環境ORACLE Linux8（其他環境也可以參考這個步驟）

1.測試使用TNSNAMES tnsping無法連接到主機

[oracle@dguard2 admin]$ tnsping dguard

TNS Ping Utility for Linux: Version 19.0.0.0.0 - Production on 11-JUL-2022 10:03:44

Copyright (c) 1997, 2019, Oracle. ?All rights reserved.

Used parameter files:
/u01/app/oracle/product/19.3.0/dbhome_1/network/admin/sqlnet.ora

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.43.92)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = dguard)))
TNS-12543: TNS:destination host unreachable

2.查看主機是否可以Ping 通，結果是可以PING 通

[oracle@dguard2 admin]$ ping 192.168.43.92
PING 192.168.43.92 (192.168.43.92) 56(84) bytes of data.
64 bytes from 192.168.43.92: icmp_seq=1 ttl=64 time=0.530 ms
64 bytes from 192.168.43.92: icmp_seq=2 ttl=64 time=0.431 ms
64 bytes from 192.168.43.92: icmp_seq=3 ttl=64 time=0.408 ms
64 bytes from 192.168.43.92: icmp_seq=4 ttl=64 time=0.255 ms
^C
--- 192.168.43.92 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3108ms
rtt min/avg/max/mdev = 0.255/0.406/0.530/0.098 ms
[oracle@dguard2 admin]$
?

3.直接使用IP連接數據庫看看是否可以鏈接，如果這樣可以連接可能是TNS設置問題。結果是同樣報ORA-12543
[oracle@dguard2 ~]$ sqlplus sys/password@192.168.43.92:1521/dguard

SQL*Plus: Release 19.0.0.0.0 - Production on Mon Jul 11 10:06:54 2022
Version 19.3.0.0.0

Copyright (c) 1982, 2019, Oracle. ?All rights reserved.

ERROR:
ORA-12543: TNS:destination host unreachable

4.查看是否SQLNET配置問題，SQLNET包含了所有可以使用的方式，不是SQLNET問題[oracle@dguard admin]$ cat sqlnet.ora
# sqlnet.ora Network Configuration File: /u01/app/oracle/product/19.3.0/dbhome_1/network/admin/sqlnet.ora
# Generated by Oracle configuration tools.

NAMES.DIRECTORY_PATH= (TNSNAMES, ONAMES, HOSTNAME)

5.查看是否Oralce相應端口未開放，結果是LISTNER 正在1521監聽TCP協議的連接

[root@dguard ~]# netstat ?-anop |grep 1521
tcp ? ? ? ?0 ? ? ?0 192.168.43.92:1521 ? ? ?0.0.0.0:* ? ? ? ? ? ? ? LISTEN ? ? ?3599/tnslsnr ? ? ? ? off (0.00/0/0)
unix ?2 ? ? ?[ ACC ] ? ? STREAM ? ? LISTENING ? ? 53432 ? ?3599/tnslsnr ? ? ? ? /var/tmp/.oracle/sEXTPROC1521
[root@dguard ~]#

6.查看防火墻狀態，防火墻狀態為開啟狀態
[root@dguard init.d]# systemctl status firewalld.service
● firewalld.service - firewalld - dynamic firewall daemon
? ?Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
? ?Active: active (running) since Mon 2022-07-11 09:44:32 CST; 29min ago
? ? ?Docs: man:firewalld(1)
?Main PID: 987 (firewalld)
? ? Tasks: 2 (limit: 22958)
? ?Memory: 30.9M
? ?CGroup: /system.slice/firewalld.service
? ? ? ? ? ?└─987 /usr/libexec/platform-python -s /usr/sbin/firewalld --nofork --nopid

Jul 11 09:44:31 dguard systemd[1]: Starting firewalld - dynamic firewall daemon...
Jul 11 09:44:32 dguard systemd[1]: Started firewalld - dynamic firewall daemon.
Jul 11 09:44:33 dguard firewalld[987]: WARNING: AllowZoneDrifting is enabled. This is considered an insecure configuration option. It will be removed in a future release. Please consider d>

7.關閉防火墻并檢查狀態
[root@dguard init.d]# systemctl stop firewalld.service
[root@dguard init.d]# systemctl status firewalld.service
● firewalld.service - firewalld - dynamic firewall daemon
? ?Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
? ?Active: inactive (dead) since Mon 2022-07-11 10:14:07 CST; 9s ago
? ? ?Docs: man:firewalld(1)
? Process: 987 ExecStart=/usr/sbin/firewalld --nofork --nopid $FIREWALLD_ARGS (code=exited, status=0/SUCCESS)
?Main PID: 987 (code=exited, status=0/SUCCESS)

Jul 11 09:44:31 dguard systemd[1]: Starting firewalld - dynamic firewall daemon...
Jul 11 09:44:32 dguard systemd[1]: Started firewalld - dynamic firewall daemon.
Jul 11 09:44:33 dguard firewalld[987]: WARNING: AllowZoneDrifting is enabled. This is considered an insecure configuration option. It will be removed in a future release. Please consider d>
Jul 11 10:14:07 dguard systemd[1]: Stopping firewalld - dynamic firewall daemon...
Jul 11 10:14:07 dguard systemd[1]: firewalld.service: Succeeded.
Jul 11 10:14:07 dguard systemd[1]: Stopped firewalld - dynamic firewall daemon.
lines 1-13/13 (END)

8.TNSPING 看看是或否可以連接，結果是可以正常的TNSPING 數據庫了

[oracle@dguard2 admin]$ tnsping dguard

TNS Ping Utility for Linux: Version 19.0.0.0.0 - Production on 11-JUL-2022 10:19:41

Copyright (c) 1997, 2019, Oracle. ?All rights reserved.

Used parameter files:
/u01/app/oracle/product/19.3.0/dbhome_1/network/admin/sqlnet.ora

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.43.92)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = dguard)))
OK (10 msec)

?