System information

5-21
Multiple Instance Spanning-Tree Operation
802.1s Multiple Spanning Tree Protocol (MSTP)
Syntax: spanning-tree max-hops < hop-count >
This command resets the number of hops allowed for BPDUs
in an MST region. When an MSTP switch receives a BPDU, it
decrements the hop-count setting the BPDU carries. If the hop-
count reaches zero, the receiving switch drops the BPDU. Note
that the switch does not change the message-age and
maximum-age data carried in the BPDU as it moves through
the MST region and is propagated to other regions. (Range: 1
- 40; Default: 20)
Syntax: spanning-tree maximum-age <6 - 40 seconds>
Maximum age to allow for STP packets before discarding.
Default is 20 seconds.
Syntax: spanning-tree force-version < stp-compatible | rstp-operation | mstp-
operation >
Sets the spanning-tree compatibility mode. When the switch
is configured with MSTP mode, this command forces the
switch to emulate behavior of earlier versions of spanning tree
protocol or return to MSTP behavior. The command is useful
in test or debug applications, and removes the need to
reconfigure the switch for temporary changes in spanning-
tree operation.
stp-compatible: The switch applies 802.1D STP operation on all
ports.
rstp-operation: The switch applies 802.1w operation on all ports
except those ports where it detects a system using 802.1D
Spanning Tree.
mstp-operation: The switch applies 802.1s MSTP operation on
all ports where compatibility with 802.1D or 802.1w spanning
tree protocols is not required.
This command is available when the protocol version is set to
mstp (see 'protocol-version' later).
Note that even when mstp-operation is selected, if the switch
detects an 802.1D BPDU or an 802.1w BPDU on a port, it
communicates with the device linked to that port using STP
or RSTP BPDU packets. Also, if errors are encountered as
described in the “Note on MSTP Rapid State Transitions” on
page 17, setting force-version to stp-compatible forces the MSTP
switch to communicate out all ports using operations that are
compatible with IEEE 802.1D STP.