Allied Telesis AT-WA7500 - Manual (Page 121)

AT-WA7500 User’s Guide
121
How Frames
Are Forwarded
Through IP
Tunnels
The access point maintains a forwarding database of all MAC addresses,
and it knows the correct port for each MAC 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 end
devices roam. The database also includes the power management status
of each end device, which allows the access point to support the
pending message feature of the network. The forwarding database
allows the Ethernet bridging software to make efficient forwarding
decisions.
Any frame that is sent through an IP tunnel is addressed to the unicast IP
address of the access point at the other end of the tunnel. An access
point at the remote end of the tunnel learns the unicast IP address of the
root access point by listening to IP hello messages. The root access point
learns the unicast IP address of a remote access point when the access
point attaches to the network.
Outbound Frames
Frames are forwarded outbound (to a secondary LAN) through an IP
tunnel if:
‰ an end device is known to be attached to an access point on a
remote IP subnet.
‰ the frame type is configured to pass.
IP and ARP frames are never forwarded outbound through an IP tunnel
unless the destination IP address belongs to the root IP subnet. Usually,
these frames are destined for wireless end devices that have roamed
away from their root IP subnet.
Unicast frames are not flooded. Unicast frames are only forwarded
outbound through an IP tunnel if the destination address identifies an
end device that has roamed to a remote IP subnet. End devices attach to
the root access point, which maintains entries for these devices in its
forwarding database. The database entries indicate the correct subnet
for outbound forwarding.
For TCP/IP applications, IP and ARP frames must be forwarded through
IP tunnels. An IP or ARP frame is only forwarded outbound if the
destination address identifies an end device on the root IP subnet.
Usually, ARP requests (which are multicast frames) that originate on the
root IP subnet are forwarded outbound to all devices on the network,
including through IP tunnels to remote IP subnets. However, if you
enable ARP flooding, ARP frames are only sent through the IP tunnel to
the destination end device.