在局域網中掃描一臺機器是否在線，或者某個端口在目標機器上是否開啓，
可以用這個命令方便的進行查詢。
在局域網中DHCP開啓的情況下，這個命令尤其有用，設想知道目標機器的MAC地址，
掃描得到結果後，即可以知道該機器的IP地址，不必反覆的跑離座位或者到服務器上去查找目標機器的IP地址。
nmap -v -sU 10.9.8.0/24 -p 1137
結果如下：
Host 10.9.8.217 appears to be up ... good.
Interesting ports on 10.9.8.217:
PORT STATE SERVICE
1137/tcp open unknown
MAC Address: 00:0E:09:AC:73:31 (Shenzhen XXX Software Co.)
Host 10.9.8.42 appears to be up ... good.
Interesting ports on 10.9.8.42:
PORT STATE SERVICE
1137/udp closed unknown
MAC Address: 00:0C:29:60:4A:A7 (VMware)
Host 10.9.8.71 appears to be up ... good.
Interesting ports on 10.9.8.71:
PORT STATE SERVICE
1137/udp closed unknown
MAC Address: 00:16:EC:B0:8A:33 (Elitegroup Computer Systems Co.)