Install guide

26 Bridging Enhancements Release Note
Software Version 2.9.1
C613-10486-00 REV C
Bridging Enhancements
This Software Version includes the following enhancements to Bridging:
■ VLAN to WAN Bridging
■ Retaining or Stripping VLAN Tags
This section describes the enhancements. The new and modified commands to
implement them are described in Command Reference Updates.
VLAN to WAN Bridging
Software Version 2.9.1 includes the ability to bridge between VLANs over a
PPP WAN link.
In general, it is better to route a protocol than to bridge it. However, sometimes
bridging is a more appropriate solution, particularly where unroutable upper
layer protocols are used. These protocols sometimes produce high levels of
broadcast messages that can overload a network, an effect that gets
progressively worse as the number of devices increases. Although this
situation may not pose a problem to the high bandwidths available on local
area networks, it could heavily congest the more limited bandwidths available
on wide area links. This effect can be reduced by adding a VLAN to a bridge
and then limiting the VLAN to devices that require wide area connections. The
remote VLAN bridge is able to support up to 16 VLANs.
Internal Representation of the VLAN-to-WAN Bridge
The router contains both a switch module and a bridge module. This section
explains how these modules provide the learning and forwarding functions for
the VLAN-to-WAN bridge.
Figure 3 shows an internal representation of the VLAN-to-WAN bridge that
exists on the AR400 and AR700 Series routers. Note that the bridge and switch
symbols are internal functional representations and are not standalone devices.
Figure 3: Internal representation of the switch’s VLAN-to-WAN bridge
BRG7_R
Single
Virtual
Port
Internal
Connection
VLAN A
Switch
Forwarding
Database
Bridge
Station
Map
Switch
Module
Switch Ports
Switch Ports
VLAN B
Bridge
Module