Using Bridging Routers To Connect Lans And Networks - Motorola 110502USM001 - Vanguard 60 Router User Manual

Using Bridging Routers to Connect LANs and Networks

Introduction
Operation of
Bridging Router
Bridging and
Routing in the
Vanguard Node
How Vanguard
Bridging Routers
Work
Case 1
Vanguard Routing Model
T0100-01, Revision B
A bridging router is a device in which both bridge and router software run
concurrently. The Vanguard internetworking systems provide bridging router
functions.
Note
For additional information on Bridging, refer to the Bridging Manual
(Part Number T0100-02).
A bridging router handles packets as follows:
• Routes packets if a specific routing protocol is globally enabled.
• Filters packets if you configure specific protocol filters.
• Bridges packets if they are not routed or filtered. In this case, they are
forwarded according to their destination MAC address.
Note that Vanguard support both bridging and routing within the same node for the
same protocol. When using this feature, it is important to configure filters that
disable either routing or bridging between the two end points to prevent packet
duplication.
Bridges work at the Data Link layer providing connectionless service. Routers
operate at the Network layer and, therefore, offer some flexibility in choosing several
network level services.
Vanguard bridging routers examine every packet on a network. The source host
builds a packet from the Application layer downward to the Physical layer and
passes the packet over the network. There can be several different values for the Data
Link (MAC) destination address used with the packet. The Data Link address may
be:
• Addressed to the Motorola internetworking node itself (case 1)
• Addressed to some other node (case 2)
• Addressed as a broadcast packet (case 3)
In case 1, the frame is addressed to the Vanguard internetworking node, as described
here:
• A host sends a frame to the MAC address of the Vanguard node, itself.
• The packet is given to the routing forwarder within the node. The bridging
forwarder is not used in this case.
• The routing forwarder accesses the Network layer that contains the
destination address of the packet.
• The forwarder compares the Network layer destination address to the
addresses in the routing table to obtain the best match.
- If the best match is made, the router rebuilds the Data Link layer and passes
the packet to the next hop.
- If no match is made, the router discards the packet. For IP, an unreachable
packet is transmitted back to the sender.
Using Bridging Routers to Connect LANs and Networks
2-31
Release 5.4