You can customize your cache announcement message by setting this directive to a file containing additional information. For example, you can include information about your upstream service provider, telephone number, other caches that you peer with, etc.
Announcement messages are sent via UDP, so this file shouldn’t be too large. Some systems can’t send or receive UDP messages larger than 9 KB. Furthermore, larger messages are more likely to be dropped before reaching their destination.
announce_period, announce_host, announce_port