help needed for Ubuntu 8.04 on HP 6720s notebook

[Brian McKee]

On Wed, Sep 10, 2008 at 10:47 AM, Abhishek Bawkar
<abhishek.linux4me at googlemail.com> wrote:
> Hey Brian,
>
> Thanks for your tip, I thought of giving your suggestion a try that,
> changing the subnet mask to 255.255.0.0 and finally it worked. I am happy
> now. Now I hope I'll be able to do everything. Thanks once again.
>
> Would like to understand how it worked. Subnet mask in Windows was
> 255.255.255.0 and in Linux it is 255.255.0.0, could not understand. Can you
> please explain or give a link where I can read?

Well, I can't really explain it fully as I'm not 100% sure what
exactly is going on.

Your 'ISP' so to speak is doing some odd things.

First off - 100.100.x.x series numbers shouldn't really be used behind
a NAT.  It's not 'correct' and could cause issues in some cases I
imagine.

Secondly, I note sure why it work in Windows with those settings.
It's possible your ISP has some stuff in place that 'fixes' the wrong
setting so it works without you doing anything.

I believe I heard that Windows might dump things out the default
interface if it hasn't got a route to it's default gateway.  (Don't
quote me on that - I'm not a Windows networking guru)  That might
explain why it works for you as well.

Are you really really sure those are the settings you have in Windows?

To get started on understanding all this stuff, there's a million hits
in Google on 'subnetting' and learning TCP/IP.
<http://www.google.ca/search?q=subnetting+explained&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a>
I don't have a particular one handy I think is good or easy to follow.

If you like, you could try this podcast series
http://www.grc.com/securitynow.htm
Way back when they started they did some basic networking stuff like
this episode
http://media.grc.com/sn/sn-027-lq.mp3

The short version is the subnet tells the computer what's 'local' and
what has to go out through the 'gateway'
Your original settings said the gateway was at an address that wasn't
local, so it had no idea where to send things.
In other words - in other words, as far as Linux was concerned 'you
can't get there from here'

The less restrictive subnet mask told it the gateway was local - just
dump it on the LAN and it'll answer.

DHCP does make it easier for clients - then it's the server's
responsibility to provide the right info.

HTH

Brian