I came across a curly one like this a few months back - turned out the STP handling of native VLan frames VS a non-created but configured native vlan on the downstream switch port.
The downstream switchport was also configured for native vlan of 999 - BUT vlan999 was not created in the vlan database so defaulted to expecting STP frames untagged I think - it was something like that. -----Original Message----- From: cisco-nsp [mailto:[email protected]] On Behalf Of Patrick M. Hausen Sent: 15 October 2015 12:09 To: [email protected] Cc: [email protected] Subject: Re: [c-nsp] Spanning Tree works great - except when it doesn't Hello, first, thanks for all the questions. Precisely the kind of help I hoped for. While I'm really fluent with BGP and OSPF, I do not even know all the features you mention. STP has always "just worked" for us. OK, now for some more details ... > Am 15.10.2015 um 12:11 schrieb [email protected]: > > What protocol are you running? RPVST+ or MST? PVST spanning-tree mode pvst no spanning-tree optimize bpdu transmission spanning-tree extend system-id > What were the port roles when the loop formed? Sorry - what's a port role? > Did you have the default bridge priority on the new switch? Yes, and I can prove it ;-) VLAN0001 Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) VLAN0002 Bridge ID Priority 32770 (priority 32768 sys-id-ext 2) ... VLAN1001 Bridge ID Priority 33769 (priority 32768 sys-id-ext 1001) For all VLANs. > Is it possible that you had a unidirectional link? Possible, yes. I will check for that. Simply try to use the other trunk port only. - outside of business hours. > Copper or fibre for the trunk ports? Copper. > Any other STP features enabled? None that I know. > Root Guard? Loop Guard? BPDU filter? All at the IOS defaults. Whatever they may be. ;-) OK, what I know: no portfast or uplinkfast on the trunks, portfast only on the FE ports connected to servers. interface GigabitEthernet0/1 description Trunk zu Core 1 switchport trunk native vlan 999 switchport mode trunk ! interface GigabitEthernet0/2 description Trunk zu Core 2 switchport trunk native vlan 999 switchport mode trunk VLAN 999 is a dummy that has no active port or device anywhere, so one cannot accidentally inject traffic into VLAN 1 by connecting a server to a trunk port. > Did you verify the trunks were fully operational? Sort of. Trunks were up, VTP up and running, native VLAN identical on both ports on access switch and core - otherwise the trunk would not come up. Are there additional checks I can perform? > It won't be easy giving more advice until we can see the output from the > actual devices. Of course. I simply did not want to just dump the entire config into my first mail with all the probably irrelevant parts. I really appreciate your guidance, here. So, what "show xy" shall I use during the ~30 seconds I have when I'm at the data centre with both trunks plugged in - and come back with the output? > 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. LACP could work if the "core" switches are VSS ... which currently they are not. Possibly I read too much Greg Ferro, but I'm actually looking into TRILL and other Layer 2 multipathing protocols. The "problem" is that all products I can find are ten times as expensive as run-off-the-mill Cisco gear. 10k for a 48-port-1G access switch? *phew* ... If you wonder where I get these figures: http://pcmicrostore.com/arista-networks-7010t-48x-rj45-100-1000/cat-p/c/p7641704.html 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 _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
