Solved: Hi,

jeff6strings · ‎02-09-2016

I found information and understand spanning tree path cost both the short and long method but I can't find how 40Gb links are valued if we use the long method. Currently in our Nexus infrastructure of N7K, N5K and N9K units with 10 and 40Gb links we are using the short method but before we change to long I would like to know how 40Gb links are valued.

Appreciate any help.
Jeff

Elliott Willink · ‎02-10-2016

Hi Jeff,

40gig links have a long value of 500

The info you are looking for is as follows:

"The recommended values for any intermediate link speed can be calculated as 20 000 000 000/(Link Speed in Kb/s)."

So in your case, 20,000,000,000 / 40,000,000 = 500

This comes from the enthralling document known as the "IEEE Standard for Local and metropolitan area networks— Common specifications Part 3: Media Access Control (MAC) Bridges— Amendment 2: Rapid Reconfiguration (2001)" Not sure if I can post links here, but do a google and you can track it down.

EDIT: what the hell, http://w3.tmit.bme.hu/courses/onlab/library/standards/802-1w-2001.pdf (Page 76, Note 3)

Hope this helps :)

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Kamran Mustafayev · ‎02-10-2016

Hi,

Bandwidth	Old STP value	New Long STP value
10 Mbps	100	2,000,000
100 Mbps	19	200,000
1 Gbps	4	20,000
N X 1 Gbps	3	10,000
10 Gbps	2	2,000
100 Gbps	N/A	200
1 Tbps	N/A	20
10 Tbps	N/A	2

Spanning Tree Path Cost with 40Gb