changing spanning-tree "cost" of ports ? - Do anyone know if this is a "hidden feature" ? :-)

[thomasthomsen]

I have a scenario where we have a new fiber-link between two switches that is also connected with a radio-link (the previous link).

We would of course like to utilize the fiber-link as primary, and only switch over to the radio-link in case of some fault on the fiberlink.

We could of course set the speed of the port that is connected to the radio-link to 100Mbit (to give it a higher cost), but we dont really like that solution because the radio-link is faster then 100Mbit (almost 1Gbit).

So do anyone know if there is a hidden "cost" setting I can put on switchports ? 🙂

Thanks

Thomas

[PhilipDAth]

No, but you could control this simply by selecting an appropriate port.

Port 1 has the highest default port cost, port 24 is lower, and port 48 is lowest.  Lets pretend you have a 24 port switch on each end.  If you plug your preferred circuit into port 24, and the backup into port 23, and both ports have the same speed configured, port 24 will win and port 23 will block.

And now you now why people often use the last ports on a switch as trunk links to other switches.

[RaphaelL]

I haven't messed with STP in a little while , but isn't the other way around ?

port 1 = 0x8001 ( 128.1 ) and port 24 = 0x8018 ( 128.24 ) 

Also the lowest portID starts from the lowest switch in a stack. It has nothing to do with the stacking order.  : https://community.meraki.com/t5/Switching/STP-Switch-Port-Identifier/m-p/148058

[PhilipDAth]

You might be right.  My recollection could be wrong.

@thomasthomsen do a test and see - but either way, you can control the backup port by using either a higher or lower port number.

[thomasthomsen]

Ill test it out and let you know, thanks so far.

Its been so long since I have really messed around with STP that even I didnt know (remember?) this about the ports.

[cmr · Accepted solution]

My money is on @RaphaelL here, sorry @PhilipDAth ...

 

Both are 10GbE links back to the core.

[PhilipDAth]

Even I am betting on @RaphaelL .