Enhancements in Release F.02.11

Fast-Uplink Spanning Tree Protocol (STP)

Operating Rules for Fast Uplink

■A switch with ports configured for fast uplink must be an edge switch and not either an interior switch or the STP root switch.

Configure fast-uplink on only the edge switch ports used for providing redundant STP uplink connections in a network. (Configuring Fast-Uplink STP on ports in interior switches can create network performance problems.) That is, a port configured for STP uplink should not be connected to a switch that is sequentially further away from the STP root device. For example, switch "4" in figure 68 (page 150) is an edge switch.

■Configure fast uplink on a group (two or more) of redundant edge-switch uplink ports where only one port in the group is expected to be in the forwarding state at any given time.

■Edge switches cannot be directly linked together using fast-uplink ports. For example, the connection between switches 4 and 5 in figure 69 is not allowed for fast-uplink operation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The ports that

 

 

 

 

 

 

 

 

 

 

 

 

 

make up this

 

 

 

 

 

 

 

 

Switch 1

 

 

 

Switch 4

 

 

LAN

link cannot be

 

 

 

 

 

 

(Root)

 

 

configured as

 

(2512-Edge)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

fast-uplink

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 3

 

 

 

 

 

 

ports.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Link blocked by STP:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch 5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(2524-Edge)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 69. 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 69 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.

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