References/pointers in messages

[treiher]

References or pointers can be used to refer to other parts of the message. The message compression mechanism of DNS is using pointers to prevent the repetition of domain names.

The OFFSET field specifies an offset from the start of the message (i.e., the first octet of the ID field in the domain header). A zero offset specifies the first byte of the ID field, etc.

It should be ensured that pointers can only point to valid positions of the message. In case of DNS a pointer should be only accepted, if it points to a beginning of a label.