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After designing a scalable IP addressing
scheme for the enterprise, you will be faced with
the daunting task of implementation. Routers, servers, and other key nodes
usually
require special attention from administrators, but desktop clients are
often automatically
assigned IP configurations using Dynamic Host Configuration Protocol (DHCP).
Because desktop clients typically make up the bulk of network nodes, DHCP is good
news for
systems administrators. Small offices and home offices can also take
advantage of DHCP
by using Easy IP, a Cisco IOS feature set that combines DHCP with NAT
functions.
DHCP works by configuring servers to give out IP configuration information
to clients.
Clients lease the information from the server for an administratively
defined period. When the lease is up, the host must ask for another address,
although the host is
typically reassigned the same one.
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Administrators typically prefer to use a Microsoft NT server or a UNIX
computer to offer
DHCP services because these solutions are highly scalable and relatively
easy to manage. Even so, the Cisco IOS offers an optional, fully featured DHCP
server, which
leases configurations for 24 hours by default.
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. Most DHCP servers also allow you to define
specifically
what client MAC addresses can be serviced and to automatically assign the
same number to a particular host each time.
Note:
BootP was originally defined in RFC 951 in 1985. It is the predecessor of
DHCP, and
it shares some operational characteristics. Both protocols use UDP ports
67 and 68, which are well known as "BootP" ports because BootP came before
DHCP.
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