Specifications

8-148 set mstp Rapier Switch Software Reference
Software Release 2.7.3
C613-03098-00 REV A
set mstp
Syntax SET MSTp [CONFigname=name] [REVIsionlevel=level]
[MAXHOPS=1..40] [MAxage=6..40] [HEllotime=1..10]
[FOrwarddelay =4..30] [PROTocolversion ={STP|RSTP|
MSTP}] [STATicvlans={YES|NO|ON|OFF|TRUE|FALSE}]
where:
■ name is the MST configuration name. It is a string of up to 32 characters.
Valid characters are uppercase and lowercase letters, digits, and the
underscore. No other character types are allowed.
■ level is the MST configuration revision level, having the range 0-65535.
Description This command sets the MST configuration identifier values and the state
machine performance parameters. The configuration identifier contains:
■ the configuration name
■ the revision number
■ a digest of the VLAN to MSTI configuration table.
The state machine performance parameters are constants used by the CIST and
MSTI state machines.
When the MST algorithm calculates the active topology, it doesn’t consider the
VLAN membership of the ports. It doesn’t need to because IEEE 802.1Q-2003
assumes that the active topology will be determined first and that the VLANs
will be configured dynamically over the active topology, via GVRP. GVRP
configures the VLAN memberships of ports so that frames belonging to a
VLAN will be able to traverse the spanning tree (CIST or MSTI) that the VLAN
is assigned to.
When statically configured VLANs are used the process is reversed. The VLAN
memberships of ports are configured statically and then the active topology is
calculated. However, the MST algorithm does not consider the VLAN
memberships when calculating the active topology; it may choose a port that is
not a member of any of the VLANs assigned to the spanning tree to be the root
port, even though an alternate port that is a member of the VLANs may exist.
This would partition the network, preventing frames belonging to a VLAN
assigned to the spanning tree from traversing the network. In this situation it is
desirable that the algorithm considers the VLAN memberships of ports and
prevents partitioning where possible. It should choose the root port from the
ports that are members of the VLANs assigned to the spanning tree.
When using statically configured VLANs, each VLAN assigned to a given
spanning tree should have the same port membership; otherwise, partitioning
may occur.
The MST configuration identifier determines which MST region a switch
belongs to. The MST configuration identifier is conveyed in the MSTP BPDUs,
so the switch can check whether it is allocating VIDs to the same spanning tree
instance as a neighbouring switch. If the configuration identification of two
switches matches they are from the same MST region.
MSTP assigns the switch a default MST configuration identification consisting
of a unique default configuration name and a default revision level.