3Com WX3000 Configuring Guard Functions

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To do… Use the command… Remarks

Enter system view system-view —

Enter Ethernet port view interface interface-type interface-number —

Perform the mCheck operation stp mcheck Required

Configuration Example

# Perform the mCheck operation on GigabitEthernet 1/0/1.

1) Perform this configuration in system view

<device> system-view

[device] stp interface GigabitEthernet1/0/1 mcheck

2) Perform this configuration in Ethernet port view

<device> system-view

[device] interface GigabitEthernet1/0/1

[device-GigabitEthernet1/0/1] stp mcheck

Configuring Guard Functions

Introduction

The following guard functions are available on an MSTP-enabled device: BPDU guard, root guard, loop

guard, TC-BPDU attack guard, and BPDU drop.

Normally, the access ports of the devices operating on the access layer are directly connected to

terminals (such as PCs) or file servers. These ports are usually configured as edge ports to achieve

rapid transition. But they resume non-edge ports automatically upon receiving configuration BPDUs,

which causes spanning tree recalculation and network topology jitter.

Normally, no configuration BPDU will reach edge ports. But malicious users can attack a network by

sending configuration BPDUs deliberately to edge ports to cause network jitter. You can prevent this

type of attacks by utilizing the BPDU guard function. With this function enabled on a device, the device

shuts down the edge ports that receive configuration BPDUs and then reports these cases to the

administrator. Ports shut down in this way can only be restored by the administrator.

A root bridge and its secondary root bridges must reside in the same region. The root bridge of the CIST

and its secondary root bridges are usually located in the high-bandwidth core region. Configuration

errors or attacks may result in configuration BPDUs with their priorities higher than that of a root bridge,

which causes a new root bridge to be elected and network topology jitter to occur. In this case, flows that

should travel along high-speed links may be led to low-speed links, and network congestion may occur.

You can avoid this problem by utilizing the root guard function. Ports with this function enabled can only

be kept as designated ports in all spanning tree instances. When a port of this type receives

configuration BPDUs with higher priorities, it turns to the discarding state (rather than become a

non-designated port) and stops forwarding packets (as if it is disconnected from the link). It resumes the

normal state if it does not receive any configuration BPDUs with higher priorities for a specified period.