Which servers are contacted by a SIP phone during the auto provisioning process upon power-up?

During the auto provisioning process upon power-up, a SIP phone is designed to contact various servers to retrieve its configuration settings. The key servers involved in this process include SIP (Session Initiation Protocol), DNS (Domain Name System), and potentially a Boot server.

The SIP server is essential for establishing communication within the VoIP infrastructure, as it handles signaling for initiating, maintaining, and terminating voice calls. The DNS server is crucial for translating human-readable domain names into IP addresses, which allows the SIP phone to locate the correct servers on the network.

The term "Boot" may refer to the boot server, which supports the booting process of devices by providing necessary configurations or software through protocols like TFTP (Trivial File Transfer Protocol) or HTTP. When a device is powered on, it might need to fetch its initial configuration files, and the boot server plays a role in this.

In summary, the correct choice highlights the collective involvement of the SIP and DNS servers alongside the Boot server during the initial setup of a SIP phone, ensuring proper configuration and functionality in the VoIP environment. The other options do not account for all necessary protocols and servers involved in this crucial phase, leading to a less comprehensive understanding of the auto provisioning process.