Bridge Protocol Data Unit Format And Processing - Cisco ONS 15454 Software Feature And Configuration Manual
Sonet / sdh ml-series multilayer ethernet card
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Chapter 6
Configuring STP and RSTP
Figure 6-5
8. Agreement
Bridge Protocol Data Unit Format and Processing
The RSTP BPDU format is the same as the IEEE 802.1D BPDU format except that the protocol version
is set to 2. A new Length field is set to zero, which means that no version 1 protocol information is
present.
Table 6-4
Bit
0
1
2–3:
4
5
6
7
The sending switch sets the proposal flag in the RSTP BPDU to propose itself as the designated switch
on that LAN. The port role in the proposal message is always set to the designated port.
The sending switch sets the agreement flag in the RSTP BPDU to accept the previous proposal. The port
role in the agreement message is always set to the root port.
Cisco ONS 15454 SONET/SDH ML-Series Multilayer Ethernet Card Software Feature and Configuration Guide, R4.0
January 2004
Sequence of Events During Rapid Convergence
4. Agreement
5. Forward
2. Block
9. Forward
6. Proposal
Table 6-4
shows the RSTP flag fields.
RSTP BPDU Flags
Function
Topology change (TC)
Proposal
Port role:
00
Unknown
01
Alternate port
10
Root port
11
Designated port
Learning
Forwarding
Agreement
Topology change acknowledgement
1. Proposal
Edge port
3. Block
11. Forward
7. Proposal
Root port
Designated port
Bridge Protocol Data Unit Format and Processing
10. Agreement
6-13
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