[ubuntu-za] network problem

Robert Schumann robert at cantab.net
Tue May 9 23:15:16 BST 2006

On Tue, 2006-05-09 at 23:20 +0200, Dimitri Mallis wrote:
> hi list, 
> i was having troble with my network, but i could conect to the
> internet. then i changed something, then i was able to browez the
> network. when i rebooted i could not connect to the internet :<
> pppoe -> sais it connected 
> what is lo ?  Local Loopback -> was never there before

>From Wikipedia: A loopback is a communications channel with only one
endpoint. Any message transmitted through such a channel is immediately
received by the selfsame channel.

lo, the loopback interface, is (close your eyes now if you don't want
the geek explanation) what client/server protocols on the same system
use to speak to each other.  Loopback is not your problem, and I'd be
worried if it *wasn't* working.

> that was never there before. how can i get rid of that. i think that
> is were my problem is.

I suspect the problem may be with routing.  You can type "route" at the
command line (or use the gnome-network-tools item from your System menu,
I think) to see which interface is used to send information out. On my
computer it says

[rewley at everland: ~] route
Kernel IP routing table
Destination  Gateway      Genmask       Flags Metric Ref Use Iface U     0      0   0   wlan0       UG    0      0   0   wlan0

which means that, to reach the outside world, packets must be sent to my
wireless interface wlan0.  If your default ( interface is eth0,
as I suspect, then packets are being spewed out of your ethernet
interface and thus not making it to the internet.

If you're feeling intrepid, you could fix routing problems by following
the instructions on the man page for route - some command like "route
add default ppp0" - without editing or restarting anything.

You can fix it by disabling eth0 (either using the network configuration
tool from the menu or by editing /etc/network/interfaces) and then
restarting your network ("sudo /etc/init.d/network restart" or however
you do things - perhaps just restart).

I may be wrong, but let us know what route says, and for good measure
also what "arp -n" outputs.  The gurus on this list might be able to
tell you how to configure routing the right way.


> OR
> how can i delete ALL my network & internet settings & then reconfigure
> everything? 
> root at ubuntu:~# pppoe-start
> ......... Connected!
> root at ubuntu:~# ping www.google.com
> ping: unknown host www.google.com
> root at ubuntu:~# ifconfig 
> eth0      Link encap:Ethernet  HWaddr 00:50:70:26:01:46
>           inet addr:  Bcast:  Mask:
>           inet6 addr: fe80::250:70ff:fe26:146/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:148 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:200 errors:0 dropped:0 overruns:0 carrier:0 
>           collisions:0 txqueuelen:1000
>           RX bytes:14932 (14.5 KiB)  TX bytes:14823 (14.4 KiB)
>           Interrupt:23 Base address:0xc000
> lo        Link encap:Local Loopback
>           inet addr:  Mask:
>           inet6 addr: ::1/128 Scope:Host
>           UP LOOPBACK RUNNING  MTU:16436  Metric:1
>           RX packets:30 errors:0 dropped:0 overruns:0 frame:0 
>           TX packets:30 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:1500 (1.4 KiB)  TX bytes:1500 (1.4 KiB)
> ppp0      Link encap:Point-to-Point Protocol
>           inet addr:  P-t-P:
> Mask:
>           RX packets:4 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:3
>           RX bytes:102 (102.0 b)  TX bytes:61 (61.0 b)
> root at ubuntu:~#

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