Spanning-Tree Operation

802.1D Spanning-Tree Protocol (STP)

In figure 5-20:

Port A1 and Trk1 (trunk 1; formed from ports 2 and 3) are redundant fast-uplink STP links, with trunk 1 forwarding (the active link) and port A1 blocking (the backup link). (To view the configuration for port A1 and Trk1, see figure 5-18 on page 5-39.)

If the link provided by trunk 1 fails (on both ports), then port A1 begins forwarding in fast-uplink STP mode.

Ports A5, A6, and A24 are connected to end nodes and do not form redundant links.

CLI: Viewing and Configuring Fast-Uplink STP

Using the CLI to View Fast-Uplink STP. You can view fast-uplink STP using the same show commands that you would use for standard STP opera­ tion:

Syntax: show spanning-tree

Lists STP status.

Syntax: show spanning-tree config

Lists STP configuration for the switch and for individual ports.

For example, figures 5-21 and 5-22 illustrate a possible topology, STP status listing, and STP configuration for a switch with:

STP enabled and the switch operating as an Edge switch

Port A1 and trunk 1 (Trk1) configured for fast-uplink STP operation

Several other ports connected to PC or workstation end nodes

 

 

STP

 

 

 

 

 

 

2610, 2610

 

Block

 

Interior

 

STP

 

 

 

 

 

PWR

 

 

 

 

Switch

 

Root

 

 

 

 

 

 

 

 

 

 

 

 

 

with STP

 

Device

 

 

switch

 

 

 

 

 

 

LAN

 

 

 

 

Enabled

 

 

 

Operating

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

as an Edge

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Port

Trunk

Figure 5-21. Example Topology for the Listing Shown in Figure 5-22

5-41