Mac Forum / General / Hardware / September 2008

I have a WDS setup at home involving an Airport Extreme and two Airport
Express units. I've set up a WDS containining just Main and Remote base
stations. (I tried to set up a Relay once and it didn't work, but after
reading the documentation just now, I think I know where I went wrong.)

All base stations must be set to "Participate in WDS".

There can be only one Main WDS station. This is the one which has the
Internet connection and should be located as centrally as possible.

A Remote base station can be used to connect wireless or Ethernet
clients to the network, and provide other services such as printer
sharing or audio output. It connects wirelessly to one other base
station.

A Relay base station can do everything that a Remote can do, plus it is
able to connect wirelessly to two base stations so it can forward data
between them.

Every Remote or Relay base station on the network must be configured to
use the same wireless network settings as the Main base station
(frequency, channel, network name and password). In addition, they need
to be configured with the MAC address (Airport ID) of the Main base
station (in the "WDS Main" field).

The Main base station also needs to be configured with the MAC address
(Airport ID) of each Remote or Relay which will connect directly to it
(in the "WDS Remotes" field).

If you network is small enough and all the other base stations are able
to talk to the Main base station, then you don't need any Relay
stations. Configure all other base stations as Remotes.

You only need to use a Relay if one or more of your Remote base stations
is unable to get a good signal from the Main base station. In that case,
you will need one base station configured as a Relay which is located
somewhere between the "distant Remote" and the Main base station.

On the Relay, the "WDS Remotes" list should include all the Remote base
stations which are supposed to use that relay.

The "WDS Main" field for both the Relay and Remote is the MAC address of
the Main station. (That's the bit I got wrong - I told the Remote to use
the MAC address of the Relay as if it was the Main, and the whole
network stopped working.)

The "WDS Remotes" list for each base station should only include Remote
or Relay base stations which connect directly to that base station.

For example, if your network looks like this:

Office (Main) ------ Lounge (Relay) ------ Dining (Remote)

then your "Office (Main)" should be configured with the MAC address of
"Lounge (Relay)" in its list of remotes, and "Lounge (Relay)" should
configured with the MAC address of "Dining (Remote)" in its list of
remotes. Both "Lounge (Relay)" and "Dining (Remote)" are configured with
the WDS Main as "Office (Main)".

In principle this can be extended to more complex networks which need
multiple Relays to connect between a distant Remote and the Main base
station. This should be configured so that each Remote and Relay is only
listed once in either the Main or one other Relay's "WDS Remotes" list.
This ensures a "directed graph" of connections, radiating out from the
Main, via one or more Relays and ending at one or more Remotes.

I'm not sure what will happen if you list a Relay or Remote in more than
one other base station's "WDS Remotes" list. This might allow for
alternative connection paths should there be varying signal strength,
but if relays are involved it might also result in forwarding loops or
lost data which could stop the entire network or part of it from
functioning.

I'd rather use a configuration with the least chance of misbehaving, so
only list each Remote or Relay in one other Relay or the Main.

The "WDS Main" setting must be the same for all Relay and Remote base
stations. It is the Airport ID of the Main station.

The "WDS Remotes" list for each base station only lists the Airport IDs
of other "more distant" (relative to the Main) base stations which
connect directly to this base station. (I think.)

I observed this with my network - the speed drops to 54 Mbps if I use
WDS.

If you want to use 802.11n, there is a separate mechanism, which is
easier to set up. On the primary base station, choose "Create a wireless
network" and turn on the "Allow this network to be extended" option. On
each other base station, choose "Extend a wireless network". (You might
also need to "allow this network to be extended" on go-between stations
- I don't have one handy to see if that setting is available.) You don't
need to enter any MAC addresses.

802.11b/g base stations cannot participate in this sort of wireless
network, and it might also exclude 802.11b/g clients. (I haven't tried
it in anger yet.) If so, and you need to support older clients, you
would need a parallel network of 802.11g base stations (which would be
connected to the main base station at a single point via Ethernet).