Full packet Capture on DD-WRT

[ZF]

iptables -A PREROUTING -t mangle -j ROUTE --gw <repository address> --tee
iptables -A POSTROUTING -t mangle -j ROUTE --gw <repository address> --tee

Alternatively, to selectively mirror:
Traffic to target:
iptables -A PREROUTING -t mangle -d <target> -j ROUTE --gw <repo> --tee
iptables -A POSTROUTING -t mangle -d <target> -j ROUTE --gw <repo> --tee
Traffic from target:
iptables -A PREROUTING -t mangle -s <target> -j ROUTE --gw <repo> --tee
iptables -A POSTROUTING -t mangle -s <target> -j ROUTE --gw <repo> --tee

On target machine:
tcpdump -i <interface> -s 65535 -w <some-file>

[ZF]

To verify
iptables -t mangle -L -v -n

ASUS AC66U Firmware supports tcpdump and NTFS filesystem by default
dd-wrt-25697-Asus_RT-AC66U.trx

ftp.dd-wrt.com/others/eko/BrainSlayer-V24-preSP2/2014/