Spanning-Tree Operation

802.1D Spanning-Tree Protocol (STP)

Edge switches cannot be directly linked together using fast-uplink ports. For example, the connection between switches 4 and 5 in figure 5-14 is not allowed for fast-uplink operation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The ports

 

 

 

 

 

 

 

 

 

 

 

 

that make up

 

 

 

 

 

 

 

 

Switch 1

 

 

Switch 4

 

LAN

this link

 

 

 

 

 

 

(Root)

 

 

(5304-Edge)

 

 

 

 

 

 

cannot be

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

configured

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 3

 

 

 

 

 

as fast-

 

 

 

 

 

 

 

 

 

 

uplink ports.

 

 

 

 

 

 

 

 

 

 

Link blocked by STP:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 5

 

 

 

 

 

 

 

 

 

 

 

(5304-Edge)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5-14. Example of a Disallowed Connection Between Edge Switches

Apply fast-uplink only on the uplink ports of an edge switch. For example, on switch “4” (an edge switch) in figure 5-14 above, only the ports connecting switch “4” to switches “2” and “3” are upstream ports that would use fast uplink. Note also that fast uplink should not be configured on both ends of a point-to-point link, but only on the uplink port of an edge switch.

Ensure that the switch you intend as a backup root device will in fact become the root if the primary root fails, and that no ports on the backup root device are configured for fast-uplink operation. For example, if the STP Priority is the same on all switches—default: 32768—then the switch with the lowest MAC address will become the root switch. If that switch fails, then the switch with the next-lowest MAC address will become the root switch. Thus, you can use STP Priority to control which switch STP selects as the root switch and which switch will become the root if the first switch fails.

Fast-Uplink STP requires a minimum of two uplink ports.

Menu: Viewing and Configuring Fast-Uplink STP

You can use the menu to quickly display the entire STP configuration and to make any STP configuration changes.

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