Interoperability With Ieee 802.1D-1998 Stp; Configuring Stp - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Chapter 17 Configuring STP and MST
Figure 17-12
Switch

Interoperability with IEEE 802.1D-1998 STP

A switch running MST supports a built-in protocol migration feature that enables it to interoperate with
802.1D switches. If this switch receives an 802.1D configuration BPDU (a BPDU with the protocol
version set to 0), it sends only 802.1D BPDUs on that port. An MST switch also can detect that a port is
at the boundary of a region when it receives an 802.1D BPDU, an MST BPDU (Version 3) associated
with a different region, or an RSTP BPDU (Version 2).
However, the switch does not automatically revert to the MST mode if it no longer receives 802.1D
BPDUs because it cannot detect whether the 802.1D switch has been removed from the link unless the
802.1D switch is the designated switch. A switch might also continue to assign a boundary role to a port
when the switch to which this switch is connected has joined the region. To restart the protocol migration
process (force the renegotiation with neighboring switches), use the clear spanning-tree
detected-protocols privileged EXEC command.
If all the 802.1D switches on the link are RSTP switches, they can process MST BPDUs as if they are
RSTP BPDUs. Therefore, MST switches send either a Version 0 configuration and topology change
notification (TCN) BPDUs or Version 3 MST BPDUs on a boundary port. A boundary port connects to
a LAN, the designated switch of which is either a single spanning tree switch or a switch with a different
MST configuration.

Configuring STP

These sections describe how to configure STP on VLANs:
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OL-11439-03
Detecting Unidirectional Link Failure
Superior
BPDU
A
Inferior BPDU,
Designated + Learning bit set
Default STP Configuration, page 17-26
Enabling STP, page 17-26
Enabling the Extended System ID, page 17-28
Configuring the Root Bridge, page 17-28
Configuring a Secondary Root Bridge, page 17-29
Configuring STP Port Priority, page 17-30
Configuring STP Port Cost, page 17-32
Configuring the Bridge Priority of a VLAN, page 17-33
Configuring the Hello Time, page 17-34
Configuring the Forward-Delay Time for a VLAN, page 17-35
Configuring the Maximum Aging Time for a VLAN, page 17-35
Enabling Rapid-PVST, page 17-36
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Switch
B
Configuring STP
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