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MSTP doesn't distribute VLANs?

Occasional Advisor

MSTP doesn't distribute VLANs?


I have a single 2824 with two switches hanging off it that also have a link between them.

I have enabled MSTP to protect 3 VLANs as per output below.

However what I really want to do is block VLANs 1&2 on link A, and block VLAN 3 on link B. Instead what it does it block them all on link A. I would have thought you could set a priority per port for each MST Instance so that it knows which port to defer to for each individual instance?

Have you seen this? Am I missing something?


switchA# sh span mst-config

MST Configuration Identifier Information

MST Configuration Name : Lab MSTP single
MST Configuration Revision : 1
MST Configuration Digest : 0xC01D53FBD2A3B9551DDB68FFF002D8FA

IST Mapped VLANs : 1

Instance ID Mapped VLANs
----------- ---------------------------------------------------------
1 2
2 3

switchA# sh span instance 1

MST Instance Information

Instance ID : 1
Mapped VLANs : 2

Switch Priority : 32768

Topology Change Count : 1
Time Since Last Change : 107 mins

Regional Root MAC Address : 0016b9-0b0be0
Regional Root Priority : 32768
Regional Root Path Cost : 0
Regional Root Port : This switch is root
Remaining Hops : 20
Port Type Cost Priority Role State Bridge
----- --------- --------- -------- ---------- ---------- -------------
1 100/1000T Auto 128 Disabled Disabled

Trk1 20000 128 Designated Forwarding 0016b9-0b0be0
Trk2 20000 128 Backup Blocking 0016b9-0b0be0

Occasional Advisor

Re: MSTP doesn't distribute VLANs?

Oh right I think I've got it - misread a bit of the manual. Priority 8 is the default, so I set the ones I want to have priority to 7, something like:

span instance 1 Trk1 priority 7
span instance 2 Trk2 priority 7

This the way for instances, but for the IST I'm not sure how you set a priority. Is it just a normal port priority? Not too worried about that though.
Occasional Advisor

Re: MSTP doesn't distribute VLANs?

So I guess the next question is:

- can you set TX/RX priorities? So one trunk takes all TX for VLAN 2 say, and the other trunk takes all RX for VLAN 2?