Transcript document

RFC 2131
DHCP
Dynamic
Host
Configuration
Protocol
Definitions
 DHCP Client – an Internet host using DHCP to
obtain Configuration parameters
 DHCP Server – an Internet host that returns
configurations parameters to DHCP clients
 BOOTP relay agent – an Internet host or router that
passes DHCP messages between DHCP clients and
DHCP servers
 Binding – a collection of configuration parameters,
including at least an IP address
Abstract
The Dynamic Host Configuration Protocol
provides a framework for passing configuration
information to hosts on a TCP/IP network. DHCP
is based on the Bootstrap Protocol, adding the
capability of automatic allocation of reusable
network addresses and additional configuration
options. DHCP captures the behavior of BOOTP
relay agents and DHCP participants can
interoperate with BOOTP participants
DHCP Design Goals
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Clients should require no manual configuration
Networks should require no manual
configuration for individual clients
DHCP should not require a server on each subnet
A DHCP client must be prepared to receive
multiple responses to a request for configuration
parameters
DHCP must coexist with statically configured
hosts
Design goals specific to the
transmission of network layer
parameters
 Guarantee that any specific network address will
not be in use by more than one DHCP client at a
time
 Retain DHCP client configuration across DHCP
client reboot
 Retain DHCP client configuration across server
reboots
 Allow automated assignment of configuration
parameters to new clients
 Support fixed of permanent allocation of
configuration parameters to specific clients
WARNING!
A host should not act as a DHCP server
unless explicitly configured to do so by
a system administrator.
DHCP supports three mechanisms
for IP address allocation.
 Automatic Allocation – DHCP assigns a permanent
IP address to a client
 Manual Allocation – a clients IP address is assigned
by the network administrator, and DHCP is used to
simply convey the assigned address to the client
 Dynamic Allocation – DHCP assigns and IP address
to a client for a limited period of time
DHCP Packet
DHCP message type
(option 53)
 DHCPDISCOVER
 DHCPOFFER
 DHCPREQUEST
 DHCPDECLINE
 DHCPACK
 DHCPNAK
 DHCPRELEASE
DHCP consists of two
components:
•Storage of network parameters for
network clients
•A mechanism for allocation of
network addresses to hosts.
Provide persistent storage of
network parameters
The first service provided by DHCP is
to provide persistent storage of network
parameters for network clients.
Key value pairs
The DHCP service stores a key-value entry
for each client where the key is some unique
identifier and the value contains the
configuration parameters for the client.
Example key. IP-subnet-number, hardware
address
Dynamic allocation of network
addresses
The second service provided by DHCP
is the allocation of temporary or
permanent network addresses to
clients.