Re: [Sheflug] Blue Yonder + Linux

[Alex Hudson <nospam [at] alexhudson.com>]

On Thu, Apr 26, 2001 at 07:30:15PM +0100, Mark Broadbent wrote:
> I have used "pump" on the sheffield university net with no problems but then

Ditto. Used pump flawlessly, never had the problems you hear about it.

> From my knowledge of DHCP then this is exactly how it should work according
> the standards that define the DHCP protocol.
> 1. The client (whether renewing or not IIRC) *broadcasts* a request
> 2. Server/s broadcasts a reponse with an offer (of an IP address)
> 3. Client considers the offer/s it has received (there may be more than one
> DHCP server on the network) and then tells each server (via broadcast)
> whether it has accepted/rejected its offer.
> 
> (Don't forget the client doesn't have valid IP address until after step 4)

Were you going to let us in on step 4, or is that a RTFM Mark ? :P

> > > At the moment I have set up in rc.config eth0 to have ip adress 0.0.0.0
> > > subnet 0.0.0.0 and gw 0.0.0.0 and then run  dhclient eth0 manually.
      ^^^^^^^^^^^^^^^^^^^^^ tres terrible!! (do you know what a gateway
                                             is?!!)


Linux has 'interesting' problems with DHCP. Most of it is down to routing.
The usual one is to add a route to 255.255.255.255, something like:

	route add -host 255.255.255.255 dev eth0

(I forget the exact command). Basically, the client needs to listen to
broadcast messages, but for some reason Linux often changes [all ones] to
the local network broadcast address - i.e., 192.168.0.255 or whatever. I'm a
bit hazy on the actual details (as you can probably tell!), but I seem to
recall this is often a source of trouble. Remember, DHCP uses two addresses
- 255.255.255.255 and 0.0.0.0. Many switches do not like these, much
networking headache, ugh....

Ethereal / tcpdump is often quite useful. Anything which will put the
ethernet device in promiscuous mode and let you sniff :)

Cheers,

Alex.
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