Re: MSTP, LACP (and possible UDLD?)
- From: anoop <ghanwani@xxxxxxxxx>
- Date: Sat, 9 Feb 2008 07:47:28 -0800 (PST)
On Feb 8, 8:55 am, Peter Eriksson <pe...@xxxxxxxxxx> wrote:
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"):
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:
http://forums12.itrc.hp.com/service/forums/categoryhome.do?categoryId=269
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?
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
.
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- From: Peter Eriksson
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