DHCP setup

I'm not sure what you're trying to do, but I take it your DHCP is not being
relayed to the wireless clients. Most wlan ap's have got an option called
DHCP relay somewhere in their config menu, some have this enabled by
default. or am i just talking crap.. sorry 3am




Coenraad Loubser

Hello all,

I'm still working on setting up a DHCP server for a W-ISP but I'm
running into a problem.

The wireless equipment that I'm using is a Tranzeo CPE to a Tranzeo 4500
series AP. On the linux server, when I type 'ip neigh' it shows the IP
address of the computer behind the CPE (the CPE is essentialy a wireless
bridge) and the MAC address of the CPE itself NOT the actual computer.
The MAC address of the computer is not shown anywhere so it is my
assumption that when a packet comes from the CPE, the CPE changes the
MAC address in the ethernet header to that of the CPE.

But, when a computer sends a discover packet, it seems to include the
MAC of the computer itself and dhcpd disregards the MAC in the ethernet
header. Is there a way to make dhcpd look at the MAC in the ethernet
header instead of the one included in the discover paket? Or am I
misunderstanding the protocol?

Thanks in advance,
Kevin Brown.

Kevin Brown wrote:
> Hello all,
>
> I'm still working on setting up a DHCP server for a W-ISP but I'm
> running into a problem.
>
> The wireless equipment that I'm using is a Tranzeo CPE to a Tranzeo
4500
> series AP. On the linux server, when I type 'ip neigh' it shows the
IP
> address of the computer behind the CPE (the CPE is essentialy a
wireless
> bridge) and the MAC address of the CPE itself NOT the actual
computer.
> The MAC address of the computer is not shown anywhere so it is my
> assumption that when a packet comes from the CPE, the CPE changes the

> MAC address in the ethernet header to that of the CPE.

I'm a bit confused here (not the first time. Sounds like the CPE is
a router/bridge of some sort -- ie., IP of "computer behind CPE" is
what? A router? The AP? Another host computer on the same net
segment? If the CPE is a true switch, it should not touch/mangle the
ethernet frame at all.

But if the CPE is a router/bridge gizmo then all IPs (ARP replies) that
come through the CPE will associate those IPs with the MAC of the CPE
-- just as my solo host shows all IPs associated with my default GW's
MAC. The MAC relates to and has meaning only on a local physical
segment, either another host or a router.

> But, when a computer sends a discover packet, it seems to include the

> MAC of the computer itself and dhcpd disregards the MAC in the
ethernet
> header. Is there a way to make dhcpd look at the MAC in the ethernet

> header instead of the one included in the discover paket? Or am I
> misunderstanding the protocol?

Hmmm...

Not familiar with your equipment and I'm not clear on your setup/layout
re: Linux dhcp server <-> Transzeo CPE <-> clients. Ie., I'm not
really sure of the packet path.

But...

DHCP will never see the ethernet frame -- it's already stripped off.
The MAC in the IP/DHCP packet is just used to identify the host getting
the address. It is not used for moving/routing packets in any way.
That's what the arp cache (and ARP requests/replies) is for. This is
why your "ip neigh" shows the MAC of the CPE -- it _is_ used to move
packets evidently (and so the CPE must not be "just" a switch).

Quick google for something on the Transzeo does show "manual tweaking"
required to keep clients connected though.

hth,
prg