Tuesday, May 26, 2015

VLAN cisco reservation internal usage ( thoughts )

With Vlan IDs  we have some that we  should be avoid & this issue bound to come up in big networks with hundreds if not thousands of vlans.

The following show command  under IOS/NX-OS will display these internal usage vlans;


show vlan internal  usage

If you try to configure a vlan that's used internally, you will have an error similar to the  below.

Now luck has it that cisco has created a means for reserving  vlans. It's sometime best to apply this practices in big SP/ENTERPRISE networks to avoid design issues  that could later conflicts with a reserved vlan.

Our socpuppets general thought has always been to craft vlans under the 4K range,  and build a vlan allocation sheet that you SHOULD always review b4 vlan allocations.

The "vlan internal  allocation policy ascending" or "vlan internal  allocation policy descending" commands can help in determining the internal vlan allocation methods.

NOTE: I believe this is a IOS command and not widely deploy under most  NX-OS switches.

Ken Felix
NSE ( Network Security Expert) and Route/Switching Engineer.
kfelix  -----a----t---- socpuppets ---dot---com

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