
Using Source Routing Bridge Services
114060 Rev. A 2-3
Figure 2-2. Source Routing Designator
After the bridge adds the routing designator, the other bridges send the frame out
all ports (floods the frame). As a result, multiple copies of the same ARE frame
can appear on a LAN, and the frame recipient can receive multiple copies of the
frame (one copy for each possible path through the extended network).
Each ARE frame received by the destination endstation contains a unique
sequenced list of routing designators tracing the frame’s path through the source
routing network.
Spanning Tree Broadcast Routing
An endstation configured for spanning tree broadcast routing generates a single
frame that follows a loop-free path from source to destination. This frame is a
spanning tree explorer (STE).
When an endstation generates an STE frame, each bridge on the spanning tree
forwards the frame onto all active (nonblocked) ports, except the port that
received the frame. With spanning tree broadcast routing, one copy of the STE
appears on each LAN and the frame recipient receives a single copy only.
Note: In a looped topology, the originating bridge may receive the ARE
frame; the originating bridge discards the frame.
001A 100A 0020 data...
Incoming Ring ID
Internal LAN ID/Bridge ID
Outgoing Ring ID
BRG0012A
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