comp.os.linux.networking | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 00:34 -0700
  Re: Establish an alternative connection to an embedded system Andrzej Adam Filip <anfi@onet.eu> - 2014-06-22 10:09 +0200
    Re: Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 01:46 -0700
      Re: Establish an alternative connection to an embedded system ein <ein@no.spam> - 2014-06-22 11:28 +0200
      Re: Establish an alternative connection to an embedded system ein <ein@no.spam> - 2014-06-22 11:36 +0200
        Re: Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 03:20 -0700
          Re: Establish an alternative connection to an embedded system Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2014-06-22 12:37 +0200
            Re: Establish an alternative connection to an embedded system ein <ein@no.spam> - 2014-06-22 13:45 +0200
              Re: Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 05:15 -0700
                Re: Establish an alternative connection to an embedded system Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2014-06-22 14:20 +0200
                Re: Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 05:46 -0700
                Re: Establish an alternative connection to an embedded system Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2014-06-22 15:05 +0200
                Re: Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 06:26 -0700
                Re: Establish an alternative connection to an embedded system Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2014-06-22 15:47 +0200
                Re: Establish an alternative connection to an embedded system perf60@gmail.com - 2014-06-22 07:02 -0700
  Re: Establish an alternative connection to an embedded system David Brown <david.brown@hesbynett.no> - 2014-06-22 14:45 +0200

csiph-web