How do I determine the IP bandwidth of caldav.icloud.com for firewall registration?

CalDAV (Calendar DAV) is a protocol that allows users to manage calendar data, such as events, tasks, and reminders, over a network. The bandwidth needs are very small, unless you manage thousands of enterprise users or edu users. A typical calendar event is just a a few hundred bytes. I would say almost negligible compared to other network use.

There's no single bandwidth requirement for using caldav.icloud.com. The amount of data transferred will vary based on individual usage and the size of your calendar data.

Factors affecting bandwidth:

• Number of calendars: More calendars mean more data is synchronized.
• Frequency of updates: Frequent updates (e.g., new events, changes to existing events) will result in more data being transferred.
• Size of calendar data: Large calendar files, especially if they include attachments, will consume more bandwidth.

I don’t think there a standard value without investigating your specific situation and needs.