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Chabot College

Chabot College. ELEC 99.05 IP Address Distribution Methods. IP Address Distribution Methods:. Manual Host Configuration RARP BOOTP DHCP. Manual Host Configuration. Required elements: IP Address Subnet Mask Default Gateway Typical additional elements: Domain Name Server Address

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Chabot College

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  1. Chabot College ELEC 99.05 IP Address Distribution Methods

  2. IP Address Distribution Methods: • Manual Host Configuration • RARP • BOOTP • DHCP

  3. Manual Host Configuration • Required elements: • IP Address • Subnet Mask • Default Gateway • Typical additional elements: • Domain Name Server Address • Default Domain Suffix

  4. Windows Host Configuration • On IP Address tab: • IP Address • Subnet Mask

  5. Windows Host Configuration • On Gateway tab: • Default Gateway

  6. Windows Host Configuration • On DNS Configuration tab: • Domain Name Server Address • Default Domain Suffix • Host Name(used in dynamic DNS)

  7. RARP • RARP, or Reverse Address Resolution Protocol. • Like ARP, used to map MAC address to IP addresses. • Works in reverse - used by devices to find their own IP address. • Typically not used on PCs.

  8. RARP • What kind of device would not know its own IP address?

  9. Diskless Workstations • Diskless workstations have no permanent storage (like a hard drive) to store network configurations. • Diskless workstations will know their own MAC address because it’s burned in to the card, but they have to use RARP to find their IP.

  10. FF-FF-FF-FF-FF-FF RARP request • Diskless workstations will send a RARP request, which is a Layer-2 broadcast.

  11. RARP reply • Only a RARP server can respond to a RARP request. • RARP servers maintain a table of IP to MAC address mappings for RARP clients. • During the boot process, RARP clients call the RARP server to obtain their IP configuration information.

  12. BOOTP • Bootstrap Protocol • Specified in RFC 951 • Like RARP, maps IP address to MAC addresses. • Mappings maintained in a data table on a BOOTP server. • Used for PCs

  13. BOOTP • Client sends a bootrequest packet - a Layer 3 broadcast (255.255.255.255) • BOOTP server responds with a bootreply packet containing client’s IP address and gateway IP address.

  14. BOOTP • Much more convenient than manual configuration • Neverthless, requires tedious maintenance of bootp table: • Today, DHCP has largely replaced BOOTP. hamilton 1 02.60.8c.06.34.98 36.19.0.5 burr 1 02.60.8c.34.11.78 36.44.0.12 101-gateway 1 02.60.8c.23.ab.35 36.44.0.32 mjh-gateway 1 02.60.8c.12.32.bc 36.42.0.64 welch-tipa 1 02.60.8c.22.65.32 36.47.0.14 welch-tipb 1 02.60.8c.12.15.c8 36.46.0.12

  15. DHCP • Dynamic Host Configuration Protocol • Specified in RFC 2131 • Based on the BOOTP protocol. Adds automatic allocation of reusable addresses. • Widely used for PCs. • Most ISPs use DHCP for residential customers.

  16. DHCP • Like BOOTP: • Client sends an IP broadcast datagram. • DHCP server returns packet containing IP address of client and gateway.

  17. DHCP • Unlike BOOTP: • Server can return additional information and provide a complete IP configuration: • Subnet mask • Domain Name Server address • Addresses are drawn from a shared pool, so 15 intermittent users can compete for 10 available addresses - an advantage.

  18. DHCP • Unlike BOOTP: • Addresses are dynamic - they may change each time a host boots. • Addresses are granted for a limited period of time - a “lease” time. • When a lease expires, the address is available to another host. • By default, hosts attempt to renegotiate and extend their lease when 50% of the lease time is up.

  19. DHCP Lease • Run winipcfg on your curriculum PC • Click theMore Info>> button • When does your current lease expire?

  20. Configuring Windows Hosts for DHCP • SelectObtain an “IP address automatically” • Most DHCP servers return a complete TCP/IP configuration. • You’re done!

  21. DHCP Server Failure • Most networks have a centralized DHCP server. What happens if it fails? • Hosts that are running will continue until: • their lease expires • they shut down • Hosts that boot up will fail to connect to the network because they cannot obtain an IP address.

  22. DHCP & Network Structure • Remember, the DHCP Discover packet is a Layer 3 broadcast packet, with address 255.255.255.255. • By default, routers do not forward broadcast traffic.

  23. DHCP & Network Structure • How will the client’s DHCP Discover packet reach the centralized DHCP server over a routed network?

  24. DHCP & Network Structure • The router can be configured to forward broadcast traffic only on a particular port (a Layer 4 concept).

  25. DHCP - Benefits • Low maintenance • Provides complete IP configuration • Easy to renumber your network - just change the address range covered by the DHCP server

  26. DHCP - Tradeoffs • DHCP server presents a “single point of failure” • DHCP cannot be a complete solution because...

  27. Address Allocation • Do we want every address to be allocated in this dynamically by DHCP? • Which types of hosts should have addresses that are static - that never change?

  28. Address Allocation • What about servers? • What would happen if a server had a different address each day you try to reach it? • Clearly, some hosts should have static addresses that don’t depend on a DHCP server.

  29. IP Host Address Standards DHCP is great for workstations, but not so great for servers or fixed parts of the network (e.g. the default gateway)

  30. IP Host Address Standards • Typical standards provide an address range for: • Network infrastructure & devices (e.g. routers, default gateway) • Hosts with fixed IP addresses • Hosts with addresses served automatically by DHCP • Printers or other special device classes • Testing

  31. CLPCCD IP Host Standards Host #Use . 0-9 Infrastructure (Network devices) 10-29 IP Hosts w/ static addresses 30-199 DHCP-Served Clients 200-229 Unassigned (use for Lab PCs) 230-239 Printers 240-249 Test Addresses 250-254 Reserved

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