DHCP for Windows 2000

BOOTP Packet Structure

Before delving into the conversation between a BOOTP client and a BOOTP server, I will examine the packet structure of the BOOTP protocol (see Figure 2.2).

A BOOTP packet’s transmission order is from left to right, top to bottom—just as you are reading this page. The number shown in parentheses is the number of octets (or bytes) each field occupies.

Figure 2-2. BOOTP packet structure

Field Definitions

Table 2.1 lists the available fields in a BOOTP packet and describes the type of information each field is to supply.

Table 2-1. BOOTP Field Definitions

Field	Definition
op	Specifies the message type: if 1, the message is a BOOTPREQUEST; if 2, the message is a BOOTPREPLY.
htype	Specifies the hardware address type (i.e., Ethernet or Token Ring). 10 Mbps Ethernet = 1.
hlen	Specifies the hardware address length. Ethernet = 6.
hops	Specifies the number of hops or routers between the client and the server.
xid	Specifies the transaction ID number. This is a random number that is used to match up the request with the reply that is returned.
secs	Specifies how long it has been since the client was booted up.
flags	Specifies whether the BOOTPREPLY message should be sent as a unicast message or a broadcast message.
ciaddr	Specifies the client’s IP address if known. This is only used in a bootprequest message.
yiaddr	Specifies the IP address assigned to ...