Dell PowerEdge FX2/FX2s - Manual (Page 59)

5
Dynamic Host Configuration Protocol
(DHCP)
The Aggregator is auto-configured to operate as a DHCP client. The DHCP server, DHCP relay agent, and
secure DHCP features are not supported.The dynamic host configuration protocol (DHCP) is an
application layer protocol that dynamically assigns IP addresses and other configuration parameters to
network end-stations (hosts) based on configuration policies determined by network administrators.
DHCP relieves network administrators of manually configuring hosts, which can be a tedious and error-
prone process when hosts often join, leave, and change locations on the network and it reclaims IP
addresses that are no longer in use to prevent address exhaustion.
DHCP is based on a client-server model. A host discovers the DHCP server and requests an IP address,
and the server either leases or permanently assigns one. There are three types of devices that are involved
in DHCP negotiation:
DHCP Server This is a network device offering configuration parameters to the client.
DHCP Client This is a network device requesting configuration parameters from the server.
Relay Agent This is an intermediary network device that passes DHCP messages between the
client and server when the server is not on the same subnet as the host.
NOTE: The DHCP server and relay agent features are not supported on an Aggregator.
Assigning an IP Address using DHCP
The following section describes DHCP and the client in a network.
When a client joins a network:
1. The client initially broadcasts a DHCPDISCOVER message on the subnet to discover available DHCP
servers. This message includes the parameters that the client requires and might include suggested
values for those parameters.
2. Servers unicast or broadcast a DHCPOFFER message in response to the DHCPDISCOVER that offers
to the client values for the requested parameters. Multiple servers might respond to a single
DHCPDISCOVER; the client might wait a period of time and then act on the most preferred offer.
3. The client broadcasts a DHCPREQUEST message in response to the offer, requesting the offered
values.
4. After receiving a DHCPREQUEST, the server binds the clients’ unique identifier (the hardware address
plus IP address) to the accepted configuration parameters and stores the data in a database called a
binding table. The server then broadcasts a DHCPACK message, which signals to the client that it
may begin using the assigned parameters.
There are additional messages that are used in case the DHCP negotiation deviates from the process
previously described and shown in the illustration below.
Dynamic Host Configuration Protocol (DHCP) 59