HP-UX IP Address and Client Management Administrator's Guide (October 2009)

BOOTP and TFTP Overview
The Bootstrap Protocol (BOOTP) allows certain systems to discover network configuration
information (such as an IP address and a subnet mask) and boot information automatically.The
Trivial File Transfer Protocol (TFTP) is a simple protocol used to read and write files to or from
a remote system. It allows users to transfer files to and from a remote machine. You can specify
the remote host on the command line, and the TFTP server, tftp, uses the host as the default
host for future transfers. Otherwise, tftp issues a prompt and expects the user to connect to a
host. If you want to connect to a particular port, you can specify the port number as an optional
parameter. TFTP does not require user login or validation. Diskless clusters use TFTP to transfer
required files while booting.
Together, TFTP and BOOTP allow a system to provide boot information for client systems that
support BOOTP, such as HP’s 700/X terminal. These protocols are implemented on the Internet
User Datagram Protocol (UDP). Therefore, you can use these protocols across networks that
support UDP.
How BOOTP Works
The Bootstrap Protocol (BOOTP) allows a client system to discover its IP address, the address
of a BOOTP server, and the name of a file that is loaded into memory and executed.
BOOTP operates in two phases:
• Address determination and bootfile selection
• File transfer
In the first phase, the address determination and bootfile selection occur. This phase uses the
BOOTP server, bootpd. After the address and file name information is obtained, control passes
to the second phase of bootstrap, where a file transfer occurs. This phase uses the TFTP server,
tftpd.
NOTE: HP recommends that Remote Maintainance Protocol (RMP) clients upgrade to bootp
or DHCPv6 to obtain the IP address and other configuration information.
Address Determination and Bootfile Selection
The first phase of BOOTP involves a bootrequest packet that is broadcast by the BOOTP client.
A BOOTP server that receives the bootrequest sends a bootreply to the client if the BOOTP server
finds the client’s boot information in its database; otherwise, the BOOTP server relays the
bootrequest to other BOOTP servers if it finds relay information for the client in its database.
The steps performed by the BOOTP server and the client in the process of address determination
and bootfile selection are as follows:
1. The BOOTP client broadcasts a bootrequest on the network. Before sending the bootrequest,
the client does the following:
• It sets the hops field of the bootrequest packet to 0. Each time a BOOTP server relays
the client’s bootrequest, the hops field is incremented by 1. If the hops value exceeds
the maximum hop value configured for this client on a BOOTP server, the bootrequest
is dropped. The hops value limits the number of times a bootrequest can be relayed.
• It sets the secs field of the bootrequest packet to 0 for a first-time request. If the client
does not receive a reply to this request, it sets the value of this field to the number of
seconds since the first request was sent. If the value of the secs field is less than the
threshold value configured for this client on a BOOTP server, the bootrequest is dropped.
44 Overview