Ping domain name error unknown host, NSLOOKUP / system d-resolve can be resolved normally, how to Ping the public network address?

Abnormal phenomenon

ping Domain name error unknown host,nslookup/systemd-resolve It can be parsed normally ,ping Public address communication .

[email protected]:/etc# ping baidu.com
ping: unknown host baidu.com

[email protected]:/etc# nslookup www.baidu.com
Server:         192.168.61.200
Address:        192.168.61.200#53

Non-authoritative answer:
www.baidu.com   canonical name = www.a.shifen.com.
Name:   www.a.shifen.com
Address: 183.232.231.174
Name:   www.a.shifen.com
Address: 183.232.231.172

[email protected]:/etc# systemd-resolve www.baidu.com
www.baidu.com: 183.232.231.172
               183.232.231.174
               (www.a.shifen.com)

-- Information acquired via protocol DNS in 74.1ms.
-- Data is authenticated: no

[email protected]:/etc# ping 183.232.231.174
PING 183.232.231.174 (183.232.231.174) 56(84) bytes of data.
64 bytes from 183.232.231.174: icmp_seq=1 ttl=54 time=33.4 ms
64 bytes from 183.232.231.174: icmp_seq=2 ttl=54 time=32.7 ms
64 bytes from 183.232.231.174: icmp_seq=3 ttl=54 time=33.9 ms
64 bytes from 183.232.231.174: icmp_seq=4 ttl=54 time=45.0 ms
^C
--- 183.232.231.174 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3013ms
rtt min/avg/max/mdev = 32.723/36.281/45.043/5.077 ms

Outliers that need to be checked

1、 Check /etc/nsswitch.conf

[email protected]:~# cat /etc/nsswitch.conf 
# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.

passwd:         compat
group:          compat
shadow:         compat
gshadow:        files

hosts:          files dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

Check hosts That's ok , Is it files dns,files Said the use of /etc/hosts and /etc/network The configuration file ,dns Said the use of /etc/resolv.conf In the document DNS Address resolution .

ping Program resolution of domain name depends on C Functions in the library gethostbyname() and gethostbyaddr(), Corresponding configuration file /etc/nsswitch.conf Medium hosts Configuration item .nslookup Direct use /etc/resolv.conf Medium DNS Domain name resolution , Therefore, it is not affected by this document .

2、 Check /etc/resolv.conf File permissions

# Ubuntu System 
# Ubuntu In the system resolv.conf For a soft connection , If there is a problem , You can manually rebuild the soft connection ln -s /etc/resolvconf/run/resolv.conf /etc/resolv.conf
#  Check carefully after reconstruction /etc/resolvconf/run/resolv.conf Whether the configuration is correct 
[email protected]:~# ll /etc/resolv.conf 
lrwxrwxrwx 1 root root 29 Apr 26 16:20 /etc/resolv.conf -> ../run/resolvconf/resolv.conf

# CentOS System 
[[email protected] ~]$ ll /etc/resolv.conf
-rw-r--r--. 1 root root 61 Nov  3  2021 /etc/resolv.conf

If resolv.conf File has no read permission , Can also cause ping uknown host The situation of .