3com S7906E Manuel De Montage

 

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When receiving topology change (TC) BPDUs (the BPDUs used to notify topology changes), a switch 
flushes its forwarding address entries. If someone forges TC-BPDUs to attack the switch, the switch will 
receive a large number of TC-BPDUs within a short time and be busy with forwarding address entry 
flushing. This affects network stability. 

With the TC-BPDU guard function, you can set the maximum number of immediate forwarding address 
entry flushes that the switch can perform within a certain period of time after receiving the first TC-BPDU. 
For TC-BPDUs received in excess of the limit, the switch performs forwarding address entry flush only 
when the time period expires. This prevents frequent flushing of forwarding address entries. 

Follow these steps to enable TC-BPDU guard: 

Enter system view 

 

— 

Enable the TC-BPDU guard 
function  

 

Optional 
Enabled by default 

Configure the maximum 
number of forwarding address 
entry flushes that the device 
can perform within a specific 
time period after it receives the 
first TC-BPDU 

stp tc-protection threshold 
number 

Optional 
6 by default 

 

We recommend that you keep this feature enabled. 

 

An S7900E switch installed with an OLT card can work as an EPON OLT. In this case, you can remotely 
configure MSTP for an ONU attached to the OLT in ONU port view, as shown in the table below.  

Note that: 

z

 

An ONU port supports STP/RSTP/MSTP. However, an ONU port supports only MSTI 0 among all 
MSTIs.  

z

 

The STP priority of an ONU port is fixed to 0. To ensure the network operates normally, do not 
configure the ONU as the STP root bridge.