check DNS resolution validity in batch
Article ID: 423252
Updated On:
Products
Issue/Introduction
It is very important to check DNS resolution validity. In KB 423200, there is a script to check DNS resolution. That is a good script, but it can only check one FQDN/IP address . We need a script to check multiple FQDNs in batch .
Environment
vCenter Server
Esxi
and Linux
Cause
Found the advanced_check_dns_batch.sh file in attachment.
1) It compares the result of nslookup and getent, if the results are different, it means an inconsistency is found.
2) This script also compares the reverse resolution ( IP to FQDN) .
Resolution
In attachment, there is an advanced_check_dsn_batch.txt file.
The syntax is:
./advanced_check_dsn_batch.sh a.txt
In a.txt, there are multiple hostnames(FQDN)
Example:
a) In a.txt file,
host1.example.com
host2.example.com
host3.example.com
host77.example.com
b) Run the script:
# ./advanced_check_dsn_batch.sh a.txt
HOSTNAME SYSTEM IP DNS IP STATUS
-------------------------------------------------------------------------------
host1.example.com 192.168.99.1 192.168.99.1 OK
↳ Reverse Check: Sys[host1.example.com] | DNS[host1.example.com]
host2.example.com 192.168.99.2 192.168.99.2 OK
↳ Reverse Check: Sys[host2.example.com] | DNS[host2.example.com]
host3.example.com 192.168.99.3 192.168.99.3 OK
↳ Reverse Check: Sys[host3.example.com] | DNS[host3.example.com]
host77.example.com -- 127.0.0.1#53 MISMATCH
host1,host2,host3 are OK, but host77 is NG.
Tips:
In some cases, DNS server may return more than 1 IP addresses for a single FQDN. Only 1 IP address is correct, and other IP addresses are invalid.
For that case, run this script for multiple times, it may catch the invalid IP address.
But if the script is executed only once , and the correct IP address is returned, we may missed the DNS resolution issue. So do please run the script for multiple times.
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