VTP Pruning vs Allowing VLANs on Trunk ports

[TOM FRANCHINA]

We would like to know best approach to reduce VLAN traffic on our network. We are currently trunking all fiber ports 802.1q.

We have about 73 VLANs across the network. We have done a lot of research and there seem to be a lot of theoretical answers but no one who uses it in practice.

Here is our current configs for fiber ports between closets:

Cisco WMH6509

interface GigabitEthernet2/8
 description Fiber To STB Lab 3850
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 no snmp trap link-status
end

Cisco STB Lab 3850

interface GigabitEthernet1/1/1
 description Fiber To WMH6509
 switchport mode trunk
end

We are considering:

VTP Pruning Enable

           or

 switchport
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 26,99,109,188
 switchport mode trunk

Thanks,

Tom

[paul driver · Accepted solution]

Hello

Manually pruning your vlan is my opinion the best option - It provide a total controllable approach to vtp pruning on the trunks

As for enabling vtp pruning dynamically it is the easiest option to deploy but I have found it not deterministic enough to trust which I have and found to my cost.

res

Paul

[TOM FRANCHINA]

Thanks Guys,

I work on a hospital network so I can't have any "surprises or quirks". I believe the allowed list is the safest and guaranteed to cut traffic based on your recommendations. It worked well in the test lab and was easy to see the results where prunning is much harder to evaluate. 

Thanks,

Tom

[Joseph W. Doherty]

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Posting

As I have some years (cough - decades) software development experience, I lean toward automation solutions, so, for example, I often prefer dynamic routing over static routing, and so likewise, I prefer VTP over manual configuration on multiple devices.

However, VTP does have some "quirks".  For example, this year I ran into an issue where an edge switch had a new VLAN defined to a port which wasn't in use on a transit switch, so VTP auto pruning, pruned it off the transit's uplink trunk.  (I was a bit of a pain to find the cause as VTP doesn't prune right away - edge worked for a bit and then it stopped working.  One fix would have been to stop using VTP auto-pruning, across the whole VTP domain, but instead, configured VTP to not auto-prune the needed VLAN across the needed trunk.)

So, as Paul notes, VTP auto pruning might be easier to get going, but be prepared for unexpected incidents (again, not saying you'll have any, just be prepared).  So, if you're prepared, I would go with VTP auto pruning, but if you want to "play safe", go with Paul's recommendation.