[
	endianess("be"),
	default_int_size(4),
	default_integer_value(0),
	default_bit_value(0),
	default_byte_value(0)
]
protocol ipv4 {

	[size_bits(3)] enum ePrecedence {
		NetworkControl = 0b111,
		InternetworkControl = 0b110,
		CRITIC_ECP = 0b101,
		FlashOverride = 0b100,
		Flash = 0b011,
		Immediate = 0b010,
		Priority = 0b001,
		Routine = 0b000
	};

	struct type_of_service {
		[default_value(ePrecedence.Routine)]		enum ePrecedence precedence;
		bit delay;
		bit throughput;
		bit relibility;
		
	};
	
	struct flags {
		[const(0)]		bit reserverd;
		bit df;
		bit mf;
		
	};
	
	enum eProtocols {
		Reserved=0,
		ICMP=1,
		Unassigned=2,
		Gateway_to_Gateway=3,
		CMCC=4,
		ST=5,
		TCP=6,
		UCL=7,
		Secure=9,
		BBN=10,
		NVP=11,
		PUP=12,
		Pluribus=13,
		Telenet=14,
		XNET=15,
		Chaos=16,
		User=17,
		Multiplexing=18,
		DCN=19,
		TAC=20,
		any=63,
		SATNET=64,
		MIT=65,
		SATNET=69,
		Unassigned=70,
		Internet=71,
		Backroom=76,
		WIDEBAND=78,
		WIDEBAND=79,
		Reserved=255
	};
	
	[size_bits(2)] enum eClass {
			Control=0,
			Reserved1=1,
			DebuggingAndMeasurement=2,
			Reserved2=3
	};
	
	struct ip_opt_type {
		bit copied;
		enum eClass class;
		[size_bits(5)] unsigned int number;
	};
	
	struct ip_opt {
		struct ip_opt_type type;
		union <type> {
			{copied = 0, class = eClass.Control, number = 0}:
				[size(0)]	int nodata;
			{copied = 0, class = eClass.Control, number = 1}:
				[size(0)]	int nodata;
			default:
				[size(1)]	unsigned int length;
							byte data[length-2];
		} data;
		struct ip_opt next_ip_opt;
	};
	
	struct ipv4_header {
		[size_bits(4), const(4)]	unsigned int ip_v;
		[size_bits(4), min(5)]		unsigned int ip_hl;
									struct type_of_service ip_tos;
		[size(2), min(576)]			unsigned int ip_len;
		[size(2)] 					unsigned int ip_id;
									struct flags ip_flags;
		[size_bits(13)]				unsigned int ip_off;
		[size(1), default_value(255)] 	unsigned int ip_ttl;
		[default_value(eProtocols.ICMP)]	enum eProtocols ip_p;
		[size(2)] 					unsigned int ip_sum;
		[size(4)] 					unsigned int ip_src;
		[size(4)] 					unsigned int ip_dst;
		[size(ip_hl*4 - 20)]		struct ip_opt ip_opts;
	};
	
	packet ipv4_datagram {
		struct ipv4_header hdr;
		[align(4)] byte data[hdr.ip_len - hdr.ip_hl*4];
	};
	
}