HP 200 Series Services And Applications page 73

Bridging Service
Source-Routing Bridging
How Source Routing Works
Source routing networks consist of LAN segments interconnected by source
routing bridges. Each LAN segment has an identification number unique
throughout the network, called a LAN ID, and also called a ring number or
ring ID. Each source routing bridge has an identification number; the source
routing bridge is always (by default) bridge ID number 1. Additionally, each
source-routing bridge has an internal LAN ID number unique throughout the
network.
As a source-routed frame traverses the network, it collects a sequence of
routing designators that track its path through the network. Every source-
routing bridge that the frame passes through inserts routing designators in
the frame's MAC header. Transparent bridges, however, do not write to the
MAC header. Each routing designator pairs a LAN segment number with a
bridge ID number in order to identify a portion of the frame's path through
the bridge.
Bridge ID 1
LAN ID 5
LAN ID 8
Router
Incoming Path Internal Path Outgoing Path
Figure 11. SRT Bridge Routing Designators
In figure 11, the router receives the source-routed frame on LAN segment 5
and relays the frame on LAN segment 8. Consequently, the router adds three
routing designators (5-1, A-1, 8-0) to the frame's MAC header. Figure 12
illustrates how these routing designators map the frame's path through this
router.
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