Dell Configuration Guide for the S4048–ON System 9.14.2.5

The server listens on port 67 and transmits to port 68; the client listens on port 68 and transmits to port 67. The configuration parameters are carried as options in the DHCP packet in Type, Length, Value (TLV) format; many options are specified in RFC 2132. To limit the number of parameters that servers must provide, hosts specify the parameters that they require, and the server sends only those parameters. Some common options are shown in the following illustration.

The following table lists common DHCP options.

Option

Number and Description

Subnet Mask

Option 1

Specifies the client’s subnet mask.

Router

Option 3

Specifies the router IP addresses that may serve as the client’s default gateway.

Domain Name Server

Option 6

Specifies the domain name servers (DNSs) that are available to the client.

Domain Name

Option 15

Specifies the domain name that clients should use when resolving hostnames via DNS.

IP Address Lease Time

Option 51

Specifies the amount of time that the client is allowed to use an assigned IP address.

DHCP Message Type

Option 53

• 1: DHCPDISCOVER
• 2: DHCPOFFER
• 3: DHCPREQUEST
• 4: DHCPDECLINE
• 5: DHCPACK
• 6: DHCPNACK
• 7: DHCPRELEASE
• 8: DHCPINFORM

Parameter Request List

Option 55

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

Identifies 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.