Verify the IP and DNS traffic

Verify the IP and DNS traffic

This section describes how to troubleshoot issues with the IP and DNS traffic on a VM.

To verify the IP traffic:

  1. Log in to the VM in question.

  2. Ping any IP, for example, Google DNS 8.8.8.8:

    ping 8.8.8.8 -c 3
    

    Example of system response:

    PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
    64 bytes from 8.8.8.8: icmp_seq=1 ttl=59 time=4.12 ms
    64 bytes from 8.8.8.8: icmp_seq=2 ttl=59 time=4.37 ms
    64 bytes from 8.8.8.8: icmp_seq=3 ttl=59 time=4.03 ms
    
    --- 8.8.8.8 ping statistics ---
    3 packets transmitted, 3 received, 0% packet loss, time 2002ms
    rtt min/avg/max/mdev = 4.038/4.180/4.377/0.161 ms
    
  3. If pinging does not work, use the traceroute command on the same address to identify the issue.

To verify the DNS traffic:

  1. Log in to the VM in question.

  2. Run the following command:

    dig google.com
    

    Example of system response:

    ; <<>> DiG 9.9.5-3ubuntu0.16-Ubuntu <<>> google.com
    ;; global options: +cmd
    ;; Got answer:
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15428
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 5
    
    ;; OPT PSEUDOSECTION:
    ; EDNS: version: 0, flags:; udp: 4096
    ;; QUESTION SECTION:
    ;google.com.                    IN      A
    
    ;; ANSWER SECTION:
    google.com.             300     IN      A       216.58.201.110
    
    ;; Query time: 20 msec
    ;; SERVER: 172.17.32.194#53(172.17.32.194)
    ;; WHEN: Thu Nov 23 14:14:41 UTC 2017
    ;; MSG SIZE  rcvd: 191
    

    In the output above, the VM resolved the google.com domain to the IP address 216.58.201.110.

  3. If the domain to the IP address is not resolvable:

    1. Run the following command to identify when the resolve of the DNS server stops:

      dig google.com +trace
      
    2. Dig a different server name. For example:

      dig  google.com @8.8.8.8