Dell 6200 manual Admin Port State, MSTP Port State, Active Topology, April

MSTP INTEROPERABILITY OF THE DELL™ POWERCONNECT™ 6200 SERIES SWITCHES

WITH CISCO IOS AND CISCO CATOS-BASED SWITCHES

The MST Configuration Identifier consists of the following components:

•Configuration Identifier Format Selector – 1 byte value encoded as zero

•Configuration Name – 32 byte string

•Configuration Revision Level – 2 byte value

•Configuration Digest – 16 byte signature of type HMAC-MD5 created from the MST Configuration Table (a VID to MSTID mapping)

As there are multiple instances of Spanning Tree, there is an MSTP state maintained on a per-port, per-instance basis (or on a per-port, per-VLAN basis – as any VLAN can be in one and only one MSTI or CIST). For example, port A can be forwarding for instance 1 while discarding for instance 2.

The port states have changed since the publication of the IEEE 802.1d specification. The following table shows the port states for STP (802.1d) vs. MSTP (802.1s):

STP Port State	Admin Port State	MSTP Port State	Active Topology
(IEEE 802.1d)		(IEEE 802.1s)	(Port Role)
Disabled	Disabled	Discarding	Excluded (Disabled)
Disabled	Enabled	Discarding	Excluded (Disabled)
Blocking	Enabled	Discarding	Excluded (Alternate, Backup)
Listening	Enabled	Discarding	Included (Root, Designated)
Learning	Enabled	Learning	Included (Root, Designated)
Forwarding	Enabled	Forwarding	Included
			(Root, Designated, Master)

In order to support multiple spanning trees, an MSTP bridge must be configured with an unambiguous assignment of VIDs to spanning trees. This is achieved by:

1.Ensuring that the allocation of VIDs to filtering IDs (FIDs) is unambiguous.

The Dell PowerConnect 62xx series switch implements this with a fixed VID to FID assignment. Every VID is assigned to one and only one FID.

Figure 1: VID to FID Allocation

APRIL 2008 4