Dhcp Packet Processing Modes; Protocol Specification - Huawei Quidway S3900 Series Operation Manual

Operation Manual - DHCP
Quidway S3900 Series Ethernet Switches-Release 1510
flags: The first bit is the broadcast response flag bit. It is used to identify that the
DHCP response packet is sent in the unicast or broadcast mode. 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 that the DHCP client passes after it sent
the request packet.
chaddr: Hardware address of the DHCP client.
sname: Name of the DHCP server.
file: Name of the start configuration file that the DHCP server specifies for the
DHCP client.
option: Optional variable-length fields, including packet type, valid lease time, IP
address of a DNS server, and IP address of the WINS server.

1.4 DHCP Packet Processing Modes

After the DHCP server is enabled on a device, the device processes the DHCP packet
received from a DHCP client in one of the following three modes depending on your
configuration:
Global address pool: In response to the DHCP packets received from DHCP
clients, the DHCP server picks IP addresses from its global address pools and
assigns them to the DHCP clients.
Interface address pool: In response to the DHCP packets received from DHCP
clients, the DHCP server picks IP addresses from the interface address pools and
assigns them to the DHCP clients. If there is no available IP address in the
interface address pools, the DHCP server picks IP addresses from its global
address pool that contains the interface address pool segment and assigns them
to the DHCP clients.
Trunk: DHCP packets received from DHCP clients are forwarded to an external
DHCP server, which assigns IP addresses to the DHCP clients.
You can specify the mode to process DHCP packets. For the configuration of the first
two modes, see Chapter 1 DHCP Server Configuration. For the configuration of the
trunk mode, see Chapter 3 DHCP Relay Configuration.
One interface only corresponds to one mode. In this case, the new configuration
overwrites the previous one.

1.5 Protocol Specification

Protocol specifications related to DHCP include:
RFC2131: Dynamic Host Configuration Protocol
RFC2132: DHCP Options and BOOTP Vendor Extensions
Huawei Technologies Proprietary
1-4
Chapter 1 DHCP Overview