any datagram that it can interpret (e.g., not object to technical errors where the meaning is still clear).
The basic internet service is datagram oriented and provides for the fragmentation of datagrams at gateways, with reassembly taking place at the destination internet protocol module in the destination host. Of course, fragmentation and reassembly of datagrams within a network or by private agreement between the gateways of a network is also allowed since this is transparent to the internet protocols and the higher-level protocols. This transparent type of fragmentation and reassembly is termed "network-dependent" (or intranet) fragmentation and is not discussed further here.
Internet addresses distinguish sources and destinations to the host level and provide a protocol field as well. It is assumed that each protocol will provide for whatever multiplexing is necessary within a host.
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September 1981 Internet Protocol Specification
Addressing
To provide for flexibility in assigning address to networks and allow for the large number of small to intermediate sized networks the interpretation of the address field is coded to specify a small number of networks with a large number of host, a moderate number of networks with a moderate number of hosts, and a large number of networks with a small number of hosts. In addition there is an escape code for extended addressing mode.
Address Formats:
High Order Bits Format Class --------------- ------------------------------- ----- 0 7 bits of net, 24 bits of host a 10 14 bits of net, 16 bits of host b 110 21 bits of net, 8 bits of host c 111 escape to extended addressing mode
A value of zero in the network field means this network. This is only used in certain ICMP messages. The extended addressing mode is undefined. Both of these features are reserved for future use.
The actual values assigned for network addresses is given in "Assigned Numbers" [9].
The local address, assigned by the local network, must allow for a single physical host to act as several distinct internet hosts. That is, there must be a mapping between internet host addresses and network/host interfaces that allows several internet addresses to correspond to one interface. It must also be allowed for a host to have several physical interfaces and to treat the datagrams from several of them as if they were all addressed to a single host.
Address mappings between internet addresses and addresses for ARPANET, SATNET, PRNET, and other networks are described in "Address Mappings" [5].
Fragmentation and Reassembly.
The internet identification field (ID) is used together with the source and destination address, and the protocol fields, to identify datagram fragments for reassembly.
The More Fragments flag bit (MF) is set if the datagram is not the
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