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MIS 4700

MIS 4700. Dynamic Host Configuration Protocol (DHCP) Part A. Introducing DHCP. Provides a way for client computer to request an IP address DHCP delivers the necessary configuration information IP address Subnet mask IP Gateways Address for DNS servers Address for WINS servers.

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MIS 4700

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  1. MIS 4700 Dynamic Host Configuration Protocol (DHCP) Part A Guide to TCP/IP, Second Edition

  2. Introducing DHCP • Provides a way for client computer to request an IP address • DHCP delivers the necessary configuration information • IP address • Subnet mask • IP Gateways • Address for DNS servers • Address for WINS servers Guide to TCP/IP, Second Edition

  3. Introducing DHCP (cont.) • Administer client IP address assignments and configuration data from a single, centralized server • Address pool or address scope • One or more range of IP address • Exclude an address or range of address • Address lease Guide to TCP/IP, Second Edition

  4. How DHCP Works • Client perspective on DHCP • Client is configured to “Obtain an IP address automatically” • At boot-up the client broadcasts DHCP address request • DHCP servers reply offers an address lease • Client accepts address lease offer • Server offers an IP address with a lease time limit • Half the lease time the client attempts to renew lease Guide to TCP/IP, Second Edition

  5. How DHCP Works (cont.) Guide to TCP/IP, Second Edition

  6. The Role Of Leases • Length of leases vary • One to three weeks in length are typical • One to three days for networks with temps or roving workers • Four to eight hours are common on ISP networks Guide to TCP/IP, Second Edition

  7. DHCP Software Elements • Three elements to DHCP software • DHCP client • Built-in DHCP client software in Windows and UNIX operating systems • DHCP Server • Manages address pools and related configuration of Windows and UNIX servers • DHCP relay agent • Intercepts address requests • Repackages requests and unicasts to a DHCP server Guide to TCP/IP, Second Edition

  8. DHCP Lease Types • Two types of address leases • Manual address lease • Dynamic address lease • Typical IP addressing schemes • Servers have fixed IP addresses • Routers have fixed IP addresses • Clients use dynamic IP Addresses Guide to TCP/IP, Second Edition

  9. More About DHCP Leases • IPCONFIG command supports the /release and /renew switches • How DHCP integrates with DSN • Server address are advertised using DNS • DNS is not a dynamic environment • Client address are resolved when using email addresses • User@domain.name Guide to TCP/IP, Second Edition

  10. Understanding IP Address Management With DHCP • Booting for the first time or after a lease expires • DHCP Discovery • Discovery broadcast • Renewal process • Rebinding process • Client must completely release its address if rebinding fails • Servers and clients use PING and ARP as error prevention methods Guide to TCP/IP, Second Edition

  11. The Standard Address Discovery Process • DHCP Discovery process uses four packets • DHCP Discover packet • DHCP Offer packet • DHCP Request packet • DHCP Acknowledgment packet Guide to TCP/IP, Second Edition

  12. The Standard Address Discovery Process (cont.) Guide to TCP/IP, Second Edition

  13. The Discover Packet • Client broadcasts a Discover Packet • Client hardware address • Source IP address 0.0.0.0 • Destination address 255.255.255.255 • Preferred address • Message Type value 1 • Client Identifier • DHCP options Guide to TCP/IP, Second Edition

  14. The Discover Packet (cont.) • DHCP options • Option 1: Client’s subnet mask • Option 3: Routers on the client’s subnet • Option 6: Domain name servers • Option 15: Domain name • Option 44: NetBIOS over TCP/IP name servers • Option 46: NetBIOS over TCP/IP node type • Option 47: NetBIOS over TCP/IP scope • Option 57: Maximum DHCP message size • Option 255: End of options Guide to TCP/IP, Second Edition

  15. The Discover Packet (cont.) Guide to TCP/IP, Second Edition

  16. The Offer Packet • DHCP server sends the Offer packet • An IP address is offered • Packet is sent by unicast Guide to TCP/IP, Second Edition

  17. The Offer Packet (cont.) Guide to TCP/IP, Second Edition

  18. The Request Packet • DHCP Request packet • DHCP Decline packet Guide to TCP/IP, Second Edition

  19. The Request Packet (cont.) Guide to TCP/IP, Second Edition

  20. The Acknowledgment Packet • Sent from Server • Contains configuration options requested by client • Duplicate IP address test Guide to TCP/IP, Second Edition

  21. The Acknowledgment Packet (cont.) Guide to TCP/IP, Second Edition

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