Protocols And Standards - H3C S9500 Series Operation Manual

Operation Manual – DHCP
H3C S9500 Series Routing Switches
Figure 1-3 DHCP message format
op: Message type defined in option field. 1 = REQUEST, 2 = REPLY
htype,hlen: Hardware address type and length of a DHCP client.
hops: Number of relay agents a request message traveled.
xid: Transaction ID, a random number chosen by the client to identify an IP
address allocation.
secs: Filled in by the client, the number of seconds elapsed since the client began
address acquisition or renewal process. Currently this field is reserved and set to
0.
flags: The leftmost bit is defined as the BROADCAST (B) flag. If this flag is set to 0,
the DHCP server sent a reply back by unicast; if this flag is set to 1, the DHCP
server sent a reply back by broadcast. The remaining bits of the flags field are
reserved for future use.
ciaddr: Client IP address.
yiaddr: 'your' (client) IP address, assigned by the server.
siaddr: Server IP address, from which the clients obtained configuration
parameters.
giaddr: The first relay agent IP address a request message traveled.
chaddr: Client hardware address.
sname: The server host name, from which the client obtained configuration
parameters.
file: Bootfile name and routing information, defined by the server to the client.
options: Optional parameters field that is variable in length, which includes the
message type, lease, DNS IP address, WINS IP address and so forth.

1.4 Protocols and Standards

RFC 2131: Dynamic Host Configuration Protocol
RFC 2132: DHCP Options and BOOTP Vendor Extensions
1-4
Chapter 1 DHCP Overview