TCP/IP - Computer Busses - page 356

Name: swallow.doc.ic.ac.uk
Address: 193.63.255.4
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23.10 Bootp protocol

The bootp protocol allocates IP addresses to computers based on a table of network card
MAC addresses. When a computer is first booted, the bootp server interrogates its MAC ad-
dress and then looks up the bootp table for its entry. It then grants the corresponding IP ad-
dress to the computer. The computer then uses it for connections.
23.10.1 Bootp program

The bootp program is typically run on a Linux-based PC with the bootp program. The fol-
lowing shows that the bootp program is currently running on a computer:

$ ps -ax

PID TTY STAT TIME COMMAND
1 con S 0:06 init
31 con S 0:01 /usr/sbin/inetd
14142 con S 0:00 bootpd -d 1
35 con S 0:00 /usr/sbin/lpd
49 p 3 S 0:00 /sbin/agetty 38400 tty3
14155 pp0 R 0:00 ps -ax
10762 con S 0:18 /usr/sbin/named -b /usr/local/adm/named/named.boot

For the bootp system to operate then a table is required that reconciles the MAC addresses of
the card to an IP address. In the previous example this table is contained in the bootptab file
which is located in the /etc directory. The following file gives an example bootptab :

Contents of bootptab file
# /etc/bootptab: database for bootp server
# Blank lines and lines beginning with '#' are ignored.
# Legend:
#

first field -- hostname

# (may be full domain name and probably should be)

# hd -- home directory

# bf -- bootfile

# cs -- cookie servers

# ds -- domain name servers

# gw -- gateways

# ha -- hardware address

# ht -- hardware type

# im -- impress servers

# ip -- host IP address

# lg -- log servers

# lp -- LPR servers

# ns -- IEN-116 name servers

# rl -- resource location protocol servers

# sm -- subnet mask

# tc -- template host (points to similar host entry)

# to -- time offset (seconds)

# ts -- time servers