Allied Telesis AT-WL2411 - Manual (Page 79)

AT-WL2411 Installation and User’s Guide
79
If you enable bridging on a remote subnet, a single access point
functions as the designated bridge for the secondary LAN. In this case,
only the designated bridge can establish an IP tunnel. Any other access
point on the remote subnet must attach to the network through the
designated bridge. End device MAC/IP addresses are fully visible on the
remote subnet. If you are using IP tunnels to provide mobility for IP and
other non-routable protocols, you can enable bridging on remote IP
subnets, because IP has built-in safeguards and filters for protecting the
operation of IP routers and other network components.
Also, you should enable bridging if the root access point and the
gateway that supports the NNL devices are on different IP subnets. You
may also need to enable bridging if your wireless end devices use
terminal emulation running the NNL protocol or if you use wireless end
devices that are running both IP and NNL.
Bridging Layer
Functions
Some of the significant functions supported at the bridging layer are
explained below.
Network Organization
Access points automatically configure into a self-organized network
using a spanning tree topology. As devices are added to or removed
from the network, the access points automatically reconfigure to
maintain reliable operation. The spanning tree provides efficient, loop-
free forwarding of frames through the network and allows rapid
roaming of end devices.
The root access point initiates the spanning tree. The root coordinates
the network and distributes common system parameters to other access
points and wireless end devices. The root is elected from a group of
access points that are designated as root candidates at the time of
installation. The election process also occurs in the event of a root
failure. You can configure your network with overlapping coverage so
that the network automatically recovers from any single point of failure.
End devices can optionally participate in the spanning tree protocol by
explicitly attaching to the network. As a result, operational parameters
are easily distributed, unicast flooding is reduced or eliminated, and
roaming hands-off logic is more robust.
Forwarding
The access point maintains a forwarding database of all physical station
addresses, and it knows the correct port for each address. The access
point updates this database by monitoring source addresses on each
port (backward learning), by receiving explicit attachment messages,
and by examining messages exchanged between access points when