Transcript DHCP Dynamic Host Configuration

DHCP Dynamic
Host Configuration
Part 7 NVCC Professional
Development TCP/IP
DHCP Dynamic Host
Configuration Protocol
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DHCP works by providing a process for a server to
allocate IP information to clients.
Clients lease the information from the server for an
administratively defined period. When the lease expires,
the client asks for an address again, typically is
reassigned the same address.
Administrators set up DHCP servers to assign addresses
from predefined pools. DHCP servers can also offer
other information, such as DNS server addresses, WINS
server addresses, and domain names.
Major DHCP Features
•Automatic allocation – DHCP assigns a permanent IP
address to a client.
•Manual allocation – The IP address for the client is
assigned by the administrator. DHCP conveys the address to
the client.
•Dynamic allocation – DHCP assigns, or leases, an IP
address to the client for a limited period of time.
DHCP Dynamic Host Configuration
Address Pooling
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DHCP enables DHCP clients on an IP network to obtain
their configurations from a DHCP server. Less work is
involved in managing an IP network when DHCP is
used. The most significant configuration option the client
receives from the server is its IP address.
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Works in Client/Server mode
Host (DHCP Client) on a network obtain configurations from a
Server (DHCP Server)
The Server manages the configurations by answering requests
from Clients
Cannot be used for devices that need STATIC addresses i.e.
routers, switches & servers.
The Server issues LEASES
Client requests use UDP port 67, server responses use UDP
port 68.
Introducing DHCP
Client sends a broadcast
request, server receives and
notes that the Client IP
address field is empty.
Server replies with an IP
address for the Client to use.
DHCP Operation
•DHCP client broadcasts a Discover
packet on the local subnet.
•DHCP servers send an Offer packet
with lease information. (Servers may
ping an address first to ensure that it is
not already in use.)
•DHCP client selects lease and
broadcasts a Request packet.
•Selected DHCP server sends ACK
packet.
DHCP Relay and Helper Addresses
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DHCP clients broadcast their requests. Routers do not forward
broadcasts. If no DHCP server is on the client segment, DHCP
cannot happen. Helper addresses configured on the router allow the
router to send the request to a specified DHCP server on another
segment.
DHCP
Relay with
Helper
Addresses
By default, the ip helperaddress command forwards
the following eight UDP
services:
• Time
• TACACS
• DNS
• BOOTP/DHCP Server
• BOOTP/DHCP Client
• TFTP
• NetBIOS Name Service
• NetBIOS datagram Service