Client:
./clt -n -1 [for apply for a ip address and enter normally renew period (t1 expires and successful lease renew).]
./clt -n -2 [for apply for a ip address and enter normally renew period (t2 expires).]
./clt -u [for apply for a ip address and enter normally renew period (t2 expires).]
./clt -r [for release a ip addr.]
./clt -inform [for inform.]
Server:
./svr [For normal server.]
./svr -n [When client applies to renew its lease, send NAK]