Does DNS use TCP or UDP or both?
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Answer / sathyender
TCP is a connection-oriented protocol and it requires data
to be consistent at the destination and UDP is
connection-less protocol and doesn't require data to be
consistent or don't need a connection to be established with
host for consistency of data.
UDP packets are smaller in size. Can't be greater then 512
bytes. So any application needs data to be transffered
greter than 512 bytes uses TCP
We often discuss why services use both the protocols i.e.
TCP and UDP. These services can also realy on TCP instead of
UDP because TCP is a connection-oriented protocol whereas
UDP is connection-less! then why use UDP?
For example, DNS uses both TCP and UDP for valid reasons
described below. Note that UDP messages are not larger than
512 Bytes and are trucncted when greater than this size. So
DNS uses TCP for Zone transfer and UDP for name queries
either regular (primary) or reverse. UDP can be used to
exchange small information whereas TCP must be used to
exchange information larger than 512 bytes. If a client
doesn't get response from DNS it must retransmit the data
using TCP after 3-5 seconds of interval.
| Is This Answer Correct ? | 95 Yes | 9 No |
Answer / smruti
DNS uses both TCP as well as UDP.
One more thing I want to add, why UDP is used though TCP is
connection oriented and better, that UDP is faster than TCP.
| Is This Answer Correct ? | 30 Yes | 5 No |
Answer / jai
Sathyender is not wrong about the scenario when DNS uses TCP.
Halon is correct by saying UDP is not limited to 512 bytes
of data.
DNS uses UDP for normal communications. However, check this
detail in RFC 1035
2.3.4. Size limits
Various objects and parameters in the DNS have size limits.
They are listed below. Some could be easily changed,
others are morefundamental.
labels 63 octets or less
names 255 octets or less
TTL positive values of a signed 32 bit number.
UDP messages 512 octets or less
So, the DNS messages can not exceed 512 bytes and when that
happens, the DNS server truncate the data and only send 512
bytes with a TRUNCATED BIT set in the header.
When the DNS client sees this TRUNCATED BIT, it comes to
know that the data is more than 512 bytes which can not be
received using UDP. Then, it switches over to TCP and sends
the same request on TCP.
Hope this clarifies.
| Is This Answer Correct ? | 16 Yes | 2 No |
Answer / mubashir
Halon, You are absolutley right. DNS uses UDP just because
it requires a great speed in execution. Packets Loss is not
a big deal. But it should use UDP instead of TCP.
| Is This Answer Correct ? | 15 Yes | 3 No |
Answer / majid malik
My name is Majid Malik. I know that DNS use TCP and UDP but
TEST INSIDE 356Q Dumps Says only one Choice to Select.
They give us to choices to select both.
Thanks
Majid Malik
| Is This Answer Correct ? | 2 Yes | 1 No |
Answer / prince
I am more convinced with the explanation of CURRY. DNS uses
both protocol but the UDP suits the best
thanks to all
| Is This Answer Correct ? | 0 Yes | 0 No |
Answer / kyle
Windows DNS uses both, and is more in line with proper standards than it once was. For instance, the port ranges are now set to international standards since Server 2008.
This is a great site about Windows DNS and ports: http://technet.microsoft.com/en-us/library/dd197515(v=ws.10).aspx
Also, some have said TFTP has file size limits, which is generally no longer true. TFTP now is capable of sending files of essentially unlimited size, given a stable enough connection. "If the server and client support block number wraparound, file size is essentially unlimited." Source: http://en.wikipedia.org/wiki/Trivial_File_Transfer_Protocol
| Is This Answer Correct ? | 0 Yes | 0 No |
Answer / curry muncher
UDP since its nature of connection is the best possible over
TCP. Packet loss is not an issue but the speed at which the
information is obtained is critical.
| Is This Answer Correct ? | 0 Yes | 2 No |
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