cloud engineer
Here’s how to troubleshoot nameservers with dig.
dig hostname dig domain.com |
dig hostname dig domain.com
To test a specific nameserver.
dig @nameserver hostname dig @nameserver ip-address |
dig @nameserver hostname dig @nameserver ip-address
Other options.
dig hostname.domain.com +short dig hostname.domain.com +noall +answer dig @nameserver MX domain.com dig @nameserver AAAA domain.com |
dig hostname.domain.com +short dig hostname.domain.com +noall +answer dig @nameserver MX domain.com dig @nameserver AAAA domain.com
You can use the curl command to test if your load balancer is working as expected. The curl command will alternately and randomly access several instances in your load balancer. If you have 3 instances behind your load balancer, it will be cycled across all 3. The -m1 command means max time is set to 1 second.
while true; do curl -m1 [IP_ADDRESS]; done |
while true; do curl -m1 [IP_ADDRESS]; done
You can test a network port connection using the “nc” command on Linux and “telnet” on Windows.
Format:
$ nc -zv domain.com port
C:\> telnet domain.com port
$ nc -zv domain.com 80 Connection to domain.com 80 port [tcp/http] succeeded! |
$ nc -zv domain.com 80 Connection to domain.com 80 port [tcp/http] succeeded!
C:\> telnet -zv domain.com 80 Connecting To domain.com...Could not open connection to the host, on port 80: Connect failed |
C:\> telnet -zv domain.com 80 Connecting To domain.com...Could not open connection to the host, on port 80: Connect failed
For Telnet, if a connection is successful, it returns no message.