592 CHAPTER 56: DHCP OVERVIEWDHCP PacketProcessing ModesAfter the DHCP server is enabled on a device, the device processes the DHCPpacket received from a DHCP client in one of the following three modesdepending on your configuration:■ Global address pool: In response to the DHCP packets received from DHCPclients, the DHCP server picks IP addresses from its global address pools andassigns them to the DHCP clients.■ Interface address pool: In response to the DHCP packets received from DHCPclients, the DHCP server picks IP addresses from the interface address pools andassigns them to the DHCP clients. If there is no available IP address in theinterface address pools, the DHCP server picks IP addresses from its globaladdress pool that contains the interface address pool segment and assignsthem to the DHCP clients.■ Trunk: DHCP packets received from DHCP clients are forwarded to an externalDHCP server, which assigns IP addresses to the DHCP clients.You can specify the mode to process DHCP packets. For the configuration of thefirst two modes, see Chapter 57 “DHCP Server Configuration” on page 593. Forthe configuration of the trunk mode, see Chapter 58 “DHCP Relay AgentConfiguration” on page 611.One interface only corresponds to one mode. In this case, the new configurationoverwrites the previous one.Protocols andStandardsProtocol specifications related to DHCP include:■ RFC2131: Dynamic Host Configuration Protocol■ RFC2132: DHCP Options and BOOTP Vendor Extensions■ RFC1542: Clarifications and Extensions for the Bootstrap Protocol
