The cracked binary disables the master server.
The no delay binary changes the minimum required master server offline time before you can connect to a original server (from ~30 minutes to 5 seconds).
The iptables solution blocks the reject message for cracked players (requires the right server ports and root access).
The best solution is installing libcod and setting sv_cracked to 1.
For more information see the libcod section:
https://killtube.org/forumdisplay.php?44-libcod