Spanning-tree ALTERNATE status blocking net mgt port

[Glen Van Lehn]

simple setup for a SAN: 2 HP3500's being setup as redundant pair for SAN project, currently empty and an HP5406 that is well connected on the data intranet. TRK1 & TRK2 on both 3500's are for the SAN vlan (which doesn't appear) on the 5406. Each 3500 has a single port config'd for the net mgt vlan, connected to the 5406, so we can access the 3500's.

I can get to one 3500 but not the other. When I look at spanning tree (serial port connection) on the inaccessible switch, I find that the net mgt link port is marked as ALTERNATE, and spanning tree is blocking it.

I was using a similar setup without a problem.
Software version on the 3500's is K.14.65, on the 5406 it is K.14.60.

I'm confused. Does anyone have an idea?

P.S. This thread has been moved from Switches, Hubs, Modems (Legacy ITRC forum) to ProCurve / ProVision-Based. - Hp Forum Moderator

[abdullah.shboull]

Kindly send a brief network diagram of your network

[Richard Brodie_1 · Accepted solution]

ALTERNATE means there is a shorter path to the root switch via another way. One possibility is that the other 3500 has been elected root. If so, I would want pick a switch that isn't in a test environment to be root.

However, your problem is that you have a ring, and RSTP is always going to break it at some point by taking one of the links down.

I think your confusion arises from thinking that you are running PVST, and if you don't have a loop in a particular VLAN, then it's OK. Sadly, that's not true with RSTP/MSTP.

There's a good introduction to MSTP here:
http://blog.ine.com/2010/02/22/understanding-mstp/

[Glen Van Lehn]

Richard, thanks for the link. It is very useful. ashboull, the diagrams at the beginning of the link map directly to my setup: SW1 & SW2 are the 3500's, SW3 is the 5406.

Topology 3 is the net-mgt setup. The SAN vlan is only between SW1 & SW2. but, yes the result is the triangle physical topology as shown. What still confuses me is that I've been running this setup for some months with three other switches.

Anyway, I'll work on the MSTP instances and report back.

[Glen Van Lehn]

Well, I decided to use BPDU-filter on the mgt vlan ports, because I really don't want to put _any_ data traffic onto the SAN fibers.

two other resources that may help others:

http://cdn.procurve.com/training/Manuals/ProCurve-and-Cisco-STP-Interoperability.pdf
(86 pg. config example !)

http://h40060.www4.hp.com/procurve/uk/en/pdfs/application-notes/How_to_improve_and_harden_spanning-tree_configuration_Configuration_note_Dec_08_A4.pdf
(I wanted a def of admin-edge vs auto-edge)