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I had a perfectly functioning Ubuntu 12.04 system. I saw a YouTube video from DEFCON where a guy was discussing attacking home routers. In an Internet search of home router security I found a 2011 CERT paper on strengthening SOHO routers. One tip was to reduce the number of IPs on the LAN and to use static IPs.

I went into my 12.04 machine. I set up the static IP address,, that I had prepared at the router and lost Internet access. The LAN still works. When I boot to Windows 7, Windows 7 has Internet access. When I go back to DCHP in Ubuntu, reboot, and check I again have LAN access but no Internet access - different IP [] from DHCP.

I completely reinstalled Ubuntu from a CD - same problem.

I did a search on askubuntu and found 2 previous posts

Wired Internet doesn't work on ubuntu 12.04 from April 29
internet access problem in 12.04 from April 28

I tried those things and they didn't work.

Any ideas, strategies, and tactics for troubleshooting this issue would be much appreciated.

Here are some diagnostics which may be helpful:

ifconfig eth0
eth0      Link encap:Ethernet  HWaddr e0:cb:4e:b1:26:dc  
      inet addr:  Bcast:  Mask: 
      inet6 addr: fe80::e2cb:4eff:feb1:26dc/64 Scope:Link 
      RX packets:1816 errors:0 dropped:0 overruns:0 frame:0 
      TX packets:2168 errors:0 dropped:0 overruns:0 carrier:0 
      collisions:0 txqueuelen:1000 
      RX bytes:162945 (162.9 KB)  TX bytes:162147 (162.1 KB) 

Kernel IP routing table 
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface 
default         UG    0      0        0 eth0 
link-local      *          U     1000   0        0 eth0     *        U     1      0        0 eth0

cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) 

ping -c 4
PING ( 56(84) bytes of data. 
--- ping statistics --- 
4 packets transmitted, 0 received, 100% packet loss, time 3024ms 

The output of nm-tool:
NetworkManager Tool 

State: connected (global) 

- Device: eth0  [Wired connection 1] ------------------------------------------- 
  Type:              Wired 
  Driver:            jme 
  State:             connected 
  Default:           yes 
  HW Address:        E0:CB:4E:B1:26:DC 

    Carrier Detect:  yes 
    Speed:           1000 Mb/s 

  Wired Properties 
    Carrier:         on 

  IPv4 Settings: 
    Prefix:          24 ( 


Results of ping -c 4 PING ( 56(84) bytes of data.

--- ping statistics --- 4 packets transmitted, 0 received, 100% packet loss, time 3024ms

Note: This non-response by the router may be because I have set under Security | Firewall | Attack Check | Respond to Ping on Internet Ports [unchecked]. brings up the router login screen on the laptop running Ubuntu 12.04.

I fixed it. Thank you for your assistance. I really appreciate your input on where to look as I tried to resolve this issue.

I went into the UP|Down arrow Icon on the menu bar. This brings up Network Connections. Under the Wired tab I picked Wired Connection 1 and choose [Edit]. That bring up a new options list with 4 tabs. I choose the 3rd Tab [IPv4 Settings].

Choices Method:Manual Addresses [Add] Address:, Netmask: Gateway: DSN Servers:,, Search Domains: DHCP Client ID: blank - no entry, no change Require IPv4 addressing for this connection to complete: unchecked - no entry, no change Routes - brings up a new options listing [Add] Address: Netmask: Gateway: - I left the 2 check box options blank and clicked OK. Back one screen "Available to all users" [checked] - no change, no entry Save Back one screen to Network Connections | Wired Close

Please excuse me if this fix explanation is too long or detailed. Having searched this resource for answers to questions in the past I know I appreciated when there was more detail. I am new to this forum and don't want to raise the ire of the Sys Admins, Power Users, and the like.

share|improve this question

There are two different settings you need to think about - one is for the IP address, and the other is for the DNS address. Automatic DHCP (default) will set both. Your other choices under the IPv4 Settings tab, are:

Automatic (DHCP) addresses only, which sets the IP addresses via DHCP, but allows you to set the DNS addresses yourself, in case you want to use an alternate such as Google or EasyDNS, etc.

Manual, means you set both the IP address and the DNS address. This may be what you selected, and so you have an IP address, but you cannot use domain names, only IP addresses, to connect out, since DNS translates the names to IP addresses.

Under "DNS servers:" in the IPv4 Settings tab, you can enter any number of DNS addresses, separated by commas. For example, if you wanted to use Google's public DNS servers, you would enter, If you want to use the same ones as your Windows system, you can check them under Windows using "IPCONFIG", or if you have the original Default network profile (you should), you can switch to that, then enter nmcli dev list iface eth0 | grep IP4 at a commandline prompt, and get the DNS addresses (usually 2).

Another way is to look into whether your router can assign static IP addresses. I find this to be easier to maintain.

Also, if you're worried about router security, you can probably simply disable external access completely. Most people never use it anyway.

share|improve this answer

You most likely have an incorrect setting, I'm guessing either your default gateway or DNS server. Please update your question with output from the following:

ifconfig eth0


cat /etc/resolv.conf

ping -c 4
share|improve this answer
That isn't true in 12.04 anymore since it uses dnsmasq now. Paul, please add the output of the following command nm-tool – tgm4883 Jun 13 '12 at 17:38
@tgm4883 - Good call, I removed my comment to reduce confusion. You just get used to some things. Also, thanks for the nm-tool tip. I didn't know about that. paul - Are you sure that is your router's IP address? Please add the results for ping -c 4 to your question. – reverendj1 Jun 13 '12 at 17:43

i had the same issue with mine and finally sorted this out by uninstalling the network manager and putting in the correct dns settings (from the router) into the network configuration file and when i restarted - everything worked fine.

you can try commenting out the settings from the network config file and letting the network manager sort this out with the static ip address and dns server - but this did not work for me.

all the best

share|improve this answer

The only thing that worked for me was:

  • go into modem config (
  • set up DHCP Reservation Lease: it maps LAN IPs to MAC addresses
  • set the interface to use DHCP (the default, modifiable on NetworkManager at nm-connection-editor)

Not sure this will cover your security concerns, but it did give me a working "static IP".

share|improve this answer

In Network Settings > IPv4 Settings, first set ip address manually, boot Ubuntu, then select automatic (DHCP) address only.

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