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Forum Discussion
Wifi security code for Model No. R6400-100NAS
Netgear AC1750 SMART WIFI ROUTER 802.11ac Dual Band Gigabits
There's a support site with access to manuals, firmware, install guides, etc.
Go to https://www.netgear.com/support/
Type in your model number and from there it'll take you to the above.
Its a great resource to start with.