--auto analysis

[Andy Whitcroft]

[Mark: this discussion was ongoing and ties directly to your comments
in the other document.]

Configuring Fan Networking is fraught with complexity.  The network
prefixes must be chosen appropriately for the underlay addresses in use
and for the possible overall address ranges in the current environment.
For local networks the address ranges are fairly easily determined from
the address range itself (RFC1918 addresses have defined boundaries).
However these address ranges are commonly used in other environments as
private addresses, such as in a private network in a cloud environment.
Those environments also place different constraints on the addresses
depending on networking mode.  To ease adoption in those environments it
is sensible to try and provide sensible opinionated default Fan
Networks.

To this end we have performed a detailed analysis of the big three clouds
(AWS, GCE and Azure), as well as considering local network envionrments.
Based on this analysis we have put together automated detection of these
environments and determined sensible underlay and overlay prefix sizes
to provide a reasonably consistent overlay address distribution per
underlay host.

The current state of the art is documented in this document.  Please
feel free to comment on the document:

https://docs.google.com/document/d/1sHMfE-jzYNEXt_mPqOcg1And7ei9nRmlYTIlsdh-pVo/

-apw