在我的服务器（CentOS7.2，地址是103.193.202.2）上，我运行iperf服务器：
# iperf -u -s
------------------------------------------------------------
Server listening on UDP port 5001
Receiving 1470 byte datagrams
UDP buffer size: 208 KByte (default)
------------------------------------------------------------
在我的 Mac 上，我使用下面的命令来测试我的服务器。
$ iperf -u -c 103.193.202.2 -b 100M -P 5
------------------------------------------------------------
Client connecting to 103.193.242.2, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size: 9.00 KByte (default)
------------------------------------------------------------
[ 7] local 192.168.1.3 port 58906 connected with 103.193.242.2 port 5001
[ 6] local 192.168.1.3 port 63984 connected with 103.193.242.2 port 5001
[ 4] local 192.168.1.3 port 62739 connected with 103.193.242.2 port 5001
[ 5] local 192.168.1.3 port 62128 connected with 103.193.242.2 port 5001
[ 8] local 192.168.1.3 port 59654 connected with 103.193.242.2 port 5001
[ ID] Interval Transfer Bandwidth
[ 7] 0.0-10.0 sec 4.42 MBytes 3.70 Mbits/sec
[ 7] Sent 85471 datagrams
[ 6] 0.0-10.0 sec 7.36 MBytes 6.17 Mbits/sec
[ 6] Sent 85470 datagrams
[ 4] 0.0-10.0 sec 4.41 MBytes 3.70 Mbits/sec
[ 4] Sent 85470 datagrams
[ 5] 0.0-10.0 sec 7.46 MBytes 6.25 Mbits/sec
[ 5] Sent 85468 datagrams
[ 8] 0.0-10.0 sec 8.22 MBytes 6.89 Mbits/sec
[ 8] Sent 85469 datagrams
[SUM] 0.0-10.0 sec 31.9 MBytes 26.7 Mbits/sec
[ 4] WARNING: did not receive ack of last datagram after 10 tries.
[ 8] WARNING: did not receive ack of last datagram after 10 tries.
[ 6] WARNING: did not receive ack of last datagram after 10 tries.
[ 7] WARNING: did not receive ack of last datagram after 10 tries.
[ 5] WARNING: did not receive ack of last datagram after 10 tries.
你可以看到我的 Mac 上有打印件WARNING: did not receive ack of last datagram after 10 tries.
，但在我的服务器中我也没有打印件。为什么我的测试失败了？