2015-10-15 11:37 skrev Patrick M. Hausen:
Hi, all,
we still rely on STP in our data centre. Top-of-rack switches are
connected
to two core switches with Gigabit configured as trunks.
The two core switches have
spanning-tree vlan 1-1005 priority 24576
and
spanning-tree vlan 1-1005 priority 28672
respectively, to make sure the first one is the root with the second
as a backup.
Recently I replaced top-of-rack switch. Switched a WS-C2950T-24 for a
WS-C2960-48TT-L. We have quite a few of those in operation, already
buying them refurbished in the last couple of months.
To my big surprise the new switch that I preconfigured and booted for
minimal
downtime, then just moved the cables, put both uplink/trunk ports into
the
forwarding state and quickly flooded the console with:
00:26:02: %SW_MATM-4-MACFLAP_NOTIF: Host 001e.f7f6.8f80 in vlan 1 is
flapping between port Gi0/2 and port Gi0/1
00:26:03: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 1 is
flapping between port Gi0/1 and port Gi0/2
...
What the ...? For the moment I could only solve the problem by
unplugging one of
the trunks. I'm not quite sure if I really built a loop that would
have brought my entire
network down, but definitely all servers on that particular switch
were unreachable
- the switch was flooded and completely overloaded.
The software on the new switch is
Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version
15.0(2)SE5, RELEASE SOFTWARE (fc1)
How can I debug this? I have remote access to the misbehaving switch
and the old
one it replaced is on my desk. Of course I can provide configuration
details, if needed.
Activating the second uplink port is only possible for short periods
of time, so I'd
like to prepare as well as possible ;-)
Thanks for any hints.
Second with all the fun we have with STP and VTP: we are actively
looking into products
that can replace our layer 2/STP architecture. As far as I know there
are products that can
scale in a mesh and use all active links for traffic.
But when I lookup, say, Brocade's line of switches, we are faced with
price tags ... well.
The 48-Port FE switches cost about a thousand when they were current
hardware and
we bought new. One switch supports 16 servers in our rack. Now we get
them for 350
refurbished.
Of course I would happily pay a thousand or two/three for a more
modern architecture
plus GE/10G-uplink instead of FE/GE-uplink. But all products I find
seem to be in the
10k and more range. Which unfortunately is completely out of reach for
an access switch
for us.
Any suggestions on what I should look for?
Kind regards
Patrick
--
punkt.de GmbH * Kaiserallee 13a * 76133 Karlsruhe
Tel. 0721 9109 0 * Fax 0721 9109 100
[email protected] http://www.punkt.de
Gf: Jürgen Egeling AG Mannheim 108285
What protocol are you running? RPVST+ or MST? What were the port roles
when the loop formed? Did you have the default bridge priority on the
new switch? Is it possible that you had a unidirectional link? Copper or
fibre for the trunk ports? Any other STP features enabled? Root Guard?
Loop Guard? BPDU filter? Did you verify the trunks were fully
operational?
It won't be easy giving more advice until we can see the output from the
actual devices.
For your second question, there are lots of different options such as
stacking, VSS, VPC which can be used for less painful STP
implementations. Nothing is perfect though and you need to understand
why you choose a certain architecture. Then you also have FabricPath or
TRILL to build L2 network not relying on STP.
Regards,
Daniel Dib
Senior Network Architect
CCIE #37149
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