Quick Question regarding VLANs and Trunking

[jpeterson6]

I've been tasked to allow only specific VLANs through a trunk connecting my Core machine (6509) to a switch loaded with servers.

The intent is to only allow traffic through the trunk that needs to be there.

My question is: When I run the command 'switchport trunk allowed vlan <vlan list>', will traffic be interrupted while the change is applied?

We have some very sensitive traffic that will be affected by even a slight interruption (ie, ODBC/SQL), so even a lost ping could cause some issues.

Thanks.

[John Blakley · Accepted solution]

Generally, you won't notice any disruption. The only time that I've seen it is when changing encapsulation types. I would script what you want, and then paste it in.

switchport trunk encapsultation dot1q

switchpo mode trunk

swit trunk allowed vlan add 1,10,15,25

Even though, in theory, you shouldn't see anything, I would create downtime if it's that sensitive.

Oh, and if the port is already in trunking mode and is passing traffic, then the only way that you would create downtime by adding new vlans is to remove a vlan that belongs on that trunk. Otherwise, you won't notice anything if you don't have to change the port modes.

HTH,

John

[jpeterson6]

Good to know, thanks for the clarification.