Q14,paper2,june 12..Which of the following TCP/IP Internet protocol is diskless machine uses to obtain its IP address from a server ?

Options (A) RAP           (B) RIP              (C) ARP            (D) X.25

Answer © ARP.

Explanation:

A mechanism is needed to map IP-addresses onto Ethernet addresses. This is the so-called Address Resolution Protocol, or ARP. In fact, ARP is not confined to Ethernets at all, but is used on other types networks such as ham radio as well. The idea underlying ARP is exactly what most people do when they have to find Mr. X. Ample in a throng of 150-people: they go round, calling out his name, confident that he will respond if he's there.

When ARP wants to find out the Ethernet address corresponding to a given IP-address, it uses a feature of Ethernet known as ``broadcasting,'' where a datagram is addressed to all stations on the network simultaneously. The broadcast datagram sent by ARP contains a query for the IP-address. Each receiving host compares this to its own IP-address, and if it matches, returns an ARP reply to the inquiring host. The inquiring host can now extract the sender's Ethernet address from the reply.

Once a host has discovered an Ethernet address, it stores it in its ARP cache, so that it doesn't have to query for it the next time it wants to send a datagram to the host in question. However, it is unwise to keep this information forever; for instance, the remote host's Ethernet card may be replaced because of technical problems, so the ARP entry becomes invalid. To force another query for the IP-address, entries in the ARP cache are therefore discarded after some time. Sometimes, it is also necessary to find out the IP-address associated with a given Ethernet address. This happens when a diskless machine wants to boot from a server on the network, which is quite a common situation on local area networks. A disk less client, however, has virtually no information about itself-- except for its Ethernet address So what it basically does is broadcast a message containing a plea for boot servers to tell it its IP-address. When a computer that is connected to a network is powered up and  boots its operating system, the system software broadcasts BOOTP messages onto the network to request an IP address assignment. A BOOTP configuration server assigns an IP address based on the request from a pool of addresses configured by an administrator.
BOOTP is implemented using the (UDP) as transport protocol, port number 67 is used by the server to receive client requests and port number 68 is used by the client to receive server responses. BOOTP operates only on ip4networks. DHCP servers also provide the legacy BOOTP functionality.
The Reverse Address Resolution Protocol (RARP) is an obsolete computer networking protocol used by a client computer to request its IP4 address from a computer network, when all it has available is its link layeror hardware address, such as a MAC address. The client broadcasts the request, and does not need prior knowledge of the network topology or the identities of servers capable of fulfilling its request.
RARP has been rendered obsolete by the (BOOTP) and the modern  (DHCP), which both support a much greater feature set than RARP.
RARP requires one or more server hosts to maintain a database of mappings of Link Layer addresses to their respective protocol addresses.  (MAC) addresses needed to be individually configured on the servers by an administrator. RARP was limited to serving only  ip addresses .