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trikmik
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Joined: 06 Nov 2017
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PostPosted: Tue Nov 14, 2017 10:16 pm    Post subject: How to check dns Reply with quote

I want to prevent DNS poisoning, so I set openDNS in /etc/resolv.conf

How do I check what DNS is actually being used?
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szatox
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PostPosted: Tue Nov 14, 2017 11:06 pm    Post subject: Reply with quote

Setup tpdump/wireshark on 53/udp and inspect traffic when you resolve some domains.
Or block it on firewall (-I OUTPUT -j DROP -p udp --dport 53 -d <DNS IP> ) and check how long the query takes (Should fail after like 10 seconds to timeout). Obviously, you will have to revert that after testing.
Or just log and block all DNS traffic besides those IPs you trust.
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SP2340
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PostPosted: Thu Nov 16, 2017 6:46 pm    Post subject: Re: How to check dns Reply with quote

trikmik wrote:
I want to prevent DNS poisoning, so I set openDNS in /etc/resolv.conf

How do I check what DNS is actually being used?


You could check with dig or nslookup. Both show what server they queried for the answer. Look for 'SERVER:' in the answer.

As szatox stated if you are paranoid then just setup your firewall to only allow queries to the servers you trust.
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