Cisco WS-C2960-24TC-S Software Guide - Page 349
Designating the Neighbor Type, Restarting the Protocol Migration Process
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Chapter 16 Configuring MSTP Configuring MSTP Features Designating the Neighbor Type A topology could contain both prestandard and IEEE 802.1s standard compliant devices. By default, ports can automatically detect prestandard devices, but they can still receive both standard and prestandard BPDUs. When there is a mismatch between a device and its neighbor, only the CIST runs on the interface. You can choose to set a port to send only prestandard BPDUs. The prestandard flag appears in all the show commands, even if the port is in STP compatibility mode. Beginning in privileged EXEC mode, follow these steps to override the default link-type setting. This procedure is optional. Step 1 Step 2 Command configure terminal interface interface-id Step 3 Step 4 Step 5 Step 6 spanning-tree mst pre-standard end show spanning-tree mst interface interface-id copy running-config startup-config Purpose Enter global configuration mode. Specify an interface to configure, and enter interface configuration mode. Valid interfaces include physical ports. Specify that the port can send only prestandard BPDUs. Return to privileged EXEC mode. Verify your entries. (Optional) Save your entries in the configuration file. To return the port to its default setting, use the no spanning-tree mst prestandard interface configuration command. Restarting the Protocol Migration Process A switch running MSTP supports a built-in protocol migration mechanism that enables it to interoperate with legacy IEEE 802.1D switches. If this switch receives a legacy IEEE 802.1D configuration BPDU (a BPDU with the protocol version set to 0), it sends only IEEE 802.1D BPDUs on that port. An MSTP switch also can detect that a port is at the boundary of a region when it receives a legacy BPDU, an MST BPDU (Version 3) associated with a different region, or an RST BPDU (Version 2). However, the switch does not automatically revert to the MSTP mode if it no longer receives IEEE 802.1D BPDUs because it cannot detect whether the legacy switch has been removed from the link unless the legacy switch is the designated switch. A switch also might continue to assign a boundary role to a port when the switch to which it is connected has joined the region. To restart the protocol migration process (force the renegotiation with neighboring switches) on the switch, use the clear spanning-tree detected-protocols privileged EXEC command. To restart the protocol migration process on a specific interface, use the clear spanning-tree detected-protocols interface interface-id privileged EXEC command. OL-8603-04 Catalyst 2960 Switch Software Configuration Guide 16-25
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