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Recently I see that I often lose internet connectivity on my Linux machines. I am starting to think that it may be a router problem, but I have no idea to check if this is indeed the problem.

Basically what happens is that if I type ifconfig I get the list of all the interfaces, but none of them have an assigned IP address. Even when I use dhclient to pull a random IP address, I still am not able to ping or surf the web.

This is an example of ifconfig output:

eth0      Link encap:Ethernet  HWaddr 08:00:27:b3:da:a1  
          inet6 addr: fe80::a00:27ff:feb3:daa1/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1351 (1.3 KB)  TX bytes:6466 (6.4 KB)

How can I troubleshoot internet connectivity issues? What files do I have to look at?

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  • Are you using IPv6 on your LAN? That interface output shows an IPv6 address but no IPv4 address. – Tim Jul 26 '13 at 13:09
  • @Tim that's right, but I am not using IPv6. I have a Windows machine that uses IPv4 and doesn't have any connectivity problems. – user1301428 Jul 26 '13 at 13:49
  • If the ifconfig output you have listed above is what shows right after you have run dhclient then I would suspect something is wrong with your DHCP server. If DHCP is provided by the router, then try disabling IPv6 support. You could also just try a static IP to determine the source of the problem being DHCP. – Tim Jul 26 '13 at 14:20
  • @Tim for example, now I rebooted the router and I see that a machine has successfully pulled an IP address and Internet connectivity is working. How can I check if DHCP is indeed the problem? – user1301428 Jul 26 '13 at 14:53
  • Lookup how to set a static IP for your distro. Once it is setup and ou reboot or restart networking, wait for a while to see if you have the same intermittent problems with a static IP. If the problems do not arise then it is certainly DHCP being weird. – Tim Jul 26 '13 at 15:01
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After some tinkering with the configuration files I have found out that the problem often involved the routing table. After configuring the route manually the problem was solved.

route add -net 0.0.0.0 netmask 0.0.0.0 gw 192.168.1.1
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