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MSTP, LACP (and possible UDLD?)

I'm setting up a new small backbone network (and edges too, partly) and I figured I'd do it _right_ this time and create a bit of redundancy and stuff. Anyway, I'm a bit confused right now...

But first - our setup:

Switch A - HP ProCurve 6200yl (K.12.57) Switch B - HP ProCurve 6200yl (K.12.57) Switch C - HP ProCurve 2900 (

Routing enabled in A and B. The 2900 in our main computer room.

The idea is to configure them in a triangle - with primary links between C-A (4x1000Mbps) and B-C (4x1000Mbps) with a backup link A-B (1x1000Mbps) in case something goes wrong and to use MSTP to make sure the A-B backup link normally is "cut".

The thing I'm a bit curious about is why STP only seems to block half (one direction) the A-B link (only one fiber link is used of the two we originally was thinking of using, the the second interface is administrative configured "down"):

Router A # show span Trk2 ... | Prio | Designated Hello Port Type | Cost rity State | Bridge Time PtP Edge ----- --------- + --------- ----- ---------- + ------------- ----- --- ---- Trk2 | 20000 16 Forwarding | 001c2e-149f40 2 Yes No

Router A # show int brief 3-4

Status and Counters - Port Status

| Intrusion MDI Flow Bcast Port Type | Alert Enabled Status Mode Mode Ctrl Limit ------- --------- + --------- ------- ------ ---------- ----- ----- ------ 1-Trk2 1000SX | No Yes Up 1000FDx off 0 2-Trk2 | No No Down off 0

Router B # show span Trk1 ... | Prio | Designated Hello Port Type | Cost rity State | Bridge Time PtP Edge ----- --------- + --------- ----- ---------- + ------------- ----- --- ---- Trk2 | 20000 16 Blocking | 001c2e-149f40 2 Yes No

Router B # show int brief 1-2

Status and Counters - Port Status

| Intrusion MDI Flow Bcast Port Type | Alert Enabled Status Mode Mode Ctrl Limit -------- --------- + --------- ------- ------ ---------- ----- ----- ------ 1-Trk2 1000SX | No Yes Up 1000FDx off 0 2-Trk2 1000SX | No No Down 1000FDx off 0

The trunks are configured as LACP trunks. After a little while we seem to have a nice broadcast storm circulating in this one-way regulated ethernet highway :-) (So we right now keep both the interface "down" manually to break this loop).

Relevant parts of the configuration from one of the routers/switches, A in this case - the others are configured similarly, in this one Trk1 is A-C and Trk2 is A-B (the backup link)):

trunk 1-2 Trk2 LACP trunk 3-6 Trk1 LACP spanning-tree spanning-tree Trk1 priority 0 spanning-tree Trk2 priority 1 spanning-tree config-name "IFM/Core" spanning-tree config-revision 1 spanning-tree priority 1

A related question - is is a good or a bad idea to enable "link-keepalive" (UDLD) on the links that make up these trunks?

- Peter

Reply to
Peter Eriksson
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This doesn't make sense. xSTP works on both directions of a link. If a port is blocked, it should be blocking both incoming and outgoing traffic, regardless of the version of STP (STP/RSTP/MSTP). It might be a bug, or it might be due to your configuration, but I don't see anything obvious that was explain this behavior.

You could try posting your query at:

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UDLD is typically used to detect "unidirectional links". If you think of the layered model, it runs below xSTP, so xSTP only considers a link up if UDLD reports that both directions are working fine. If your ports are directly connected and you are running LACP, I see marginal benefit in using this feature. It tends to be more useful if you have repeaters between the switches because then you have multiple hops between switches and a failure in one hop may not be seen by both switches, so having UDLD would help detect a problem immediately.

Anoop

Reply to
anoop

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