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I noticed networking issues and discovered lo was not behaving properly: it did not have any ip address!

lo        Link encap:Local Loopback  
          LOOPBACK  MTU:16436  Metric:1
          RX packets:3075377 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3075377 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:4224552538 (3.9 GiB)  TX bytes:4224552538 (3.9 GiB)

So I did an ifup lo and then it looks correct:

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:3075440 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3075440 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:4224608530 (3.9 GiB)  TX bytes:4224608530 (3.9 GiB)

What would cause that to happen? NB: I had *not * executed ifdown lo..

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What distributive? If it is Debian, provide output cat /etc/network/interfaces if not check network configuration. –  september Jul 1 '13 at 23:57
1  
You may not have manually downed the interface, but the interface was down. Note the missing "UP" and "RUNNING" from the second line of your first set of terminal output. It's no surprise that it doesn't have even a loopback IP address if it's down. So you need to be asking the question of what could have downed the interface (caused the interface to go down). –  Spiff Jul 2 '13 at 4:10
    
ok i'll ask that question: what would have likely made the interface go down? Now, there are dhcp client issues but that would not likely affect the loopback adapter, correct? –  javadba Jul 2 '13 at 23:35

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