IBM Nortel Networks L2/3, Manual

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Nortel Networks L2/3 Ethernet Switch Module for IBM
Eserver
BladeCenter
spanning tree instance is associated with one or more VLANs, which must be explicitly
identified as part of the configuration. It is good practice to associate VLANs with the same
topology to a single instance of spanning tree. This reduces processor overhead on the
GbESM and other switches in the network and it reduces the traffic generated by the BPDUs
that the switches send to each other.
In general, MSTP configuration mirrors the configuration of multiple instances of classic
802.1D spanning tree which is described in 7.7.2, “Common Spanning Tree configuration -
IEEE 802.1D and PVST” on page 84, except as follows:
򐂰 When multiple 802.1D instances are used to interoperate with Cisco PVST+, there is
typically only one VLAN associated with each Spanning Tree Group (STG). When MSTP
is used, both the GbESM and any upstream switches from any vendor must explicitly
identify the VLANs associated with each MSTP instance.
򐂰 MSTP requires the configuration of a region name and revision number which
must
match
for all switches if they are to recognize each other as part of the same MSTP region. In
almost all cases, GbESMs should be in the same MSTP region as their upstream
neighbors.
򐂰 MSTP can recognize and interoperate with switches running 802.1D (classic spanning
tree) or 802.1w (rapid spanning tree). The commands under /c/l2/mrst/cist define the
parameters for this interoperability. These commands also govern the interactions of
boundary switches which are neighbors but are part of different MSTP regions.
The MST functionality is enabled on the GbESM by the following commands:
/c/l2/mrst/on
Enables 802.1w or 802.1s (rapid and multiple
spanning tree) functionality
/c/l2/mrst/mode mstp Selects multiple spanning tree (802.1s) instead of
single rapid spanning tree (802.1w)
/c/l2/mrst/cist Menu of commands to configure the common
spanning tree defined by 802.1s, which is equivalent to
spanning tree group 0 (zero).
/c/l2/stg <group number> Menu of commands to configure additional instances
of MSTP. This includes commands to specify bridge
parameters, port parameters, and to identify the
VLANs associated with this spanning tree group.
/c/l2/stg <group number/on|off Enables or disables a spanning tree instance.
Key configuration commands to verify MSTP
On the GbESM, the /info/l2/stg command shows the status of the MSTP instances when
MSTP is in use. It presents output as shown below. Note that the common internal spanning
tree is instance 0 (zero) and is used to communicate outside of the MSTP region. Its details
are obtained by the /info/l2/cist command.
Example 7-17 MSTP Information Display - GbESM
>> Main# /info/l2/stg
------------------------------------------------------------------
Spanning Tree Group 1: On (MSTP)
VLANs: 10 30
Current Root: Path-Cost Port Aging
1000 00:12:7f:ea:76:00 20000 EXT1 300
Parameters: Priority Aging