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RFC 791 describes the procedure for IP fragmentation, and transmission and reassembly of IP packets. [1] RFC 815 describes a simplified reassembly algorithm. [2] The Identification field along with the foreign and local internet address and the protocol ID, and Fragment offset field along with Don't Fragment and More Fragments flags in the IP header are used for fragmentation and reassembly of ...
This is a list of the IP protocol numbers found in the field Protocol of the IPv4 header and the Next Header field of the IPv6 header. It is an identifier for the encapsulated protocol and determines the layout of the data that immediately follows the header. Both fields are eight bits wide.
When fragmentation is performed, each IP fragment needs to carry information about which part of the original IP packet it contains. This information is kept in the Fragment Offset field, in the IP header. The field is 13 bits long, and contains the offset of the data in the current IP fragment, in the original IP packet.
In any case, the last header of the per-fragment part has its Next Header value set to 44 to indicate that a Fragment extension header follows. Each Fragment extension header has its M flag set to 1 (indicating more fragments follow), except the last, whose flag is set to 0. Each fragment's length is a multiple of 8 octets, except, potentially ...
This field is the length of the encapsulated IP packet (including Outer IP Header, Inner IP Header, IP Payload). Identification: 16 bits This field is used to identify the fragments of a datagram which will be helpful while reassembling the datagram as the encapsulator might fragment the datagram. For the Outer IP Header, a new number is generated.
If the packet size is bigger than the MTU, and the Do not Fragment (DF) bit in the packet's header is set to 0, then the router may fragment the packet. The router divides the packet into fragments. The maximum size of each fragment is the outgoing MTU minus the IP header size (20 bytes minimum; 60 bytes maximum).
An IP header is at least 20 bytes long, so the maximum value for "Fragment Offset" is restricted to 8189, which leaves room for 3 bytes in the last fragment. Because an IP internet can be connectionless, fragments from one packet may be interleaved with those from another at the destination.
This is when the Fragment ID field becomes important. It is a short-term identification of the payload frame. It is a short-term identification of the payload frame. Whenever the encapsulator needs to move on to the next payload frame, without having finished transmitting the previous one, it uses the next available Fragment ID.