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I've just upgraded one of my systems from 12.04 to 12.10. Now I can't connect on that system beyond my local network. Connections within the local network seem to work fine, and I can make nonlocal connections from other machines (like the one I'm asking this question from). I suspect that some routing information has been messed up, but I don't know where to look for it. It's not a nameserver problem -- pinging outside sites by their IP addresses doesn't work either.

I have another laptop next to this one, also running Kubuntu 12.10. On the one that can't connect, arp produces no output. On the other one, it produces ether 00:23:69:fa:ce:ae C wlan0

On the working machine, the output of netstat starts with some tcp entries. On the nonworking one, those entries are absent.

I asked this question on the Ubuntu forum but haven't gotten any answers there. One further complication: since the troublesome machine has no outside connection, it's extremely difficult to download anything to it.

For what it's worth, "ping" produces "connect: Network is unreachable".

Update: after a lot of fiddling, I have my external world back. I don't know what the key action was, but the first indication of progress was that "ping" worked. At that point I still didn't have a working nameserver, so external URLs didn't work. But I did this (based on an online post, of course):

sudo dpkg-reconfigure resolvconf

and answered Yes to all prompts. That did the trick!!

Apparently my problem was unique, or close to it, since I couldn't find any online references to it: local net working, remote net not working, including explicit IP addresses. So I suppose that if no one else has this problem, no one cares about the solution!!

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Your problem is unfortunately not unique. See – jdthood Dec 4 '12 at 12:05

I was (and am) having a similar problem while connecting to the Internet using my MTS MBlaze (India) dongle which is a ZTE device. I am using Kubuntu 12.10.

A while back I was only able to connect to the device from Network Manager applet, but a ping to any address including resulted in "Network is unreachable". I figured out this could primarily be because of my host not being able to connect to MTS gateway.

ifconfig shows something similar to the following:

ppp0      Link encap:Point-to-Point Protocol  
          inet addr:  P-t-P:  Mask:

I used the route command to manually add the gateway address (P-t-P in above ifconfig output) as follows:

sudo route add default gw

And voila, I was able to ping again, even to (as dongle devices auto configure DNS servers as well); there is no need to change /etc/resolv.conf at all.

Now I need to figure out how to automate this. Any help most welcome.

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I had the same problem... I know you said that it's not a nameserver problem, but changing the nameserver entry in /etc/resolv.conf from loopback address to did the trick for me.

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Note that editing /etc/resolv.conf by hand is deprecated in Ubuntu 12.04 and later. You should do it the resolvconf way instead. – jdthood Dec 4 '12 at 12:03
Good info, Mahalo. – I-Ii Dec 4 '12 at 22:54

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