[OpenWrt Wiki] ASUS RT-N56U
https://openwrt.org/toh/asus/rt-n56u27.03.2017 · OpenWrt Version Supported UPC EAN Box Model Specific Notes ; A1 / v1 : 2011 : 14.07 Barrier Braker : 610839332465 : 4719543332467 : matte, marked: “RT-N56U Wireless-N Dual-band Gigabit Router” Known as RT-N56U A1; WAN & LAN 1-4 RJ45 sockets contain LED's : B1 / v2 : May 2015 : Unsupported : 610839332472 : 4719543332474
[OpenWrt Wiki] ASUS RT-N66U
https://openwrt.org/toh/asus/rt-n66u06.11.2014 · ASUS RT-N66U Devices with Broadcom WiFi chipsets have limited OpenWrt supportability (due to limited FLOSS driver availability for Broadcom chips). Consider this when chosing a device to buy, or when deciding to flash OpenWrt on your device because it is listed as supported. See Broadcom WiFi for details. Supported Versions Unsupported Functions