Stp Pathcost-Standard; Stp Point-To-Point - 3Com 5500G-EI Command Reference Manual

RSTP Configuration Commands 335
You can configure no more than one primary root for a spanning tree but you can
configure one or more secondary roots for it. You cannot change the bridge
priority of a Switch if you configure it as a secondary root of a spanning tree.
Example
To designate the Switch as a secondary root of the STP, enter the following:
<SW5500>system-view
System View: return to User View with Ctrl+Z.
[SW5500]stp root secondary
stp root-protection Syntax
stp root-protection
undo stp root-protection
View
Ethernet Port View
Parameter
None
Description
Use the command to enable Root protection function on a
stp root-protection
Switch.
Use the command to restore the default status of
undo stp root-protection
Root protection function.
By default, root protection is not enabled.
Following incorrect configuration or malicious attack, a legal root of the network
may receive a BPDU with higher priority and lose its status as root, which causes
problems with the network topology. Such problems may pull the higher-speed
traffic to lower-speed links and cause network congestion.
To avoid this problem, RSTP provides Root protection function. After being
configured with Root protection, a port always stays as a designated port. Once
this port receives a BPDU with higher priority, it turns to listening status and will
not forward any packets (as if the link to it is disconnected). It will resume normal
status if it receives no BPDU with higher-priority for a period of time.
Example
To enable Root protection function on GigabitEthernet1/0/1 of the Switch, enter
the following:
<SW5500>system-view
System View: return to User View with Ctrl+Z.
[SW5500]interface GigabitEthernet1/0/1
[SW5500-GigabitEthernet1/0/1]stp root-protection