Operation Manual - DHCP
Quidway S3900 Series Ethernet Switches-Release 1510 Chapter 2 DHCP Server Configuration
Huawei Technologies Proprietary
2-2
z DHCP is an UDP-based protocol operating at the application layer. When a
DHCP server in a fabric system runs on a Layer 2 network device, DHCP packets
are directly forwarded by hardware instead of being delivered to the DHCP server,
or being redirected to the master unit by UDP HELPER. This idles the DHCP
server. DHCP packets can be redirected to the DHCP server on the master unit
by UDP HELPER only when the Layer 2 device is upgraded to a Layer 3 device.
Caution:
z When you merge two or more IRF systems into one IRF system, a new master unit
is elected, and the new IRF system adopts new configurations accordingly. This
may result in the existing system configurations (including the address pools
configured for the DHCP servers) being lost. As the new IRF system cannot inherit
the original DHCP server configurations, you need to perform DHCP server
configurations for it.
z When an IRF system is split into multiple new IRF systems, some of the new IRF
systems may be degraded to Layer 2 devices. For a new IRF system degraded to
Layer 2 device, although the original DHCP server still exists in the new system, it
run idle for being unable to receive any packets. When the IRF system restores to a
Layer 3 device due to being merged into a new IRF system, it adopts the
configurations on the new IRF system. And you need to perform DHCP server
configurations if the new IRF system does not have DHCP server-related
configurations.
z In an IRF system, the UDP HELPER function must be enabled on the DHCP
servers that are in fabric state.
2.1.3 DHCP Address Pool
A DHCP address pool holds the IP addresses to be assigned to DHCP clients. When a
DHCP server receives a DHCP request from a DHCP client, it selects an address pool
depending on the configuration, picks an IP address from the pool and sends the IP
address and other related parameters (such as the IP address of the DNS server, and
the lease time of the IP address) to the DHCP client.
I. Types of address pool
The address pools of a DHCP server fall into two types: global address pool and
interface address pool.
z A global address pool is created by executing the dhcp server ip-pool command
in system view. It is valid on the current device.
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