Spanning tree question

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Cas
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Posts: 3
Joined: 16 May 2017 07:01

Spanning tree question

Post by Cas » 16 May 2017 07:17

Hi,

I am a Cisco / Juniper guy temporarily hired out to an organisation where Alcatel is the main platform. I noticed that after cleaning up a massive load of issues in OmniVista and fixing a lot of snmp user errors there is an issue with spanning tree.
That is to say, spanning tree does not seem to be configured.

I have a 6900-X40 as a core switch with a number of 6450-P48, 6450-P10 and 6450-C10 attached as access switches.

My plan is to do the following:
add

Code: Select all

 spantree vlan <n> priority 4096
to the core ( where n is any configured vlan )

add

Code: Select all

 spantree vlan <n> priority 8192
to the core at the core switch at the (layer 2 connected ) backup site

Questions are :
Is the the way to go about is ?
Will it disrupt production ?

I know this can be fixed with LAGS but there is no possibility to do this in the time frame i have left. Help is greatly appreciated.

Thanks...

devnull
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Location: Germany

Re: Spanning tree question

Post by devnull » 17 May 2017 02:18

If you have a pair of 6900 - VC and LAG is the way to go.
Spanning tree should be enabled by default on AOS, if it is in Alcatel 1x1 (similar to rapid-pvst+) which is default your commands should be the way to change the priority for the named vlan.

Hence configuring it with 4096 on all vlans on primary Switch will make this switch Rootbridge for all configured VLANs, and configuring 8192 on the backup will make that backup root.

Will it disrupt ? Yes, probably. Fiddeling with prioritys will cause a new root bridge to be elected hence several ports will go into discarding/learning before the reconverge -> expect a couple of seconds "hicups" while changing, but it should not be down for a longer time.

Cas
Member
Posts: 3
Joined: 16 May 2017 07:01

Re: Spanning tree question

Post by Cas » 23 May 2017 09:52

Thanks devnull I appreciate your help...

The design document shows :

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spantree pvst+compatibility enable
spantree vlan 9 admin-state enable
not much more. To me it looks like an unfinished config, or one designed by someone not knowlegeable in the field of Spanning tree..

We do see unwanted rootbridge elections after switch reboots and I would like to prevent that. We're scheduling a change and I'll see if I can post he results.

Cas
Member
Posts: 3
Joined: 16 May 2017 07:01

Re: Spanning tree question

Post by Cas » 04 Jul 2017 05:44

So the proposed change has been implemented and OMniVista has become more quiet.

What I do see is some spantree root changes from branch locations. Those switches are OS6540 models and I can find nothing spanning tree like in the commandline. Only something called loopback-detection.

Is it at all possible to set a rootbridge priority on OS6450 models ?

Thanks...

silvio
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Re: Spanning tree question

Post by silvio » 05 Jul 2017 14:56

Hi,
normaly at the access switches you don't need anything to configure. Prio ist per default at all switches 0x8000 and mode 1x1 (per vlan). Only at the core you need to configure the prio to f.e 0x1000 (= 4096) at all vlans. And mode need also to be perVlan. change spantree traps can be caused by disconnecting/connecting one switche in the network. look in the switches per vlan for the count of topology changes and the last change. Use the command show spantree 10 and show spantree vlan 10 (R6/R8).
For more security you can use userports with bpdu shutdown to disable ports with unwanted stp packets. Also you can use lpd (loopback-detection) for it.
Both functions at the edge-ports of the access switches.
regards
Silvio

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