Dhcp Packet Format - H3C S3100-52P Operation Manual

Operation Manual – DHCP
H3C S3100-52P Ethernet Switch

1.3 DHCP Packet Format

DHCP has eight types of packets. They have the same format, but the values of some
fields in the packets are different. The DHCP packet format is based on that of the
BOOTP packets. The following figure describes the packet format (the number in the
brackets indicates the field length, in bytes):
Figure 1-2 DHCP packet format
The fields are described as follows:
op: Operation types of DHCP packets, 1 for request packets and 2 for response
packets.
htype, hlen: Hardware address type and length of the DHCP client.
hops: Number of DHCP relay agents which a DHCP packet passes. For each
DHCP relay agent that the DHCP request packet passes, the field value increases
by 1.
xid: Random number that the client selects when it initiates a request. The number
is used to identify an address-requesting process.
secs: Elapsed time after the DHCP client initiates a DHCP request.
flags: The first bit is the broadcast response flag bit, used to identify that the DHCP
response packet is a unicast (set to 0) or broadcast (set to 1). Other bits are
reserved.
ciaddr: IP address of a DHCP client.
yiaddr: IP address that the DHCP server assigns to a client.
siaddr: IP address of the DHCP server.
giaddr: IP address of the first DHCP relay agent that the DHCP client passes after
it sent the request packet.
chaddr: Hardware address of the DHCP client.
sname: Name of the DHCP server.
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Chapter 1 DHCP Overview