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Switch Overview SmartStack STS16-20D/STS16-20R Token Ring Switches Installation and User Guide
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The bridge relay function has a single bridge number and multiple ring
numbers (one per logical ring)
SRS is used between the ports of each logical ring. The bridge relay function runs
the IBM Spanning Tree Protocol to eliminate parallel paths with other source-route
bridges. The IEEE 802.1D Spanning Tree Protocol is still used with each logical
ring. Duplicate MAC addresses are allowed
only
if they are on different logical
rings.
Source Route Transparent (SRT)
The BRF can combine transparent switching with source route bridging. Non-
source-routed packets are switched across logical rings by transparent bridging.
Source-routed frames are switched across logical rings by source route bridging
and within each logical ring by source route switching.
The bridge relay function runs the IEEE 802.1D Spanning Tree Protocol. Duplicate
MAC addresses are
not
allowed.
SRT/SRB
This is a special mode combining SRT and the SRB switching modes. Each logical
ring will operate either in SRT mode or in SRB mode. Transparent bridging will
only take place between logical rings in SRT mode. Source route bridging will take
place between all logical rings.
The purpose of the SRT/SRB mode is to allow duplicate MAC addresses to be used
when in SRT mode. The ports on which the duplicate MAC addresses reside can be
reached only by source routing.
The bridge relay function runs the IBM Spanning Tree Protocol on the SRB logical
rings to eliminate parallel paths with all source route bridges. It runs the IEEE
802.1D Spanning Tree Protocol on the SRT logical rings to eliminate parallel paths
with other SRT bridges. The two resulting spanning trees are joined together.
The IEEE 802.1D Spanning Tree Protocol is still used to eliminate parallel paths
within each logical ring whether it is SRB or SRT.
The benefit of the SRT/SRB mode is that it allows part of the network to be run in
SRT mode to accommodate applications that do not support source routing, while
still supporting duplicate MAC addresses on a number of SRB ports (for example,
for SNA gateway applications).