HP ProCurve Series 3400cl Release Notes page 127

[root-guard]
MSTP only. When a port is enabled as root-guard, it cannot be selected as the root
port even if it receives superior STP BPDUs. The port is assigned an "alternate"
port role and enters a blocking state if it receives superior STP BPDUs. The
BPDUs received on a root-guard port are ignored. All other BPDUs are accepted
and the external devices may belong to the spanning tree as long as they do not
claim to be the Root device. (Default: No - disabled)
Note: In standard Spanning Tree Protocol operation, the calculation of active
network topologies may be an issue when switches outside the core region of a
network are under shared or limited administrative control. Such a switch may
become a Root Bridge for the entire network and create non-optimal forwarding
paths. By enabling the root-guard feature on ports that face outside the core
network, external boundaries for the core network are created to ensure the Root
Bridge is located within the core network.
[tcn-guard]
When tcn-guard is enabled for a port, it causes the port to stop propagating
received topology change notifications and topology changes to other ports.
(Default: No - disabled)
Syntax: spanning-tree < port-list > < hello-time | path-cost | point-to-point-mac | priority >
[ hello-time < global | 1 - 10 >
When the switch is the CIST root, this parameter specifies the interval (in
seconds) between periodic BPDU transmissions by the designated ports. This
interval also applies to all ports in all switches downstream from each port in
the < port-list >. A setting of global indicates that the ports in < port-list > on the
CIST root are using the value set by the global spanning-tree hello-time value.
When a given switch "X" is not the CIST root, the per-port hello-time for all active
ports on switch "X" is propagated from the CIST root, and is the same as the
hello-time in use on the CIST root port in the currently active path from switch
"X" to the CIST root. (That is, when switch "X" is not the CIST root, then the
upstream CIST root's port hello-time setting overrides the hello-time setting
configured on switch "X". (Default Per-Port setting: Use Global. Default Global
Hello-Time: 2.)
[ path-cost < auto | 1..200000000 > ]
Assigns an individual port cost that the switch uses to determine which ports
are forwarding ports in a given spanning tree. In the default configuration
(auto) the switch determines a port's path cost by the port's type:
– 10 Mbps: 2000000
– 100 Mbps: 200000
– 1 Gbps: 20000
Enhancements
Release M.10.37 Enhancements
117