From the ChangeLogs
What's new in 6.17 (2014-Jul-18 15:14):
*) CCR1009 - fixed crash, only affects CCR1009;
What's new in 6.16 (2014-Jul-17 13:12):
*) 802.11ac support added in wireless-fp package for QCA9880/9882 rev2 (-BR4A) chips;
*) ip cloud now allows to set which IP to use - detected (public) or local (private);
*) l2tp, pptp, pppoe - fixed possible packet corruption when encryption was enabled;
*) ovpn - fixed ethernet mode;
*) certificates - use SHA256 for fingerprinting;
*) ipsec - fix AH proposal and problem when sometimes policy was not generated;
*) snmp - support AES encryption (rfc3826);
*) l2tp server: added option to enable IPsec automatically;
*) poe-out: added power-cycle-ping and power-cycle-interval settings;
*) gps - increased retry duration to 30 seconds;
*) time - on routerboards, current time is saved in configuration on reboot
and on clock adjustment, and is used to set initial time after reboot;
*) sntp - disabling/enabling client was causing dynamic-servers to be ignored
(bug introduced in 6.14);
*) CCR - fixed rare file system corruption when none
of configuration could be changed or some of it disappeared;
*) ipsec - allow multiple encryption algorithms per peer;
*) email - support tls only connections;
*) smb - fixed usb share issues after reboot
*) snmp - fix v3 protocol time window checks;
*) updated timezone information;
*) quickset - added VPN settings for HomeAP mode;
*) latency improvements on CCR devices;