FTP passthrough
Enable NAT passthrough for FTP using kmod-nf-nathelper.
opkg update opkg install kmod-nf-nathelper service firewall restart
SIP passthrough
Enable NAT passthrough for SIP, PPTP, GRE, etc. using kmod-nf-nathelper-extra.
opkg update opkg install kmod-nf-nathelper-extra service firewall restart
RTSP passthrough
Enable NAT passthrough for RTSP using