Bridge Protocol Data Unit Format And Processing - Cisco ONS 15454 Software Feature And Configuration Manual

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