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Comment by atkbrah | Hacker News Reader

It's like one of the most common user errors with cisco cli. When you want to add an interface to a vlan you would type:

  switchport trunk allowed vlan add $vlan

But if you by accident omit add keyword you would replace all interface vlans with $vlan

  switchport trunk allowed vlan $vlan

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At least in that case the important keyword isn't placed at the end (i.e. you would get an error if you merely typed ` switchport trunk allowed vlan add`)

IIRC that's like "groupadd" on Linux distros, if you don't add a switch it replaces all that users groups.

...and, if especially unlucky, that would be the trunk you're using to connect to that switch.

Which is why you usually have a seperate OOB network for logging into switches and routers.

If it's very mission critical, even an entire seperate cable infrastructure for OOB is not uncommon.

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