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Answer Posted / 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 |
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