[YLUG] Interesting Networking Problem

[Matthew Bloch]

On Monday 08 May 2006 00:58, Njal Munro wrote:
[snip]
> This laptop is asigned a ip from a DHCP wireless router, i cannot change
> the fact it's assigned by DHCP, it's not my router, it's a uni house.
> However once the laptop is assigned it's IP on wireless interfact (eth0)
> it should share it's connection with the Desktop via an ethernet cable
> (eth1) the laptop's eth1 connects to the desktop's ethernet (eth0) and
> both SHOULD be on the internet.
>
> The laptop's eth1 port is assigned the static IP 192.168.0.1, the
> desktop's eth0 is assigned 192.168.0.2 it's gateway is assigned as the
> laptop's IP, and the DNS info was copied from my laptop to my desktop
> propery, now the desktop run's fedora 5.

Hi Neil, this sounds like you're asking for trouble assigning IP ranges in the 
same range to different interfaces!  If it worked before I wouldn't like to 
guess how :)

I'd suggest in this situation turning the laptop's eth0 and eth1 into a 
single "bridge" interface.  You didn't mention what distro the laptop was 
running but from a standing start where the laptop hasn't got either 
interface configured, this ought to work:

ifconfig eth0 down
ifconfig eth1 down
brctl addbr br0
brctl addif br0 eth0
brctl addif br0 eth1

The laptop can then set up interface br0 as normal (e.g. run "dhclient br0") 
which acts exactly the same as eth0 did.

The desktop can then have a simple dhcp configuration as well, and get its IP 
direct from the router rather than have the laptop work as a router.

Let me know if you need any more of a hand with this -- as I said I can't 
really guess how it might have used to work but it doesn't sound like an 
entirely healty IP configuration.  This way your laptop acts as a simple 
wireless to ethernet bridge, and the desktop doesn't need to be aware of its 
presence.

-- 
Matthew