Specifications
Switching 8-43
Software Release 2.7.3
C613-03098-00 REV A
CIST Regional Root
Identifier
18–25 ID of the current CIST regional root bridge.
CIST Port Identifier 26–27 CIST port identifier of the transmitting bridge port.
Message Age 28–29 Message age timer value.
Max Age 30–31 Timeout value to be used by all bridges in the bridged
network. This value is set by the root. Some implementations
of MSTP may choose not to use this value.
Hello Time 32–33 Time interval between the generation of configuration
BPDUs by the root bridge.
Forward Delay 34–35 A timeout value used to ensure forward delay timer
consistency when transferring a port to the forwarding
state. It is also used for ageing filtering database dynamic
entries following changes in the active topology.
Version 1 Length 36 Used to convey the Version 1 length. It is always transmitted
as 0.
Version 3 Length 37–38 Used to convey the Version 3 length. It is the number of
octets taken by the parameters that follow in the BPDU.
MST Configuration
Identifier
39–89 An identifier comprising elements of the following:
Format Selector
Configuration Name
Revision Level
Configuration Digest.
CIST Internal Root
Path Cost
90–93 Path cost to the CIST regional root.
CIST Bridge
Identifier
94–101 CIST bridge identifier of the transmitting bridge.
CIST Remaining
Hops
102 Remaining hops which limits the propagation and longevity
of received spanning tree information for the CIST.
MSTI Configuration
Messages
(may be absent)
103–39
plus
Version
3 Length
See Table 8-14 on page 8-43.
Table 8-14: MSTI configuration messages
Field Name Octets Description
MSTI Flags 1 Bits 1 through 8, convey the topology change flag, proposal
flag, port role (two bits), Learning flag, forwarding flag,
agreement flag, and master flag for this MSTI.
MSTI Regional Root
Identifier
2–9 This includes the value of the MSTID for this configuration
message encoded in bits 4 through 1 of octet 1, and bits 8
through 1 of octet 2.
MSTI Internal Root
Path Cost
10-13 Internal Root Path Cost.
MSTI Bridge Priority 14 Bits 5 through 8 convey the value of the bridge identifier
priority for this MSTI. Bits 1 through 4 of Octet 14 are
transmitted as 0, and ignored on receipt.
Table 8-13: MST Bridge Protocol Data Units (BPDUs) (Continued)