How to Test a DNS Port

Written by dave wilson
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How to Test a DNS Port
Verify firewall DNS ports are open and not blocking Internet traffic (Internet security image by Nicemonkey from Fotolia.com)

The DNS, or Domain Name Service, enables the use of human readable hostnames on networks such as the Internet by managing a database of hostname-to-IP address mappings and resolving the hostname-to-IP address mappings when computers query the DNS service. Hosting a DNS on the Internet requires that UDP port 53 or TCP port 53 be configured on the firewall that protects the DNS server to forward all requests directed to UDP port 53 to the private network IP address of the DNS server. Test to verify that UDP port 53 is open on the firewall and ready to accept and forward DNS queries to the DNS server.

Skill level:
Easy

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Instructions

  1. 1

    Open a web browser and go to the "Ping.eu Port Check" web page (see Resources). Type the IP address of the Internet interface of the firewall into the "IP address or host name" field. Type "53" into the "Port number" field.

  2. 2

    Click the "Go" button. If the test page reports "open," then the firewall is configured to allow traffic on DNS port 53. If the test page reports "closed," then change the firewall configuration to open port 53 and forward traffic to the DNS server.

  3. 3

    Go to the "DynDNS Open Port Tool" web page (see Resources). Type the IP address of the Internet interface of the firewall into the first field listed by "Host and Port." Type "53" into the second field listed by "Host and Port."

  4. 4

    Click the "Send" button. If the test page reports that the port is "open," then the firewall is configured to allow connections on DNS port 53. If the test page reports "timed out," then change the firewall configuration to open port 53 and forward traffic to the DNS server.

  5. 5

    Go to the "TestMy.net:Whois, DNS Lookup & Port Check" website (see Resources). Type the IP address of the firewall Internet interface into the box located by the "Run Query" button. Select the "Check port" radio button, then type "53" into the box located by the "Check port" radio button.

  6. 6

    Click the "Run Query" button. If the test page reports "Port 53 is open and accepting connections," then the firewall is configured to allow connections on DNS port 53. If the test page reports "Port 53 does not appear to be open," then change the firewall configuration to open port 53 and forward traffic to the DNS server.

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