Service Manual

Version Description
8.4.2.1 Introduced the loopguard and rootguard options on the E-Series TeraScale,
C-Series, and S-Series.
8.3.7.0 Introduced on the S4810.
8.2.1.0 Introduced the hardware shutdown-on-violation option.
7.6.1.0 Introduced on the S-Series.
7.5.1.0 Introduced on the C-Series.
7.4.1.0 Added the optional Bridge Port Data Unit (BPDU) guard.
6.2.1.1 Introduced.
Usage Information
The BPDU guard option prevents the port from participating in an active STP topology in case a BPDU
appears on a port unintentionally, or is miscongured, or is subject to a DOS attack. This option places the
port into the Error Disable state if a BPDU appears, and a message is logged so that the administrator can
take corrective action.
NOTE: A port congured as an edge port, on a PVST switch, immediately transitions to the
forwarding state. Only ports connected to end-hosts should be congured as an edge port.
Consider an edge port similar to a port with a spanning-tree portfast enabled.
If you do not enable shutdown-on-violation, BPDUs are still sent to the route process module (RPM)
CPU.
You cannot enable root guard and loop guard at the same time on a port. For example, if you
congure loop guard on a port on which root guard is already congured, the following error
message is displayed: % Error: RootGuard is configured. Cannot configure
LoopGuard.
When used in a PVST+ network, loop guard is performed per-port or per-port channel at a VLAN level. If no
BPDUs are received on a VLAN interface, the port or port-channel transitions to a Loop-Inconsistent
(blocking) state only for this VLAN.
Enabling Portfast BPDU guard and loop guard at the same time on a port results in a port that remains in a
Blocking state and prevents trac from owing through it. For example, when Portfast BPDU guard and
loop guard are both congured:
• If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking
state and no trac is forwarded on the port.
• If no BPDU is received from a remote device, loop guard places the port in a Loop-Inconsistent Blocking
state and no trac is forwarded on the port.
Example
Dell(conf-if-gi-1/1)#spanning-tree pvst vlan 3 cost 18000
Dell(conf-if-gi-1/1)#end
Dell(conf-if-gi-1/1)#show config
!
interface GigabitEthernet 1/1
no ip address
switchport
spanning-tree pvst vlan 3 cost 18000
no shutdown
Dell(conf-if-gi-1/1)#end
Dell#
Per-VLAN Spanning Tree Plus (PVST+)
1145