background image
514 Chapter 14: SNA Topologies
Figure 14-3
Dual Backbones
You can now limit the number of explorers by limiting the hop-count to one hop, because after
one hop they will have arrived at their destination. Clients can now talk to servers or mainframes
that are one hop away but not to clients on other rings, which would be two hops away. To
curtail the explorer replication even further, it is a good idea to give the Token Rings the same
number because an explorer never visits the same ring twice. However, in this situation, the
bridge numbers would have to be different. Confusion would set in if they were numbered
the same.
NOTE
You might want to use a different limit of hop counts for spanning explorers than those of all-
routes explorers. The reason behind this is that mainframes are typically arranged in a
hierarchical fashion, and NetBios servers usually are distributed. As a result, there might need
to be more hop-counts for SNA because there might be more hops to the SNA mainframes than
the hop-counts for NetBios servers, which are probably distributed around the rings.
Token Ring
3
Mainframe
Mac B
Mac A
Token Ring
2
Bridge 1
Token
Ring
1
Bridge 5
Client
Bridge 2
Token
Ring
1
Bridge 6
Client
Bridge 3
Token
Ring
1
Bridge 7
Client
Bridge 4
Token
Ring
1
Bridge 8
Client
IBM compatible
Mainframe
Mac B
Mac A
NetBios server
Netbios server
87200333.book Page 514 Wednesday, August 22, 2001 1:41 PM