一段 ping 命令的执行返回：

[[email protected] ~]# ping baidu.com
PING baidu.com (220.181.38.148) 56(84) bytes of data.
64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=1 ttl=49 time=35.9 ms
64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=2 ttl=49 time=67.4 ms
64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=3 ttl=49 time=37.6 ms
^C
--- baidu.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 35.947/47.022/67.444/14.457 ms
[[email protected] ~]# ping github.com
PING github.com (13.229.188.59) 56(84) bytes of data.
64 bytes from ec2-13-229-188-59.ap-southeast-1.compute.amazonaws.com (13.229.188.59): icmp_seq=1 ttl=42 time=121 ms
64 bytes from ec2-13-229-188-59.ap-southeast-1.compute.amazonaws.com (13.229.188.59): icmp_seq=2 ttl=42 time=119 ms
64 bytes from ec2-13-229-188-59.ap-southeast-1.compute.amazonaws.com (13.229.188.59): icmp_seq=3 ttl=42 time=126 ms
^C
--- github.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 119.436/122.369/126.585/3.069 ms
[[email protected] ~]# 

疑问的是 ping github 的返回中 ec2-13-229-188-59.ap-southeast-1.compute.amazonaws.com 是拿来的，ping 返回的数据格式怎么理解？

IP 地址 Reverse DNS 的结果

CNAME

错了，这么长还带 IP 的是 rDNS

这个叫做 PTR (DNS Pointer Record)记录
59.188.229.13.in-addr.arpa name = ec2-13-229-188-59.ap-southeast-1.compute.amazonaws.com.