Which IP address must be reachable by a WAN Edge device for the ZTP process to work?

During the Zero Touch Provisioning (ZTP) process, Cisco WAN Edge devices attempt to resolve a specific FQDN (e.g., ztp.viptela.com) to find the ZTP server. This FQDN is typically hosted on a public DNS server, and historically, Cisco's ZTP infrastructure often used 4.4.4.4 as a DNS server in initial ZTP configurations for resolution.

172.16.1.1 is a private IP address and generally not reachable from the internet for ZTP services.

8.8.8.8 is Google's public DNS server, which devices can typically reach for DNS resolution during ZTP, but the specific address 4.4.4.4 is the historically referenced one in Cisco's ZTP documentation for initial contact.

10.1.1.1 is a private IP address and generally not reachable from the internet for ZTP services.