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Using 802.1s Multiple Spanning Tree Quick Steps for Configuring MSTIs
OmniSwitch 6600 Family Network Configuration Guide April 2006 page 6-17
The following commands assign ports 2/1, 5/1, 5/2, and 3/6 to VLANs 100, 150, 200, and 250 on
Switch B:
-> vlan 100 port default 2/1
-> vlan 150 port default 5/1
-> vlan 200 port default 5/2
-> vlan 250 port default 3/6
5 Create one MSTI using the bridge msti command. For example:
-> bridge msti 1
6 Assign VLANs 200 and 250 to MSTI 1. For example:
-> bridge msti 1 vlan 100 200
By default, all VLANs are associated with the CIST instance. As a result, VLANs 100 and 150 do not
require any configuration to map them to the CIST instance.
7 Configure the port path cost (PPC) for all ports on both switches associated with MSTI 1 to a PPC
value that is lower than the PPC value for the ports associated with the CIST instance using the bridge
msti slot/port path cost command. For example, the PPC for ports associated with the CIST instance is
set to the default of 200,000 for 100 MB connections. The following commands change the PPC value for
ports associated with the MSTI 1 to 20,000:
-> bridge msti 1 4/8 path cost 20,000
-> bridge msti 1 2/12 path cost 20,000
-> bridge msti 1 5/2 path cost 20,000
-> bridge msti 1 3/6 path cost 20,000
Note that in this example, port connections between VLANs 150, 200, and 250 on each switch initially
were blocked, as shown in the diagram on page 6-16. This is because in flat mode MSTP, each instance is
active on all ports resulting in a comparison of connections independent of VLAN and MSTI associations.
To avoid this and allow VLAN traffic to flow over separate data paths based on MSTI association, Step 7
of this tutorial configures a superior port path cost value for ports associated with MSTI 1. As a result,
MSTI 1 selects one of the data paths between its VLANs as the best path, rather than the CIST data paths,
as shown in the diagram on page 6-17.
:
Flat Mode MSTP (802.1s) with Superior MSTI 1 PPC Values
2/1
3/1
4/2
4/8
5/2
5/1
||
VLAN 100
VLAN 250
MSTI-1
VLAN 200
VLAN 150
CIST-0
VLAN 100
VLAN 250
MSTI-1
VLAN 200
VLAN 150
CIST-0
||
2/12
3/6
Switch A Switch B