How does the DHCP server and client works?

1. Dynamic Host Configuration Protocol (DHCP) RFC 2131 Presentation By: Ranjeet Saini (Raini). Team Leader: Olivia Wang. Date: Wednesday, March 24, 2004.

12. BOOTP Operation Port 67/UDP Port 68/UDP BOOTP UDP IP SA/DA BOOTP Client (A) BOOTP Server (B) BOOTP request B | A 67 | 68 BOOTP request BOOTP reply B | A 67 | 68 BOOTP reply

13. BOOTP PDU Format Vender Specific Area (up to 64-Bytes) Boot file name (128-Bytes) Server name (64-Bytes) Client hardware address (16-Bytes) Gateway IP address (4-Bytes) Server IP address (4-Bytes) Your IP address (4-Bytes) Client IP address (4-Bytes) Unused (2-Bytes) Number of seconds (2-Bytes) Transaction ID (4-Bytes) Hop Count (8-Bit) Hardware Length (8-Bit) Hardware Type (8-Bit) Operation Code (8-Bit)

14. BOOTP Problem Internet Router 192.168.1.1 Boot Server 192.168.1.2 DNS Server 192.168.1.3 File Server 192.168.1.4 ee:34:d6:75:03:e2 e3:23:d2:75:05:f1 e6:34:d6:34:05:44 e6:75:e2:64:66:38 I don’t know, I’ve never seen you here before. New Roaming Client (Ether or Wireless) What’s my network configuration?

22. DHCP PDU Format Hop Count (8-Bit) Options (up to 312 bytes) Boot file name (128-Bytes) Server name (64-Bytes) Client hardware address (16-Bytes) Gateway IP address (4-Bytes) Server IP address (4-Bytes) Your IP address (4-Bytes) Client IP address (4-Bytes) Flag (1 bit) | (15 unused bits) Number of seconds Transaction ID (4-Bytes) Hardware Length (8-Bit) Hardware Type (8-Bit) Operation Code (8-Bit)

24. Typical Options Tag(0) Tag Length(N) Value Tag (255) Padding N bytes End of options 66 TFTP Server 54 Server Identifier 55 Parameter Request List 4 DNS name server 53 DHCP Message 3 Time server 61 Client Identifier 69 SMTP Server 72 WWW Server 37 TCP Default TTL 13 Boot File size 1 Subnet Mask

26. DHCP Client State Diagram Selecting Requesting Bound Renewing Rebinding Initializing DHCPDISCOVER DHCPREQUEST DHCPACK DHCPOFFER Lease 87.5% Expired DHCPREQUEST DHCPACK DHCPACK DHCPNACK Lease Expired Lease 50% Expired DHCPREQUEST DHCPNACK Lease Expired DHCPRELEASE Lease Cancelled

27. Allocating New Address DHCP Server-1 (not selected) DHCP Server-2 (selected) DHCP Client Client attempts to discover available DHCP servers Servers reply with address offers Client selects which offer to accept Client notifies servers of choice Server acknowledges client use of address Client gives up use of address DHCPDISCOVER DHCPDISCOVER DHCPOFFER DHCPOFFER DHCPREQUEST DHCPREQUEST DHCPACK DHCPRELEASE

28. Address Renewing Scenario DHCP Server-1 (not selected) DHCP Server-2 (selected) DHCP Client Client makes request Server acknowledges request; lease begins Time passes; 50% of lease expires Client makes request to renew address No response from server, client times out and sends request again Server responds with negative acknowledgement, address can not be renewed Client begins discovery phase to find a new address to lease DHCPREQUEST DHCPACK DHCPREQUEST DHCPNACK DHCPDISCOVER DHCPDISCOVER DHCPREQUEST

33. DHCP Client Test

40. DHCP Server Test

46. Thanks