I've looked through other posts with similar issues but so far to no avail. I'm running dual boot with Windows 7 and Ubuntu 15.10 and although the Ethernet connection works on Windows, when I boot Ubuntu it works for a few seconds and then the connection drops. I don't get any notification saying I've been disconnected and the symbol remains the up/down arrows. When I try pinging to a host like Google no host is found. I've disabled Wi-Fi on Ubuntu and tried unplugging/replugging and I get the same issue with working for a few seconds then losing connection.

When I run ifconfig -a I get

enp2s0    Link encap:Ethernet  HWaddr dc:0e:a1:f5:60:20  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::de0e:a1ff:fef5:6020/64 Scope:Link
          RX packets:309 errors:0 dropped:0 overruns:0 frame:0
          TX packets:109 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:42594 (42.5 KB)  TX bytes:13900 (13.9 KB)

lo        Link encap:Local Loopback  
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:246 errors:0 dropped:0 overruns:0 frame:0
          TX packets:246 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:22223 (22.2 KB)  TX bytes:22223 (22.2 KB)

wlp3s0    Link encap:Ethernet  HWaddr 9c:4e:36:17:1f:44  
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

And when I run netstat -rn I get

Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface         UG        0 0          0 enp2s0   U         0 0          0 enp2s0     U         0 0          0 enp2s0

I also tried running sudo arp-scan -I enp2s0 -l to look for duplicate addresses and found none.

I'm still very new to Linux and some network terminologies but any help would be appreciated.

Also to note that the Wi-Fi connection works just fine. It's just the wired connection that is having problems.

  • What is your ethernet card? (lspci). Any relevant log messages? – vonbrand Jan 8 '16 at 0:13
  • If you run tcpdump after things break, do you see any traffic on the interface? – Mark Plotnick Jan 8 '16 at 2:37
  • Ethernet controller is Qualcomm Atheros AR8161 Gigabit Ethernet. No log messages when it breaks. I get an Operation not permitted message when I use tcpdump – Bert Jan 8 '16 at 3:09
  • My bad I didn't run it with sudo, I repeatedly get "22:15:52.977713 ARP, Request who-has tell, length 28" when I run tcpdump. – Bert Jan 8 '16 at 3:17

Try setting your Wired MTU to something really high (like >8192) - I know there was a bug for some Atheros cards (especially AR8161). This is a temporary solution though, and doesn't fix the issue, just postpones it. I am working on a patch for Ubuntu 16.04 - will let you know if fixed :)

  • 1
    Setting it to 8192 bytes worked for me! At first I cannot believe it---it worked like a charm! You might want to point out to novices how to set MTU (go to Network Manager -> Edit Connections -> Ethernet -> MTU) – Xin Aug 29 '16 at 8:23

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