Alcatel-Lucent OmniSwitch 6850-48 Network Configuration Manual page 288

MST General Overview
CIST-0
MSTI-2
In the above flat mode MSTP example:
•
Both switches are running in the flat mode and using MSTP.
•
VLANs 100 and 150 are not associated with an MSTI. By default they are controlled by the CIST
instance 0, which exists on every switch.
•
VLANs 200 and 250 are associated with MSTI 2 so their traffic can traverse a path different from that
determined by the CIST.
•
Ports are blocked the same way they were blocked in the flat mode STP/RSTP example; all port
connections are compared to each other across VLANs to determine which connection provides the
best path.
However, because VLANs 200 and 250 are associated to MSTI 2, it is possible to change the port path
cost for ports 2/12, 3/6, 4/8 and/or 5/2 so that they provide the best path for MSTI 2 VLANs, but do not
carry CIST VLAN traffic or cause CIST ports to transition to a blocking state.
Another alternative is to assign all VLANs to an MSTI, leaving no VLANs controlled by the CIST. As
a result, the CIST BPDU will only contain MSTI information.
See "Quick Steps for Configuring MSTIs" on page 12-16
traffic over separate data paths using MSTP.
page 12-6
3/1
VLAN 100
4/2
VLAN 150
4/8
VLAN 200
2/12
VLAN 250
Flat Mode MSTP
OmniSwitch AOS Release 6 Network Configuration Guide
Using 802.1Q 2005 Multiple Spanning Tree
2/1
VLAN 100
5/1
||
VLAN 150
5/2
||
VLAN 200
3/6
||
VLAN 250
for more information about how to direct VLAN
CIST-0
MSTI-2
September 2009