70-291: MCSE Guide to Managing a Microsoft Windows Server 2003 Network Chapter 4: Dynamic Host Configuration Protocol

70-291: MCSE Guide to Managing a Microsoft Windows Server Network2 Objectives Outline the benefits of using DHCP Describe the DHCP lease and renewal process Install and authorize the DHCP service Configure DHCP scopes Create DHCP reservations for client computers Configure DHCP options Understand and describe the purpose of a DHCP relay Install and configure a DHCP relay

70-291: MCSE Guide to Managing a Microsoft Windows Server Network3 DHCP Overview Used to automatically deliver IP addressing Reduces the amount of time you spend configuring computers on your network Used by default unless you specify otherwise The ipconfig /all command will indicate whether the configuration came from a DHCP server computer

70-291: MCSE Guide to Managing a Microsoft Windows Server Network4 DHCP Overview (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network5 DHCP Overview (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network6 Leasing an IP Address An IP address is leased during the boot process The overall process is composed of four broadcast packets: DHCPDISCOVER DHCPOFFER DHCPREQUEST DHCPACK

70-291: MCSE Guide to Managing a Microsoft Windows Server Network7 Leasing an IP Address (continued) Any DHCP server that receives the DHCPDISCOVER packet responds with a DHCPOFFER packet The DHCP client responds to the DHCPOFFER packet it receives with a DHCPREQUEST packet A DHCPACK packet indicates confirmation that the client can use the lease Once DHCPACK is received, the client can start using the IP address and options in the lease

70-291: MCSE Guide to Managing a Microsoft Windows Server Network8 Leasing an IP Address (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network9 Renewing an IP Address The IP address can either be permanent or timed A permanent address is never reused for another client Timed leases expire after a certain amount of time Windows clients attempt to renew their lease after 50% of the lease time has expired A DHCP server may either honor or reject a renew request

70-291: MCSE Guide to Managing a Microsoft Windows Server Network10 Renewing an IP Address (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network11 Installing and Authorizing the DHCP Service A DHCP service must be authorized after installation

70-291: MCSE Guide to Managing a Microsoft Windows Server Network12 Installing the DHCP Service DHCP is a standard service It is included in Windows Server 2003 It is not installed as part of a default installation

70-291: MCSE Guide to Managing a Microsoft Windows Server Network13 Installing the DHCP Service (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network14 Authorizing the DHCP Service Unauthorized DHCP servers can hand out bad information DHCP will not start unless authorized If Active Directory is used, authorization takes place in Active Directory DHCP servers are automatically authorized under certain conditions

70-291: MCSE Guide to Managing a Microsoft Windows Server Network15 Authorizing the DHCP Service (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network16 Authorizing the DHCP Service (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network17 Configuring DHCP Scopes Scope defines a range of IP addresses Each scope is configured with: Description Starting IP address Ending IP address Subnet mask Exclusions Lease duration Two strategies exist for defining the starting and ending IP addresses Allow all and exempt the few static addresses Use only the addresses not already in use

70-291: MCSE Guide to Managing a Microsoft Windows Server Network18 Configuring DHCP Scopes (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network19 Configuring DHCP Scopes (continued) Exclusions are used to prevent some IP addresses from being handed out dynamically Lease duration defines how long client computers are allowed to use an IP address Default lease duration is eight days A scope must be activated before the DHCP service can begin using it

70-291: MCSE Guide to Managing a Microsoft Windows Server Network20 Superscopes Used to combine multiple scopes into a single logical scope Allows multiple scopes to be treated as a single scope If a superscope is used, then the DHCP server offers only one lease as opposed to multiple leases

70-291: MCSE Guide to Managing a Microsoft Windows Server Network21 Superscopes (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network22 Multicast Scopes Used to deliver multicast addresses to applications that require it Multicast addresses are used to deliver packets to groups of computers Start and end IP addresses define the range of addresses that can be handed out by DHCP servers TTL defines the number of routers through which a multicast packet can move

70-291: MCSE Guide to Managing a Microsoft Windows Server Network23 Multicast Scopes (continued) Exclusions define addresses that should not be handed out Lease duration defines the length of time that an application can use a multicast address Default lease length is 30 days

70-291: MCSE Guide to Managing a Microsoft Windows Server Network24 Creating DHCP Reservations Reservations are used to hand out a specific IP address to a particular client Useful when delivering IP addresses to devices that would normally use static addresses Can also be beneficial when firewalls are in place Reservations are created based on MAC addresses

70-291: MCSE Guide to Managing a Microsoft Windows Server Network25 Creating DHCP Reservations (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network26 Configuring DHCP Options DHCP can hand out a variety of other IP configuration options It is common that all workstations within an entire organization use the same DNS servers DNS is often configured at the server level

70-291: MCSE Guide to Managing a Microsoft Windows Server Network27 Configuring DHCP Options (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network28 Configuring DHCP Options (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network29 Vendor and User Classes Used to differentiate between clients within a scope Vendor classes are based on the operating system User classes are defined based on network connectivity or the administrator You can use the ipconfig /setclassid command to set the DHCP user class ID

70-291: MCSE Guide to Managing a Microsoft Windows Server Network30 Vendor and User Classes (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network31 Vendor and User Classes (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network32 Configuring a DHCP Relay DHCP packets cannot travel across a router A relay agent is necessary in order to have a single DHCP server handle all leases Relay agents receive broadcast DHCP packets and forward them as unicast packets to a DHCP server The DHCP relay cannot be installed on the same server as the DHCP service

70-291: MCSE Guide to Managing a Microsoft Windows Server Network33 Configuring a DHCP Relay (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network34 Configuring a DHCP Relay (continued)

70-291: MCSE Guide to Managing a Microsoft Windows Server Network35 Summary DHCP dynamically assigns IP address information to clients on a network The DHCP lease process is composed of four packets: DHCPDISCOVER DHCPOFFER DHCPREQUEST DHCPACK A DHCP client attempts to renew its lease at 50%, 87.5%, and 100% of the lease time The commands ipconfig /release and ipconfig /renew can be used to release and renew DHCP leases

70-291: MCSE Guide to Managing a Microsoft Windows Server Network36 Summary (continued) If the Active Directory service is present on your network, each DHCP server must be authorized in Active Directory to lease addresses to clients A scope defines a range of IP addresses that are leased to clients A superscope combines two scopes into a single logical unit to service network segments with two subnets

70-291: MCSE Guide to Managing a Microsoft Windows Server Network37 Summary (continued) An exclusion in a scope can stop a DHCP server from handing out specific addresses A reservation allows you to give a specific workstation a defined IP address by tying the DHCP lease to the MAC address of the client Vendor and user classes can be used to configure some client computers with different options, depending on the class to which they belong A DHCP relay agent is required on each network that requires IP configuration from a DHCP server across a router