Option Number and Description
Clients use this option to tell the server which parameters it requires. It is a series of
octets where each octet is DHCP option code.
Renewal Time Option 58
Specifies the amount of time after the IP address is granted that the client attempts to
renew its lease with the original server.
Rebinding Time Option 59
Specifies the amount of time after the IP address is granted that the client attempts to
renew its lease with any server, if the original server does not respond.
Vendor Class
Identifer
Option 60
Identifiers a user-defined string used by the Relay Agent to forward DHCP client
packets to a specific server.
L2 DHCP
Snooping
Option 82
Specifies IP addresses for DHCP messages received from the client that are to be
monitored to build a DHCP snooping database.
User Port Stacking Option 230
Set the stacking option variable to provide DHCP server stack-port detail when the
DHCP offer is set.
End Option 255
Signals the last option in the DHCP packet.
Assign 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.
5 When the client leaves the network, or the lease time expires, returns its IP address to the server in a
DHCPRELEASE message.
Dynamic Host Configuration Protocol (DHCP) 345
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