All netgear routers by default do not have telnet enabled. This feature needs to be unlocked. Existing tools do not work as in late 2014, Netgear decided to change the ports the commands needed to be sent over to unlock telnet from TCP port 23 to UDP port 23.
"The old Netgear Windows telnetEnable.exe sends probe packets to the router's TCP port 23. Thus, it is not compatible with firmware and routers Netgear introduced after early 2014, which require UDP port 23."
http://wiki.openwrt.org/toh/netgear/telnet.consoleHowever, a developer has modified the unlock tool in order for this to work. The exe file can be found on git hub.
How to Unlock Telnet.
1) Download the unlock tool from here
https://github.com/LuKePicci/NetgearTelnetEnable/blob/master/binaries/windows/telnetenable.exe2) Once downloaded run the following command telnetenable.exe {IP ADDRESS of D6400} {MAC ADDRESS of Router LAN Port} {user id} {password}
What you type should look similar to this
telnetenable.exe 192.168.1.1 000FB5A2BE26 admin helloworld
If you have done this correctly, you should now be able to use telnet.
3) On dslstats, select any netgear router - i think i selected the last one in the list.
4) Leave user ID and Password blank on DSLstats.
5) No other settings required.
Hope this helps.
Remember, each time you reboot the router, you will have to unlock telnet again.