To make clear that the total communications facility may consist of multiple networks, the constituent networks are usually referred to as subnetworks. This protocol enables the host to send data across the subnetwork to another host or, if the target host is on another subnetwork, to a router that will forward the data. IP is implemented in all of the end systems and the routers. It acts as a relay to move a block of data from one host, through one or more routers, to another host.
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UDP enables a procedure to send messages to other procedures with a minimum of protocol mechanism : for example, SNMP (Simple Network Management Protocol).
IP and IPv6
For decades, the keystone of the TCP/IP protocol architecture has been IP.
The header, together with the segment from the transport layer, forms an IP-level PDU referred to as an IP datagram or an IP packet.The header includes 32-bit source and destination addresses.