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DHCP Dynamic Host Configuration Protocol

DHCP Dynamic Host Configuration Protocol. Objectives. Describe the DHCP lease and renewal process Understand and describe the purpose of a DHCP relay Install DHCP Configure DHCP scopes, superscopes, reservations, vendor classes, and user classes Manage and monitor DHCP Troubleshoot DHCP

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DHCP Dynamic Host Configuration Protocol

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  1. DHCP • Dynamic Host Configuration Protocol

  2. Objectives • Describe the DHCP lease and renewal process • Understand and describe the purpose of a DHCP relay • Install DHCP • Configure DHCP scopes, superscopes, reservations, vendor classes, and user classes • Manage and monitor DHCP • Troubleshoot DHCP • Install and configure a DHCP relay

  3. The DHCP Process • Used 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

  4. Windows XP TCP/IP Properties

  5. Leasing an IP Address • Process to lease an address is composed of four packets • DHCPDISCOVER: 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

  6. The Four Packets in the DHCP Lease Process

  7. Renewing an IP Address • An IP address leased using DHCP can be either permanent or timed • Permanent address • DHCP server never reuses the address for another client • Timed 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 usedto force the release of a DHCP address

  8. The DHCP Lease Renewal Process

  9. DHCP Relay • DHCP packets • Are broadcast packets during the leasing process • Cannot travel across a router • DHCP relay • Receives 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

  10. Installing DHCP

  11. Authorization • Control over DHCP is very important • An unauthorized DHCP server can quickly hand out incorrect IP addressing information to hundreds of client computers • To exercise control over DHCP • Windows Server 2003 must be authorized to start DHCP Service • Authorization of a DHCP server takes place in Active Directory

  12. Authorization (Continued) • To authorize DHCP server • Must be a member of Enterprise Admins group or • Member of Enterprise Admins group must delegate permissions to you

  13. Unauthorized DHCP server error in Event Viewer

  14. The DHCP Management Snap-In

  15. Authorized DHCP server information in Event Viewer

  16. Configuring DHCP • Normally accomplished with the DHCP management snap-in • NETSH • Command used to configure DHCP • Used in larger organizations where there is a need to make changes programmatically using batch files

  17. Configuring DHCP (Continued) • DHCP elements that can be configured include • Scopes • Superscopes • Multicast scopes • Reservations • Vendor and user classes • Scope, server, and reservation options

  18. Scopes • Used to define a range of IP addresses for the DHCP server to hand out to client computers • Each scope is configured with • Name • Description • Starting IP address • Ending IP address • Subnet mask • Exclusions • Lease duration

  19. Scopes (Continued) • Name and description • Appears in the DHCP management snap-in • Starting 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 addresses • Configure 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

  20. Scopes (Continued) • Exclusions • Used to prevent some IP addresses in a scope from being handed out dynamically • Lease duration • Defines how long client computers are allowed to use an IP address • Default lease duration used by Windows Server 2003 is eight days • DHCP server • Does not begin using a scope immediately after creation • Scope must be activated before DHCP Service can begin using the scope

  21. Scope Settings

  22. Superscopes • Used to combine multiple scopes into a single logical scope • Used when a single physical part of the network has two subnets

  23. A Superscope Containing Two Scopes

  24. Multicast Scopes • Used to deliver multicast addresses to applications that require it • Time To Live (TTL) • Defines the number of routers through which a multicast packet can move • Exclusions • Define addresses between the start and end IP addresses that are not handed out • Lease duration • The length of time that an application can use a multicast address • Default lease length is 30 days

  25. Reservations • Used 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

  26. Creating a Reservation

  27. Configuring Options • DHCP can hand out the following IP configuration options • Default gateway • DNS server • WINS server • DNS is often configured at the server level

  28. Summary • DHCP • Dynamically assigns IP addresses • Can assign multicast IP addresses • DHCP lease process • Composed 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

  29. Summary (Continued) • Renewing lease • Clients attempt to renew at 50%, 87.5%, and 100% of lease time • Commands ipconfig /release and ipconfig /renew • Can release and renew DHCP leases • DHCP server • Must be authorized in Active Directory to lease addresses • Must be member of Enterprise Admins to authorize DHCP

  30. Summary (Continued) • Scope • Defines range of IP addresses that are leased to clients • Must be activated before DHCP server leases addresses in the scope • Superscope • Combines two scopes into single scope • Exclusion in scope • Used to stop a DHCP server from handing out specific addresses or range of addresses within a scope

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