Dynamic Host Configuration Protocol

CSI 5321 Presented by Junaid Taqui

Wednesday, December 04, 2002 1

What is DHCP ?

 Two Components of DHCP  DHCP is built on a client-server model  DHCP supports three modes of IP-Address allocation Automatic Manual Dynamic Wednesday, December 04, 2002 2

Related Work

 RARP  TFTP  ICMP  BOOTP NIP  ARP  RLP Wednesday, December 04, 2002 3

Definition of useful terms

 DHCP client  DHCP server  BOOTP relay agent  Binding  Lease Wednesday, December 04, 2002 4

Wednesday, December 04, 2002 op (1) htype (1) hlen (1) hops (1) xid (4) secs (2) flags (2) ciaddr (4) yiaddr (4) siaddr (4) giaddr (4) chaddr (16) sname (64) file (128) options (312) Format of DHCP message 5

DHCP Messages

 DHCPDISCOVER - Client broadcast to locate available servers.

 DHCPOFFER - Server to client in response to DHCPDISCOVER with offer of configuration parameters.

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DHCP Messages

 DHCPACK - Server to client with configuration parameters, including committed network address.

 DHCPNAK - Server to client indicating client's notion of network address is incorrect (e.g., client has moved to new subnet) or client's lease as expired  DHCPDECLINE - Client to server indicating network address is already in use. Wednesday, December 04, 2002 7

DHCP Messages

 DHCPRELEASE - Client to server relinquishing network address and canceling remaining lease.  DHCPINFORM - Client to server, asking only for local configuration parameters; client already has externally configured network address. Wednesday, December 04, 2002 8

The Client-Server Protocol

 Client-server interaction - allocating a network address  Client-server interaction - reusing a previously allocated network address Wednesday, December 04, 2002 9

Allocating a network address

SERVER CLIENT SERVER DHCPDISCOVER DHCPDISCOVER DHCPOFFER DHCPOFFER Wednesday, December 04, 2002 DHCPREQUEST DHCPREQUEST DHCPACK DHCPRELEASE 10

Reusing a previously allocated network address

SERVER CLIENT SERVER DHCPREQUEST DHCPREQUEST DHCPACK DHCPACK Initialization complete Subsequent DHCPACKS ignored Wednesday, December 04, 2002 11

References

 Request for Comments:2132 – Dynamic Host Configuration Protocol  http://www.dhcp.org

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