The datagram length field in an IP header is 16 bits in length. Therefore, the maximum datagram size an IP datagram can support is 2^16 - 1 = 65,535 bytes
data, and header
Total number of bytes in the datagram, including the header.The length of an IP datagram itself is technically measured in bytes. The length field represents the size of both the header and the data portions of the datagram.
Source and destination IP address
maximum size is 512 bytes without header
20 bytes, without options
4th longword (bytes 13-16)
An HTML end tag example the end tag to the <header> would be: </header>
To match the packet to the process that sent it.
Data is transmitted on a network in pieces called packets, datagrams, or frames. Specifically, the frame is the header and trailer surrounding the data. The entire header, trailer, and data is called the packet or datagram. A token is a small packet used on Token Ring or FDDI networks. The token is passed from node to node to indicate to the node that data can be sent on the network.
UDP, or User Datagram Protocol is a very simple communication protocol. It is a part of the Transport Layer of the OSI model - the same as the well known TCP. UDP is very straight forward, containing very few features. There is no hand shaking, no security, no ordering of packets and very little error detection (if any at all). The structure of a UDP packet is as follows: Bits 0-15: Source Port Number (optional - leave as all zeros if unused) Bits 16-31: Destination Port Number Bits 32-47: The length of the entire UDP datagram (note that the maximum size is 2^16-1) Bits 48-63: The checksum (optional under IPv4 - leave as all zeros if unused) Bits 64-??: The actual data. About the checksum: this is the confusing part about UDP. When a checksum is computed, the UDP software creates a fake header to include in the checksum calculation - but this fake header is not actually transmitted. The structure of this fake header (officially called the "pseudo header") is: For IPv4: Bits 0-31: Source IP address (taken from the IP header) Bits 32-63: Destination IP address (taken from the IP header) Bits 64-71: Reserved - leave as all zeros Bits 72-79: Protocol (taken from the IP header) Bits 80-95: Length (taken from the UDP datagram) Bits 96-??: The UDP datagram described above. For IPv6: Bits 0-127: Source IP address Bits 128-255: Destination IP Address Bits 256-287: Length Bits 288-311: Reserved (leave as all zeros) Bits 312-319: Next header Bits 320-???: The UDP datagram described above NOTES: -this is only the structure of the UDP packet - and does not include the IP header. -Since it is possible for the checksum to end up as 0, the standard dictates that a checksum of zero be changed to 0xFFFF in order not to confuse with a checksum field which is disabled. This is true even under IPv6, where the checksum MUST be used. A checksum field value of zero is an error and the datagram should be discarded. -UDP makes no guarantees that the datagram will arrive, nor does it make any guarantees about the order that the datagram arrives in. If the user wants these features, then these will need to be implemented by the applications using UDP to communicate, or use a different communication protocol such as TCP.
IP datagram can be used to describe a portion of IP data. Each IP datagram has set of fields arranged in an order. The order is specific which helps to decode and read the stream easily. IP datagram has fields like Version, header length, Type of service, Total length, checksum, flag, protocol, Time to live, Identification, source and destination ip address, padding, options and payload. MTU:- Maximum Transmission Unit is the size of the largest packet that a communication protocol can pass. The size can be fixed by some standard or decided at the time of connection Fragmentation is a process of breaking the IP packets into smaller pieces. Fragmentation is needed when the datagram is larger than the MTU. Each fragment becomes a datagram in itself and transmitted independently from source. When received by destination they are reassembled.