[Rstplib-users] Re: operEdge: per Port or per MSTi in 802.1s ?

[Tony J. <to...@je...>]

The use of operEdge to signal an edge port allows the Spanning Tree state 
machines to make optimizations in transitions to Forwarding on such ports, 
based on the assumption that because the port is an edge port, there 
is   no bridge attached to the port (which, by definition, would mean that 
the port is not an edge port).

Seeing *any* BPDU on a port that had been flagged as an edge port means 
that there is a bridge out there - and therefore, that the port is not at 
the edge of the bridged LAN, and therefore, any spanning tree optimizations 
that were based on the assumption that the port was an edge port are no 
longer valid.  Continuing to behave as an edge port in these circumstances 
would carry the risk of creating loops in one or more of the MSTIs and/or 
CIST. Hence, it is only necessary to have a single instance of the variable 
per port for it to do its job.

Regards,
Tony

At 12:10 13/12/2001 +0200, Alex Ruzin wrote:

>Hi,
>
>In 13.25 of 802.1s it is pointed, that the variable operEdge is  "single
>per-Port instance
>applies to the CIST and to all MSTIs."
>
>Why ?
>If a Port had received BPDU with tag of some MSTi and had
>not received any BPDU from another,
>why we have to consider it as operEdge port in this second MSTi ?
>
>Best regards, Alex
>---------------------
>Open Source RSTP  https://sourceforge.net/projects/rstplib/
>Optical Access Ltd. http://www.opticalaccess.com