OS10 Enterprise Edition User Guide Release 10.4.0E(R3)

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Packet format and options

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

The configuration parameters are options in the DHCP packet in type, length, value (TLV) format. To limit the number of parameters that servers must 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.

dhcp packet format

The table shows common options using DHCP packet formats.

Subnet mask
1 — Client’s subnet mask
Router
3 — Router IP addresses that serve as the client’s default gateway
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 can use 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 — Parameters the server requires for DHCP clients. 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
User port stacking
230 — Stacking option variable to provide DHCP server stack-port details when the DHCP offer is set.
End
255 — Signal of the last option in the DHCP packet

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