Berechnung der UDP, IP und Ethernet-Checksum

Ich wollte nur fragen wie man die Checksummen von UDP, IP und Ethernet 
berechnet. Zu Ethernet hab ich gar nichts gefunden und zu UDP und IP hab 
ich folgendes gefunden, versteh es aber nicht.

IP
The checksum field is the 16 bit one's complement of the one's
complement sum of all 16 bit words in the header and text.  If a
segment contains an odd number of header and text octets to be
checksummed, the last octet is padded on the right with zeros to
form a 16 bit word for checksum purposes.  The pad is not
transmitted as part of the segment.  While computing the checksum, the 
checksum field itself is replaced with zeros.

UDP
Checksum is the 16-bit one's complement of the one's complement sum of a
pseudo header of information from the IP header, the UDP header, and the
data,  padded  with zero octets  at the end (if  necessary)  to  make  a
multiple of two octets.