使用lsof或者netstat命令只能查看是否有upd端口处于监听模式，无法查看是否有upd数据在传输，可以使用tcmpdump查看upd流量

a主机ip地址为192.168.103.174上监听udp端口155  

Testdbstd:~ # nc -lku 155  

在a主机开启抓包

Testdbstd:~ # tcpdump -i eth0 -n udp

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes

09:56:01.560516 IP 192.168.103.175.45670 > 192.168.103.174.155: UDP, length 10

10:00:50.342348 IP 192.168.103.175.24938 > 192.168.103.174.155: UDP, length 4

b主机向a主机传输信息

echo "bbb"| nc -u 192.168.103.174 155