IP Services: ARP, RARP, DHCP, BOOTP

ARP and Proxy Arp:

  • method to learn another hosts MAC address
  • all 0’s in des MAC
  • ARP protocol type: 0x0806
  • Proxy Arp: if a router can route packet to the target host in another subnet, router uses proxy ARP on behalf of the target.

RARP, BOOTP and DHCP

  • main function: how host can discover it’s own IP address plus other details
  • RARP: same old ARP message but uses it’s own MAC address as TARGET and IP address of 0.0.0.0. RARP server must be on the same subnet as the client.
  • BOOTP: commands are encapsulated in an IP and UDP header. Router can forward the BOOTP packets to other subnets. Also allows assignment of: subnet mask, default gateway, DNS address and IP address of a boot server. STILL REQUIRES CONFIGURATION LIKE RARP.
  • DHCP: Router would change the clients DHCP request from a source and destination of 255.255.255.255 to a source of directed broadcast of clients subnet (e.g 10.1.1.255) and destination of DHCP server. DHCP response would be forwarded to destination 10.1.1.255.
    • Only configuration command: ip helper-address <dhcpserverIP> on the inside router interface (client side).
    • DHCP pool includes keys such as: subnet, default gateway, length of lease time, dns domain name.
    • you can use (global) ip dhcp excluded-address command to exclude IP hosts. (global configuration)
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