switchport trunk allowed vlan?

[Anthony Walters]

Adding a vlan 820 to existing port channel trunk which currently allows many vlans.

Question is:

What is the best way to add vlan820 with least impact to network. Portchannels from 6513 core with IOS to Nexus 5k

(Already have a change window)

Copy existing vlans, add 820 and paste under:

switchport trunk allowed vlan 1,2,5,12,20,820

Or

switchport trunk allowed vlan Add vlan820

Thanks

[Richard Burts · Accepted solution]

Anthony

The second choice (switchport trunk allowed vlan add is the better and less disruptive alternative. I have done this often and it works with no impact to the network.

HTH

Rick

[Anthony Walters]

Thank you. I will use that command.

[jimmysands73_2]

Juuuuuuuust curious....

If those vlans are already allowed on the trunk

switchport trunk allowed vlan 1,2,5,12,20,820

How could adding another vlan disrupt the network?  Does it reset the interface?   Tried to test locally but seeing as I am at work, all the gear here is on a production network, dont want to possibly disrupt that.  (Production...lol, if you call it that ).

Going to lab it up also when I get home tonight.

[Jack Leung]

when you do a switchport trunk allowed vlan it basically erases the old config and applies the new config hence the disruption. appending the ADD syntax keeps existing config but adds the additional.

[Richard Burts]

In my experience both commands, when done correctly and accurately, are pretty low impact. But the second command is designed specifically to add a VLAN and I believe that it is the best way to add a VLAN.

Part of my concern about just cut and paste and recreate the vlan allowed list is that the more entries there are to cut and paste the greater the opportunity to miss one, or to fat finger one, or to have some other unintended mistake which could possibly drop entries from the list.

HTH

Rick

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