B5 & E1 STP Costs question

  • 0
  • 1
  • Question
  • Updated 2 years ago
  • Answered
I am new to my network and am documenting physical connections and STP paths and noticed that there are different costs between the B5 and E1 products.  I have some locations with mixed equipment and have noticed some odd paths due to the cost differences.

For instance my B5 which is one hop from the core and part of a ring of E1's has an alternate port blocking.

So I have an S4 -> B5 -> E1 ->E1 ->E1 ->E1 ->S4 
I would have expected the AP to be in the middle of the E1's not at the B5.

Hope that makes some sense. :)

How do you deal with the cost differences.  B5 says 20000, E1 say 1 for a fiber sfp links.

Any thoughts or help would be appreciated thanks!
Photo of Stephen McGuire

Stephen McGuire

  • 1,012 Points 1k badge 2x thumb
  • amused...

Posted 2 years ago

  • 0
  • 1
Photo of Erik Auerswald

Erik Auerswald, Embassador

  • 13,792 Points 10k badge 2x thumb
Hi Stephen,

you should be able to change the E1 to use the same STP port costs as the B5 with the
set spantree legacypathcost disable
command. The E1 uses the older numbers by default, the B5 uses the current values. You can check this setting with
show spantree legacypathcost
You can set the port cost individually, but I do not think that is a maintainable approach.
set spantree portcost PORTSTRING COST
Spanning tree needs to re-converge after this change, thus you should consider scheduling a maintenance window.

Photo of Stephen McGuire

Stephen McGuire

  • 1,012 Points 1k badge 2x thumb
Thanks!  As I was reading my first thought was will that cause a re-converge or not thanks for answering that. :)

I'll try to remember to post a follow up when I'm able to make the change.