Note: Remember to make a copy of all current ip settings before proceeding.

From ATT's page: 

https://www.att.com/Common/storefront/resources/pdf/att_bridged_mode_vs_ip_passthrough_nov2012_v3.pdf

the bold text says: "Note: Remember to make a copy of all current ip settings before proceeding."

but does not give a link, nor explain how to make that copy.

Is this copying done by causing my AT&T Arris NVG599 device to make one via some function like "Export"? Or am I do make a handwritten note of the current ip settings? And which settings and why would using passthrough change them, please?