What is port lockdown?

Port Lockdown controls what types of connections will be allowed to the self IP based on protocol and port. You can find a great overview of Port Lockdown behavior here, along with recommendations on how best to use this feature.

eesun,

F5 publishes a K article describing this in great detail. https://support.f5.com/csp/article/K17333

In short, it is a security feature associated with self-IPs that allows you to control what ports and protocols are permitted. I do not know your specific scenario, but a self-IP associated with an external VLAN would probably not be something you would want to set up with a port lockdown of say "allow-default" as that would expose TMUI management. You may want to set something like that to "allow none" or customize the ports allowed. For example, if you are using GTM/DNS and you need the GTM/DNS iQuery functionality to your self-IP on VLAN external, then you would use "allow custom" to specify ports and protocols to allow. I hope this helps!