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outbound access to port 53 dns

Posted on 2013-11-27
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Last Modified: 2013-11-30
Hi,
one of the new apps we recently installed requested outbound access to port 53 be opened on firewall.  Since this port is used for dns, wouldnt this port already be opened or else dns would not be working for network?  I have tested to check if an inbound port is open by using canyouseeme.org but how would i test if port 53 is open?  If i wanted to test 443 for instance i would try to access an https website and if unable then i know port 443 not open for outbound so how would  i do this for port 53?  Thanks.
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Question by:dankyle67
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Tony Massa earned 1000 total points
ID: 39682786
Not necessarily.  Many companies only allow DNS from internal DNS caching servers, like domain controllers or BIND DNS servers.  Internal servers would generally forward DNS queries to outside DNS to servers that are specifically allowed out, and not for all internal clients and servers.

The app may only need to be able to resolve DNS on the outside, so you probably don't have to open directly to the internet anyway.  If your server can resolve external DNS, you're probably okay.

If you want to test DNS externally, you can nslookup from the server to an external DNS server, like google (8.8.8.8)

C:\>nslookup
Default Server:  myDNS.server.com
Address:  x.x.x.x

> server 8.8.8.8
Default Server:  google-public-dns-a.google.com
Address:  8.8.8.8

> set type=a
> www.google.com
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
Name:    www.google.com

Addresses:  74.125.228.49
          74.125.228.50
          74.125.228.52
          74.125.228.51
          74.125.228.48

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by:Sandeshdubey
Sandeshdubey earned 1000 total points
ID: 39683317
Check the dns forwarder on DNS if not set  set the same.Also ensure correct dns setting on DC and client as this.http://abhijitw.wordpress.com/2012/03/03/best-practices-for-dns-client-settings-on-domain-controller/

Run nslookup on client computer to resolve external query and check.
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