02-27-2009 06:52 PM - edited 03-11-2019 07:58 AM
is it necessary to allow both UDP and TCP port 53 for accessing DNS servers through a firewall access-list?
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02-27-2009 07:49 PM
tcp/53 is used for zone-transfers. if you are doing just normal queries udp/53 will suffice.
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02-27-2009 07:51 PM
thanks vikram.
02-27-2009 08:03 PM
Here is another reason why tcp/53 is used "A client can use TCP whenever it wants, and has to use TCP when the response it gets via UDP is truncated because it is too long"
03-04-2009 08:49 AM
tcp/53 is also used for large transfers.
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