MST max-hops number

[vlmacko]

Hello,

we have L2 switched network with MST enabled. Actual number of switches is 29. We plan add new switches into network. Default value of "spanning-tree mst max-hops" is 20, actual our value is 30.

I found in documentation maximum value for this parameter 40. Can anybody explain, why just this is maximum value for this parameter ?

Is it possible has more than 40 switches in L2 network, where MST is running ?

Can anybody help with any "design guide" of MST ?

Thanks a lot,

Vladimir

[jacquesd]

Hi Vladimir,

This has to do with the max-age of the BPDUs (20 by default). BPDUs are aged by 1 each time a switch forwards it. This means after 20 hops the BPDU will age and be discarded.

You should not worry about it if you do not have a 'chain' of 20 switches. For example, if you have a start configuration of 80 switches, the max hop would never exceed 1.

Thanks

Jacques

[vlmacko]

Problem is, that I have actualy 29 switches interconnected physicaly into 2 rings, and rings are interconnected as well. (actual value if max-hops is 30).

In some "bad" case I can get network into "chain".

Thanks a lot for help,

Vladimir