Virtual Private LAN Services
7750 SR OS Services Guide Page 519
Configuring STP Bridge Parameters in a VPLS
Modifying some of the Spanning Tree Protocol parameters allows the operator to balance STP
between resiliency and speed of convergence extremes. Modifying particular parameters,
mentioned below, must be done in the constraints of the following two formulae:
2 x (Bridge_Forward_Delay - 1.0 seconds) >= Bridge_Max_Age
Bridge_Max_Age >= 2 x (Bridge_Hello0_Time + 1.0 seconds)
The following STP parameters can be modified at VPLS level:
• Bridge STP Admin State on page 519
• Mode on page 520
• Bridge Priority on page 520
• Max Age on page 521
• Forward Delay on page 521
• Hello Time on page 522
• MST Instances on page 523
• MST Max Hops on page 523
• MST Name on page 523
• MST Revision on page 523
STP always uses the locally configured values for the first three parameters (Admin State, Mode
and Priority).
For the parameters Max Age, Forward Delay, Hello Time and Hold Count, the locally configured
values are only used when this bridge has been elected root bridge in the STP domain, otherwise
the values received from the root bridge are used. The exception to this rule is: when STP is
running in RSTP mode, the Hello Time is always taken from the locally configured parameter.
The other parameters are only used when running mode MSTP.
Bridge STP Admin State
The administrative state of STP at the VPLS level is controlled by the shutdown command.
When STP on the VPLS is administratively disabled, any BPDUs are forwarded transparently
through the 7750 SR. When STP on the VPLS is administratively enabled, but the administrative
state of a SAP or spoke SDP is down, BPDUs received on such a SAP or spoke SDP are
discarded.
CLI Syntax: config>service>vpls service-id# stp
no shutdown
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