Users Guide

Parameters
stp-id Enter the STP instance ID. The range is 0.
cost cost Enter the keyword cost followed by a number as the cost. The range is 1 to
65535. The defaults are:
● 100 Mb/s Ethernet interface = 19.
● 1-Gigabit Ethernet interface = 4.
● 10-Gigabit Ethernet interface = 2.
● Port Channel interface with 100 Mb/s Ethernet = 18.
● Port Channel interface with 1-Gigabit Ethernet = 3.
● Port Channel interface with 10-Gigabit Ethernet = 1.
loopguard (C-, S-, and E-Series TeraScale and S4810 only) Enter the keyword loopguard to
enable STP loop guard on a port or port-channel interface.
rootguard (C-, S-, and E-Series TeraScale and S4810 only) Enter the keyword rootguard to
enable STP root guard on a port or port-channel interface.
portfast
[bpduguard
[shutdown-on-
viol ation]]
Enter the keyword portfast to enable Portfast to move the interface into
Forwarding mode immediately after the root fails.
Enter the optional keyword bpduguard to disable the port when it receives a
BPDU.
Enter the optional keyword shutdown-on-violation to hardware disable an
interface when a BPDU is received and the port is disabled.
priority priority Enter keyword priority followed by a number as the priority. The range is zero
(0) to 15. The default is 8.
Defaults cost = depends on the interface type; priority = 8
Command Modes INTERFACE
Command
History
Version 8.3.10.1 Introduced the loopguard and rootguard options on the S4810.
Version 8.4.2.1 Introduced the loopguard and rootguard options on the E-Series TeraScale,
C-Series, and S-Series.
Version 8.3.7.0 Introduced on the S4810.
Version 8.2.1.0 Introduced the shutdown-on-violation option.
Version 7.7.1.0 Introduced on the S-Series.
Version 7.5.1.0 Introduced on the C-Series.
Version 6.2.1.1 Introduced on the E-Series.
Usage
Information
If you enable portfast bpduguard on an interface and the interface receives a BPDU, the software
disables the interface and sends a message stating that fact. The port is in ERR_DISABLE mode, yet
appears in the show interface commands as enabled. If you do not enable shutdown-on-
violation, BPDUs still are sent to the RPM CPU.
STP loop guard and root guard are supported on a port or port-channel enabled in any Spanning Tree
mode: Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP), Multiple Spanning Tree
Protocol (MSTP), and Per-VLAN Spanning Tree Plus (PVST+).
Root guard is supported on any STP-enabled port or port-channel except when used as a stacking port.
When enabled on a port, root guard applies to all VLANs configured on the port.
STP root guard and loop guard cannot be enabled at the same time on a port. For example, if you
configure loop guard on a port on which root guard is already configured, the following error message is
displayed: % Error: RootGuard is configured. Cannot configure LoopGuard.
Do not enable Portfast BPDU guard and loop guard at the same time on a port. Enabling both features
may result in a port that remains in a blocking state and prevents traffic from flowing through it. For
example, when Portfast BPDU guard and loop guard are both configured:
1558 Spanning Tree Protocol (STP)