Page 436 7750 SR OS Services Guide
• The RSTP mode implements the improved convergence over shared media feature, for
example, RSTP will transition from discarding to forwarding in 4 seconds when operating
over shared media. The comp-dot1w mode does not implement this 802.1D-2004
improvement and transitions conform to 802.1w in 30 seconds (both modes implement
fast convergence over point-to-point links).
• In the RSTP mode, the transmitted BPDUs contain the port's designated priority vector
(DPV) (conforms to 802.1D-2004). Older implementations may be confused by the DPV
in a BPDU and may fail to recognize an agreement BPDU correctly. This would result in a
slow transition to a forwarding state (30 seconds). For this reason, in the comp-dot1w
mode, these BPDUs contain the port's port priority vector (conforms to 802.1w).
The 7750 SR supports two BDPU encapsulation formats, and can dynamically switch between
these (again on a per-SAP basis):
• IEEE 802.1D STP
• Cisco PVST
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