This section will describe the handling of datagrams received on UDP port 520. Before processing the datagrams in detail, certain general format checks must be made. These depend upon the version number field in the datagram, as follows:
|0||Datagrams whose version number is zero are to be ignored. These are from a previous version of the protocol, whose packet format was machine-specific.|
|1||Datagrams whose version number is one are to be processed as described in the rest of this specification. All fields that are described above as "must be zero" are to be checked. If any such field contains a non-zero value, the entire message is to be ignored.|
|>1||Datagrams whose version number are greater than one are to be processed as described in the rest of this specification. All fields that are described above as "must be zero" are to be ignored. Future versions of the protocol may put data into these fields. Version 1 implementations are to ignore this extra data and process only the fields specified in this document.|
After checking the version number and doing any other preliminary checks, processing will depend upon the value in the command field.