DNS & Firefox fails on Linux, WindIE works only on older windows OS, ex not Vista

Hal Burgiss hal at burgiss.net
Sun Apr 25 14:38:46 UTC 2010

On Sun, Apr 25, 2010 at 1:07 AM, giovanni_re <john_re at fastmail.us> wrote:
> I'm trying to get a Linux (KUbuntu) laptop with Firefox working on a network, INet supplied probably by ATT (The USA national phone company) DSL. It has a router/gateway, maybe including a firewall, about 3-6 yrs in place, which I can't physically access.
> Under Linux, it gets an IP assigned (either automatically, or with dhclient? ifup eth0?), but dig & nslookup fail. Can ping the gateway. Ping offsite IP = untried.  Firefox fails to bring up web pages, IIRC because unable to look up host name.

1. Don't use FF for network diagnostics. It can't do them. All this
tells you is something isn't working right.

2. If you have a legit looking IP address (and not something like, then possibly all is well except DNS configuration. This
can be tested by pinging an external IP address:

  ping -n -c1

If that succeeds, you should be able to solve it by manually setting a

  sudo echo "nameserver" >>  /etc/resolv.conf

(this is google's open nameserver).

OTHO, if that ping did not work, and you have a legit IP, then you
might have a routing table problem. That can be examined with:

  route -n

Should look something like:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface   U     0      0        0 eth0     U     1000   0        0 eth0         UG    100    0        0 eth0

The last line there is the "default" route, which is critical and
should correspond to the router's internal IP. If the IP you have
(shown with ifconfig) is on the same subnet, and the routing table is
fubar, you can manually set it using the 'route' command (see man page
for default route command).

Other useful commands:

 arp -a
 sudo traceroute -n

Also, some early DSL implementations required the client system to
have a working PPPoE client installed. This can be done on Ubuntu, but
surely is off by default. I wouldn't worry about this, unless all else

If you have nmap installed (or have the ability to install it), you
can see what ports are open. DCHP server is port 67 UDP:

$ nmap -p67 -sU

Starting Nmap 5.00 ( http://nmap.org ) at 2010-04-25 10:33 EDT
Interesting ports on zoom (
67/udp open|filtered dhcps
MAC Address: 00:40:36:31:8C:F2 (Tribe Computer Works)

Nmap done: 1 IP address (1 host up) scanned in 0.63 seconds

As mentioned, nmap is quite handy and can do a lot more.


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