What is need of RARP? Explain working of RARP.
Answers
RARP -- Reverse Address Resolution Protocol
What is it for: Diskless clients don't have a place to store there IP number. Rarp translates machines addresses into IP numbers.
How RARP works: The client broadcasts a RARP packet with an ethernet broadcast address, and it's own physical address in the data portion. The server responds by telling the client it's IP address. Note there is no name sent. Also note there is no security. Does not use IP; uses's physical frames.
Common RARP improvements: Don't let an RARP client retry indefinitlly. That just causes wasted broadcasts. Have a backup RARP server or two, on random time delays.
Interesting Question: When should the server broadcast the answer instead of target it? What gets put in the rest of the packet (since there is a large minimum packet length?
BOOTP -- The Bootstrapping Protocol
What is it for: Diskless clients don't have a place to store there IP number. Bootp translates machines addresses into IP numbers. Because it uses IP packets, application level programmers can write bootp servers.
How BOOTP works: The client broadcasts a BOOTP packet with source and destination IP broadcast addresses (all 1's), and it's own physical address in the data portion. The server responds by telling the client it's actual IP address, and some other info (see page 368). Note that the server must also send to a broadcast address, since there is no IP-> physical address mapping in the server's ARP cache yet, and the client won't yet respond to ARP requests (since it does not yet recognize it's IP address).
The Boot file: BOOTP sends a suggested file server and file name to the client. The client can then use anbother protocol (TFTP?) to retrieve that file, and boot using the resulting image.
Vendor Specific Area: Can contain anything, but often time of day, dns server name, printer IP address, and such.
Advantages over RARP: Carries more info in the reply.