System information

9-110
Configuring Advanced Features
Spanning Tree Protocol (STP)
Configuring Advanced
Features
Caution The Fast Mode configuration should be used only on switch ports connected
to end nodes. Changing the Mode to Fast on ports connected to hubs, switches,
or routers may cause loops in your network that STP may not be able to
immediately detect, in all cases. This will cause temporary loops in your
network. After the fast start-up sequence, though, the switch ports operate
according to the STP standard, and will adjust their state to eliminate continu-
ing network loops.
To Configure Fast Mode for a Switch Port:
■ In the CLI, use this command: spanning tree mode <port list> fast
For example, to configure Fast mode for ports 1-3 and 5:
HP2512(config)# spanning-tree ethernet 1-3,5 mode fast
■ In the menu interface, go to the Main Menu and follow the steps under
“Menu: Configuring STP” on page 9-103.
STP Operation with 802.1Q VLANs
As recommended in the IEEE 802.1Q VLAN standard, when spanning tree is
enabled on the switch, a single spanning tree is configured for all ports across
the switch, including those in separate VLANs. This means that if redundant
physical links exist in separate VLANs, spanning tree will block all but one of
those links. However, if you need to use STP on the Switch 2512 or Switch
2524 in a VLAN environment with redundant physical links, you can prevent
blocked redundant links by using a port trunk. The following example shows
how you can use a port trunk with 802.1Q (tagged) VLANs and STP without
unnecessarily blocking any links or losing any bandwidth.