Post on 19-Jan-2016
description
DHCP Dynamic Host Configuration Protocol
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ObjectivesDescribe the DHCP lease and renewal
processUnderstand and describe the purpose of a
DHCP relayInstall DHCPConfigure DHCP scopes, superscopes,
reservations, vendor classes, and user classesManage and monitor DHCPTroubleshoot DHCPInstall and configure a DHCP relay
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The DHCP ProcessUsed to automatically deliver IP addressing
information to client computers on a network
Can also deliver IP address information to servers and other devices such as printers
Use of DHCP reduces time spent configuring computers on network
Client computers use DHCP by default unless static IP address is specified during installation
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Windows XP TCP/IP Properties
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Leasing an IP AddressProcess to lease an address is composed of four packetsDHCPDISCOVER: sent from the client
computer to the broadcast IP address 255.255.255.255
DHCPOFFER: response sent after receiving DHCPDISCOVER packet
DHCPREQUEST: response of DHCP client after receiving DHCPOFFER packet
DHCPACK: response sent by chosen DHCP server indicating confirmation that lease has been chosen and client can now use the lease
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The Four Packets in the DHCP Lease Process
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Renewing an IP AddressAn IP address leased using DHCP can be either permanent or timed
Permanent addressDHCP server never reuses the address for
another clientTimed lease
Allows clients to use an IP address for a specified period of time
Windows clients attempt to renew their lease after 50% of lease time has expired
ipconfig /release command is used to force the release of a DHCP address
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The DHCP Lease Renewal Process
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DHCP RelayDHCP packetsAre broadcast packets during the leasing
processCannot travel across a router
DHCP relayReceives broadcast DHCP packets from clients
and forwards them as unicast packets to a DHCP server
Must be configured with IP address of the DHCP server to deliver unicast packets
DHCP Relay Service cannot be installed on the same server as the DHCP Service
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Installing DHCP
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AuthorizationControl over DHCP is very importantAn unauthorized DHCP server can quickly
hand out incorrect IP addressing information to hundreds of client computers
To exercise control over DHCPWindows Server 2003 must be authorized
to start DHCP Service Authorization of a DHCP server takes place
in Active Directory
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Authorization (Continued)
To authorize DHCP serverMust be a member of Enterprise Admins
group orMember of Enterprise Admins group must
delegate permissions to you
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Unauthorized DHCP server error in Event Viewer
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The DHCP Management Snap-In
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Authorized DHCP server information in Event Viewer
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Configuring DHCPNormally accomplished with the DHCP
management snap-inNETSH
Command used to configure DHCPUsed in larger organizations where there is
a need to make changes programmatically using batch files
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Configuring DHCP (Continued)DHCP elements that can be configured
includeScopesSuperscopesMulticast scopesReservationsVendor and user classesScope, server, and reservation options
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ScopesUsed to define a range of IP addresses for the DHCP server to hand out to client computers
Each scope is configured withNameDescriptionStarting IP addressEnding IP addressSubnet maskExclusionsLease duration
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Scopes (Continued)Name and description
Appears in the DHCP management snap-inStarting and ending IP addresses
Define range of IP addresses that can be handed out by the DHCP server
Strategies when defining starting and ending IP addressesConfigure scope to use all available
addresses on a subnet, then exclude the static IP addresses being used by hosts
Configure scope to use addresses that are not already in use
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Scopes (Continued)Exclusions
Used to prevent some IP addresses in a scope from being handed out dynamically
Lease durationDefines how long client computers are
allowed to use an IP addressDefault lease duration used by Windows
Server 2003 is eight daysDHCP server
Does not begin using a scope immediately after creation
Scope must be activated before DHCP Service can begin using the scope
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Scope Settings
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Superscopes
Used to combine multiple scopes into a single logical scope
Used when a single physical part of the network has two subnets
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A Superscope Containing Two Scopes
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Multicast ScopesUsed to deliver multicast addresses to
applications that require itTime To Live (TTL)
Defines the number of routers through which a multicast packet can move
ExclusionsDefine addresses between the start and
end IP addresses that are not handed outLease duration
The length of time that an application can use a multicast address
Default lease length is 30 days
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ReservationsUsed to hand out a specific IP address to a particular client computer or device on the network
Can also be beneficial when firewalls are in place
Created based on the MAC address of the network card
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Creating a Reservation
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Configuring OptionsDHCP can hand out the following IP
configuration optionsDefault gatewayDNS serverWINS server
DNS is often configured at the server level
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SummaryDHCP
Dynamically assigns IP addressesCan assign multicast IP addresses
DHCP lease processComposed of DHCPDISCOVER,
DHCPOFFER, DHCPREQUEST, and DHCPACK
DHCPNAK: used by DHCP servers to decline renewal of lease
DHCPRELEASE: used by clients to inform DHCP server that lease is no longer required
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Summary (Continued)
Renewing leaseClients attempt to renew at 50%, 87.5%,
and 100% of lease timeCommands ipconfig /release and
ipconfig /renewCan release and renew DHCP leases
DHCP serverMust be authorized in Active Directory to
lease addressesMust be member of Enterprise Admins to
authorize DHCP
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Summary (Continued)Scope
Defines range of IP addresses that are leased to clients
Must be activated before DHCP server leases addresses in the scope
SuperscopeCombines two scopes into single scope
Exclusion in scopeUsed to stop a DHCP server from handing
out specific addresses or range of addresses within a scope
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