動態主機配置協議 (DHCP) 是 RFC 1541（已被 RFC 2131 取代）定義的標準協議，該協議答應服務器向客戶端動態分配 ip 地址和配置信息。通常，DHCP 服務器至少向客戶端提供以下基本信息： • IP 地址

• 子網掩碼

• 默認網關 它還可以提供其他信息，如域名服務 (DNS) 服務器的地址和 Windows Internet 名稱服務 (WINS) 服務器的地址。系統治理員配置 DHCP 服務器分配給客戶端的選項。

當客戶端被配置為接收 DHCP 信息后首次初始化時，它將啟動與服務器的對話。

以下是客戶端和服務器之間對話的摘要表，最后一列是數據包級的過程說明：

Source     Dest        Source     Dest              PacketMAC addr   MAC addr    IP addr    IP addr           Description-----------------------------------------------------------------Client     Broadcast   0.0.0.0    255.255.255.255   DHCP DiscoverDHCPsrvr   Broadcast   DHCPsrvr   255.255.255.255   DHCP OfferClient     Broadcast   0.0.0.0    255.255.255.255   DHCP RequestDHCPsrvr   Broadcast   DHCPsrvr   255.255.255.255   DHCP ACK				

DHCP 客戶端和 DHCP 服務器之間的具體對話如下：

DHCPDISCOVER

客戶端發送 DHCPDISCOVER 數據包。以下內容摘自網絡監視器的捕捉信息，顯示了 DHCPDISCOVER 數據包中的 IP 和 DHCP 部分。在 IP 部分，可以看到 Destination 地址是 255.255.255.255，而 Source 地址是 0.0.0.0。DHCP 部分將數據包標識為 Discover 數據包，并使用網卡的物理地址在兩處標識客戶端。注重 CHADDR 字段和 DHCP 中的值：Client Identifier 字段是相同的。

IP:ID = 0x0; PRoto = UDP; Len: 328IP:Version = 4 (0x4)IP:Header Length = 20 (0x14)IP:Service Type = 0 (0x0)IP:Precedence = RoutineIP:...0.... = Normal DelayIP:....0... = Normal ThroughputIP:.....0.. = Normal ReliabilityIP:Total Length = 328 (0x148)IP:Identification = 0 (0x0)IP:Flags Summary = 0 (0x0)IP:.......0 = Last fragment in datagramIP:......0. = May fragment datagram if necessaryIP:Fragment Offset = 0 (0x0) bytesIP:Time to Live = 128 (0x80)IP:Protocol = UDP - User DatagramIP:Checksum = 0x39A6IP:Source Address = 0.0.0.0IP:Destination Address = 255.255.255.255IP:Data:Number of data bytes remaining = 308 (0x0134)DHCP:Discover           (xid=21274A1D)DHCP:Op Code           (op)     = 1 (0x1)DHCP:Hardware Type     (htype)  = 1 (0x1) 10Mb EthernetDHCP:Hardware Address Length (hlen) = 6 (0x6)DHCP:Hops              (hops)   = 0 (0x0)DHCP:Transaction ID    (xid)    = 556223005 (0x21274A1D)DHCP:Seconds           (secs)   = 0 (0x0)DHCP:Flags             (flags)  = 0 (0x0)DHCP:0............... = No BroadcastDHCP:Client IP Address (ciaddr) = 0.0.0.0DHCP:Your   IP Address (yiaddr) = 0.0.0.0DHCP:Server IP Address (siaddr) = 0.0.0.0DHCP:Relay  IP Address (giaddr) = 0.0.0.0DHCP:Client Ethernet Address (chaddr) = 08002B2ED85E