Local-Area Networks and LAN Switching - CCIE Routing and Switching Exam Certification Guide - page 141

The RIF field in hex is 0830.014c.003a.0100.

The CCIE candidate should know how to read and construct the RIF field for regular SRB and
in other scenarios, such as RSRB and DLSw. RIF examples are included in each corresponding
section.

SRB Configuration with Cisco Routers
SRB is limited in that it is a flat network topology in the data-link layer. Another limitation is
the maximum hop limitation of 7 bridges. Routers can be introduced into the network to help
limit the number of hops on the network. Remote Token Ring networks can be attached to rout-
ers to reduce bridge hops. This is accomplished with the concept of the virtual ring, as seen in
Figure 4-24. Consider each router interface a minibridge that connects the external ring to the
internal virtual ring. You use the ring number in the RIF field just like any other physical ring.

SRB Configuration

Figure 4-24

Traffic from Ring 1 to Rign 3 flows through bridge 10, then Ring 5, and finally bridge 12.

source-bridge ring-group 5
(virtual ring 5)

Router

interface tokenring 0
source-bridge 1 10 5

1 5 3

10 12

interface tokenring 2
source-bridge 3 12 5

11

interface tokenring 1
source-bridge 2 11 5

2

To configure the virtual ring group, use the global command source-bridge ring-group virtual-
ring-group-number . Each Token Ring LAN is bridged to the virtual ring by using the interface
command source-bridge ring-number bridge-number virtual-ring-group-number. The bridge
number can be from 1 to 15. The ring number is from 1 to 4095.

The configuration for the router in Figure 4-24 is displayed in Example 4-7.

Configuration Example of Source Route Bridging Example 4-7

source-bridge ring-group 5
!
interface tokenring 0
source-bridge 1 10 5
source-bridge spanning

continues