Dell EMC SmartFabric OS10 User Guide Release 10.5.1

The DHCP server listens on port 67 and transmits to port 68. The DHCP client listens on port 68 and transmits to port 67.

In the DHCP packet format, configuration parameters are options in the DHCP packet in type, length, value (TLV) format. To limit the number of parameters that servers provide, hosts enter the parameters that they require and the server sends only those parameters. DHCP uses the User Datagram Protocol (UDP) as its transport protocol.

The following options are commonly used in DHCP packets.

DHCP Option

Description

Subnet mask

1 — Subnet mask of the client

Router

3 — Router IP addresses that serve as the default gateway for the client

Domain name server

6 — Domain name servers (DNS) that are available to the client

Domain name

15 — Domain name that clients use to resolve hostnames via DNS

IP address lease time

51 — Amount of time that the client uses an assigned IP address

DHCP message type

53:

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

Parameter request list

55 — A list of parameters that a DHCP client requires from the DHCP server. This is a series of octets where each octet is a DHCP option code

Renewal time

58 — Amount of time, after the IP address is granted, that the client attempts to renew its lease with the original server

Rebinding time

59 — 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 identifier

60 — User-defined string the Relay Agent uses to forward DHCP client packets to a specific DHCP server

DHCP relay agent information option

82 — Helps secure DHCP traffic that goes through a DHCP relay agent, and ensures that communication between the DHCP relay agent and the DHCP server is not compromised.

User port stacking

230 — Stacking option variable that provides the DHCP server stack-port details when the DHCP offer is set

End

255 — Signal of the last option in the DHCP packet