Vanguard Routing Model
2-33
T0100-01, Revision B
Release 5.4
Using Bridging Routers to Connect LANs and Networks
Using Bridge and
Router Filters
Figure 2-20 shows an example of a network where filtering is used.
Figure 2-20. Using Bridge and Router Filters to Control Network Traffic
Figure 2-20
Explanation
Figure 2-20 is explained here:
• Several smaller LANs (LAN 2, 3, and 4) have stations that communicate with
stations on LAN 1 and with other stations in the network (not shown).
• Bridging is used in the lower part of the network because only direct
communications to a main LAN are available and there is no need for the
overhead of running a RIP protocol (except in node N3).
• Connections are provided by nodes N1 through N4 and other nodes that
function as bridges and routers or bridging routers.
• Stations S2 and S4 communicate with station S1 by bridging, since nodes 2 and
4 provide only bridging.
• For stations 2 and 4 to communicate with other remote stations, the traffic is
bridged to node 1, and from there it is routed to the destination.
• Station S3 can be set up to either bridge or route to stations on LAN 1, but not to
both simultaneously (for example, bridge to station S1 and route to station S5).
• For node 3, you can either bridge between LAN 3 and LAN 1, or route. The
decision can be policy based or derived from traffic considerations.
• Routing is used, stations on LAN 3 can route to all other stations in the network
and should select bridge protocol filters to block IP traffic on bridge links going
from LAN 3 to LAN 1. This allows full routing for IP traffic and bridging for
other protocols.
S5
Router
Router
Router
Bridge,
Router
S1
Bridge,
Router
Bridge,
Router
Bridge,
Router
S2
S3
S4
LAN 2
LAN 3
LAN 1
LAN 4
N1
N2
N3
N4
