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For no reason that's clear to me an ubuntu 16.04 machine stopped being able to access the internet. What's curious is that it can still ping the router - but the router cannot ping back! The router is running dd-wrt v3.0-529519 mega. I tried uninstalling and reinstalling Network Manager, which was tricky since apt-get was not working (since no internet access) but no go. ufw is disabled.

ifconfig:

eno1      Link encap:Ethernet  HWaddr 18:66:da:10:81:1c  
          inet addr:10.22.2.160  Bcast:10.22.2.255  Mask:255.255.255.0
          inet6 addr: fe80::3330:9eb0:d72:99c6/64 Scope:Link
          inet6 addr: fe80::1a66:daff:fe10:811c/64 Scope:Link
          inet6 addr: fe80::81fb:97e6:8d6f:2afd/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:97945 errors:0 dropped:4 overruns:0 frame:0
          TX packets:44277 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:39302814 (39.3 MB)  TX bytes:10570496 (10.5 MB)
          Interrupt:20 Memory:f7d00000-f7d20000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:25326 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25326 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:5476236 (5.4 MB)  TX bytes:5476236 (5.4 MB)

tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.22.2.1  P-t-P:10.22.2.2  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP 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:100 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

virbr0    Link encap:Ethernet  HWaddr 00:00:00:00:00:00  
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP 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)

route:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         10.22.2.1       0.0.0.0         UG    100    0        0 eno1
10.22.2.0       *               255.255.255.0   U     0      0        0 eno1
10.22.2.2       *               255.255.255.255 UH    0      0        0 tun0
link-local      *               255.255.0.0     U     1000   0        0 tun0
192.168.122.0   *               255.255.255.0   U     0      0        0 virbr0

iwconfig:

no wireless extensions (on any interface)

I haven't succeeded in installing wireshark yet because, of course, apt-get is not working. I can, though, using dpkg if I can find a download with the right executables in it.Hopefully that will tell us what's going on!

  • Edit your post, and show us ifconfig;iwconfig;ip route. Install and run wireshark. – waltinator Mar 24 '18 at 17:18
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    I'm voting to close this question as off-topic because this is a router firmware problem, not an Ubuntu problem. – Fabby May 1 '18 at 13:22
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I discovered that the problem was because my routers arp cache had no entry for the machine that would not connect. When I manually added it (by using 'arp -s ' on the router itself)I was able to re-connect to the internet. However, when I reboot the router it loses my permanent entry. I believe what's going on is that when the router reboots it sends an ARP request to every machine on the local net, and, for some reason, this particular machine is not responding. I can always re-establish my internet connection if I re-enter that manually added relationship, but clearly something else is wrong. Does anyone have any idea where to look?

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