Operation Manual – DHCPH3C S5600 Series Ethernet Switches Chapter 1 DHCP Overview1-2Figure 1-1 Typical DHCP application1.2 DHCP IP Address Assignment1.2.1 IP Address Assignment PolicyCurrently, DHCP provides the following three IP address assignment policies to meetthe requirements of different clients:z Manual assignment. The administrator configures static IP-to-MAC bindings forsome special clients, such as a WWW server. Then the DHCP server assignsthese fixed IP addresses to the clients.z Automatic assignment. The DHCP server assigns IP addresses to DHCP clients.The IP addresses will be occupied by the DHCP clients permanently.z Dynamic assignment. The DHCP server assigns IP addresses to DHCP clients forpredetermined period of time. In this case, a DHCP client must apply for an IPaddress again at the expiration of the period. This policy applies to most clients.1.2.2 Obtaining IP Addresses DynamicallyA DHCP client undergoes the following four phases to dynamically obtain an IP addressfrom a DHCP server:1) Discover: In this phase, the DHCP client tries to find a DHCP server bybroadcasting a DHCP-DISCOVER packet.2) Offer: In this phase, the DHCP server offers an IP address. After the DHCP serverreceives the DHCP-DISCOVER packet from the DHCP client, it chooses anunassigned IP address from the address pool according to the priority order of IPaddress assignment and then sends the IP address and other configurationinformation together in a DHCP-OFFER packet to the DHCP client. The sendingmode is decided by the flag filed in the DHCP-DISCOVER packet, refer to sectionDHCP Packet Format for details.3) Select: In this phase, the DHCP client selects an IP address. If more than oneDHCP server sends DHCP-OFFER packets to the DHCP client, the DHCP client
