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15.3 We said that the TFTP sender performs the timeout and retransmission to handle lost packets. How does this
affect the use of TFTP when it's being used as part of the bootstrap process?
15.4 What is the limiting factor in the time required to transfer a file using TFTP? file:///D|/Documents%20and%20Settings/bigini/Documenti/homenet2run/tcpip/tcp-ip-illustrated/tftp_tri.htm (4 of 4) [12/09/2001 14.47.07] Chapter 16. BOOTP: Bootstrap Protocol BOOTP: Bootstrap Protocol
In Chapter 5 we described how a diskless system, with no knowledge of its IP address, can
determine its IP address using RARP when it is bootstrapped. There are two problems with
RARP: (1) the only thing returned is the IP address, and (2) since RARP uses a link-layer
broadcast, RARP requests are not forwarded by routers (necessitating an RARP server on
every physical network). This chapter describes an alternative method for a diskless system to
bootstrap itself, called the Bootstrap Protocol, or BOOTP.
BOOTP uses UDP and normally works in conjunction with TFTP (Chapter 15). RFC 951
[Croft and Gilmore 1985] is the official specification for BOOTP with clarifications given in
RFC 1542 [Wimer 1993]. 16.2 BOOTP Packet Format
BOOTP requests and replies are encapsulated in UDP datagrams, as shown in Figure 16.1. Figure 16.1 Encapsulation of BOOTP requests and replies within a UDP datagram.
Figure 16.2 shows the format of the 300-byte BOOTP request and reply. file:///D|/Documents%20and%20Settings/bigini/Documenti/homenet2run/tcpip/tcp-ip-illustrated/bootp.htm (1 of 9) [12/09/2001 14.47.08] Chapter 16. BOOTP: Bootstrap Protocol Figure 16.2 Format of BOOTP request and reply.
Opcode is 1 for a request and 2 for a reply. The hardware type field is 1 for a 10 Mbits/sec
Ethernet, the same value that is in the field of the same name in an ARP request or reply
(Figure 4.3). Similarly, the hardware address length is 6 bytes for an Ethernet.
The hop count is set to 0 by the client, but can be used...
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