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Reliable SNA Internetworks 513
Figure 14-2
Dual FEPs
Dual-Backbone Token Ring Design
Dual-backbone Token Ring design is another common technique used in IBM environments.
Remember that the basic mechanic of source route bridging is explorer control. Because an all-
routes explorer takes every possible path through a network, you will have explorers
multiplying in the network if you are not careful with your design.
Figure 14-3 depicts a practical design for controlling explorers. Start with a dual Token Ring
backbone. In Figure 14-3, the mainframes are connected to the backbone rings (the vertical
rings in this example). Servers are also attached to the backbone rings in most cases. Clients
reside on the horizontal rings.
IBM 3720/25/45
LAAs applied here
DSPU or gateway
DSPU or gateway
FEP left
FEP right
Host 1
Host 2
Host 3
Host 4
Token Ring
10
Token Ring
20
Token Ring
30
Token Ring
40
87200333.book Page 513 Wednesday, August 22, 2001 1:41 PM