ipv4

type IPv4 struct {
	Version        uint8 //4-bits
	IHL            uint8 //4-bits
	DSCP           uint8 //6-bits
	ECN            uint8 //2-bits
	Length         uint16
	Id             uint16
	Flags          uint16 //3-bits
	FragmentOffset uint16 //13-bits
	TTL            uint8
	Protocol       uint8
	Checksum       uint16
	NWSrc          net.IP
	NWDst          net.IP
	Options        util.Buffer
	Data           util.Message
}