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Remote network debugging
Jan. 15th, 2018 01:55 pmMy parents recently had their DSL upgraded to FTTC. I had previously had an extensive conversation with Zen, the ISP, about the configuration of the supplied replacement DSL modem, to make sure it would just drop in and work. Sadly, the configuration described was nothing like the one shipped. The house server and firewall, which I manage, was expecting to have the house /29 delivered to it by the modem. The new modem, a "Fritzbox", seems in fact incapable of being configured not to do NAT.
This left my parents without working internet. Trying to talk my parents through the mode configuration screens, and then the commands to reconfigure the house server, was not going to work. My only options seemed to be to travel from Cambridge to Northumberland to fix it in person, or to try to find some halfway competent Unix admin in Northumberland at zero notice.
A pub conversation on Thursday led to an alternative strategy. The key observation was that the "item of commerce" that I actually wanted to fix this was a 3G-accessible terminal server and network probe. I had all the ingredients for that in my house: a 3G USB modem, an rpi, and a USB/serial cable.
I spent an hour or so reconfiguring the OS on one of my rpi flash cards to automatically get online via the usb stick, and bring up my vpn, so that I could ssh in. And testing it (and working round a strange EAFNOTAVAIL boot-time race). I shippped the result - all wires at the rpi end already plugged in, including wall wart and long ethernet cable - on Friday morning for Saturday delivery.
On Saturday I talked my mum through where to put the thing (in the hallway where there is mobile phone signal) and the wire (in the house switch). While my parents had lunch I ssh'd into it, got into the house server without trouble, reconfigured it to talk to the new modem, reconfigured the new modem (which thought I was in the house), and fixed up the house server config. About an hour all told.
This all worked very well. Now I just need to make a less-ad-hoc version of the same thing so I can have my 3G stick and that rpi and that rpi install (including its vpn identity) and so on back. The bits are on order. (I don't just want to have my mum send it back until I've replaced it, in case something else goes wrong.)
This left my parents without working internet. Trying to talk my parents through the mode configuration screens, and then the commands to reconfigure the house server, was not going to work. My only options seemed to be to travel from Cambridge to Northumberland to fix it in person, or to try to find some halfway competent Unix admin in Northumberland at zero notice.
A pub conversation on Thursday led to an alternative strategy. The key observation was that the "item of commerce" that I actually wanted to fix this was a 3G-accessible terminal server and network probe. I had all the ingredients for that in my house: a 3G USB modem, an rpi, and a USB/serial cable.
I spent an hour or so reconfiguring the OS on one of my rpi flash cards to automatically get online via the usb stick, and bring up my vpn, so that I could ssh in. And testing it (and working round a strange EAFNOTAVAIL boot-time race). I shippped the result - all wires at the rpi end already plugged in, including wall wart and long ethernet cable - on Friday morning for Saturday delivery.
On Saturday I talked my mum through where to put the thing (in the hallway where there is mobile phone signal) and the wire (in the house switch). While my parents had lunch I ssh'd into it, got into the house server without trouble, reconfigured it to talk to the new modem, reconfigured the new modem (which thought I was in the house), and fixed up the house server config. About an hour all told.
This all worked very well. Now I just need to make a less-ad-hoc version of the same thing so I can have my 3G stick and that rpi and that rpi install (including its vpn identity) and so on back. The bits are on order. (I don't just want to have my mum send it back until I've replaced it, in case something else goes wrong.)
