3.4.4 Higher-Layer Triggered Events
Netlogon responds to a few higher-layer triggered events.
Transport being added or removed. Whenever a new transport becomes available or unavailable, Netlogon MUST incorporate the transport event and use the DC Locator components ([MS-ADTS] section 6.3.6) to make sure that it has a valid domain controller to connect to.
If an application calls a Netlogon method and a secure channel is not currently set up, a secure channel MUST be established before the RPC call to the server is made.