Question

I just read about DNS protocol, and found, that the name field can be writen in two ways:

1. lenght of the next label the label lenght of the next label the label … zero-byte
2. pointer to the previous name field

Next is the original article fragment:

The Resource Record Name field is encoded in the same way as the
Question Name field unless the name is already present elsewhere in
the DNS message, in which case a 2-byte field is used in place of a
length-value encoded name and acts as a pointer to the name that is
already present.

So, my question is, how can I determine the first or the second way is using in a package?

Answer 1

The first two bits are ones. This allows a pointer to be distinguished
from a label, since the label must begin with two zero bits because
labels are restricted to 63 octets or less.

See the chapter “4.1.4. Message compression” in RFC 1035