DHCP （動態主機設定通訊協定）基本概念

發行項
10/06/2023

動態主機設定通訊協定（DHCP）是 RFC 1541 所定義的標準通訊協定（由 RFC 2131 取代），可讓伺服器動態地將 IP 位址和組態資訊散發給用戶端。 DHCP 伺服器通常至少會提供此基本資訊給用戶端：

IP 位址
子網路遮罩
預設閘道

您也可以提供其他資訊，例如功能變數名稱服務（DNS）伺服器位址和 Windows 網際網路名稱服務（WINS）伺服器位址。系統管理員會使用剖析至用戶端的選項來設定 DHCP 伺服器。

相關資訊

下列 Microsoft 產品提供 DHCP 用戶端功能：

Windows NT Server 3.5、3.51 和 4.0 版
Windows NT 工作站 3.5、3.51 和 4.0 版
Windows 95
適用于 MS-DOS 的 Microsoft 網路用戶端 3.0 版
適用于 MS-DOS 的 Microsoft LAN Manager 用戶端 2.2c 版
Microsoft TCP/IP-32 for Windows for Workgroups 3.11、3.11a 和 3.11b 版

不同的 DHCP 用戶端支援可從 DHCP 伺服器接收的不同選項。

下列 Microsoft 伺服器作業系統提供 DHCP 伺服器功能：

Windows NT Server 3.5 版
Windows NT Server 3.51 版
Windows NT Server 4.0 版

當用戶端在設定為接收 DHCP 資訊之後第一次初始化時，它會起始與伺服器的交談。

以下是用戶端與伺服器之間交談的摘要資料表，後面接著進程的封包層級描述：

Source Dest Source Dest Packet
 MAC addr MAC addr IP addr IP addr Description
 -----------------------------------------------------------------
 Client Broadcast 0.0.0.0 255.255.255.255 DHCP Discover
 DHCPsrvr Broadcast DHCPsrvr 255.255.255.255 DHCP Offer
 Client Broadcast 0.0.0.0 255.255.255.255 DHCP Request
 DHCPsrvr Broadcast DHCPsrvr 255.255.255.255 DHCP ACK

DHCP 用戶端與 DHCP 伺服器之間的詳細交談如下所示：

DHCPDISCOVER

用戶端會傳送 DHCPDISCOVER 封包。以下是網路監視器擷取的摘錄，其中顯示 DHCPDISCOVER 封包的 IP 和 DHCP 部分。在 [IP] 區段中，您可以看到目的地位址為 255.255.255.255，來源位址為 0.0.0.0。 DHCP 區段會將封包識別為探索封包，並使用網路卡的實體位址在兩個位置識別用戶端。請注意 CHADDR 欄位中的值和 DHCP：用戶端識別碼欄位相同。


IP: ID = 0x0; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 0 (0x0)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x39A6
 IP: Source Address = 0.0.0.0
 IP: Destination Address = 255.255.255.255
 IP: 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 Ethernet
 DHCP: 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 Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 0.0.0.0
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP Discover
 DHCP: Client-identifier = (Type: 1) 08 00 2b 2e d8 5e
 DHCP: Host Name = JUMBO-WS
 DHCP: Parameter Request List = (Length: 7) 01 0f 03 2c 2e 2f 06
 DHCP: End of this option field

DHCPOFFER

DHCP 伺服器會傳送 DHCPOFFER 封包來回應。在下列擷取摘錄的 IP 區段中，來源位址現在是 DHCP 伺服器 IP 位址，而目的地位址是廣播位址 255.255.255.255。 DHCP 區段會將封包識別為供應專案。 [YIADDR] 欄位會填入伺服器提供用戶端的 IP 位址。請注意，CHADDR 欄位仍然包含要求用戶端的實體位址。此外，我們也會在 [DHCP 選項欄位] 區段中看到伺服器與 IP 位址一起傳送的各種選項。在此情況下，伺服器會傳送子網路遮罩、預設閘道（路由器）、租用時間、WINS 伺服器位址（NetBIOS 名稱服務），以及 NetBIOS 節點類型。


IP: ID = 0x3C30; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 15408 (0x3C30)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x2FA8
 IP: Source Address = 157.54.48.151
 IP: Destination Address = 255.255.255.255
 IP: Data: Number of data bytes remaining = 308 (0x0134)

DHCP: Offer (xid=21274A1D)
 DHCP: Op Code (op) = 2 (0x2)
 DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet
 DHCP: 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 Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 157.54.50.5
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP Offer
 DHCP: Subnet Mask = 255.255.240.0
 DHCP: Renewal Time Value (T1) = 8 Days, 0:00:00
 DHCP: Rebinding Time Value (T2) = 14 Days, 0:00:00
 DHCP: IP Address Lease Time = 16 Days, 0:00:00
 DHCP: Server Identifier = 157.54.48.151
 DHCP: Router = 157.54.48.1
 DHCP: NetBIOS Name Service = 157.54.16.154
 DHCP: NetBIOS Node Type = (Length: 1) 04
 DHCP: End of this option field

DHCPREQUEST

用戶端會傳送 DHCPREQUEST 來回應 DHCPOFFER。在下列擷取的 IP 區段中，用戶端的來源位址仍然是 0.0.0.0，封包的目的地仍然是 255.255.255.255。用戶端會保留 0.0.0.0，因為用戶端尚未收到來自伺服器驗證，無法開始使用提供的位址。目的地仍會廣播，因為一個以上的 DHCP 伺服器可能已回應，而且可能會保留提供給用戶端的供應專案保留。這可讓其他 DHCP 伺服器知道他們可以釋放其提供的位址，並將它們傳回其可用的集區。 DHCP 區段會將封包識別為 [要求]，並使用 [DHCP：要求的位址] 欄位來驗證提供的位址。 [DHCP：伺服器識別碼] 欄位會顯示提供租用之 DHCP 伺服器的 IP 位址。


IP: ID = 0x100; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 256 (0x100)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x38A6
 IP: Source Address = 0.0.0.0
 IP: Destination Address = 255.255.255.255
 IP: Data: Number of data bytes remaining = 308 (0x0134)

DHCP: Request (xid=21274A1D)
 DHCP: Op Code (op) = 1 (0x1)
 DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet
 DHCP: 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 Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 0.0.0.0
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP Request
 DHCP: Client-identifier = (Type: 1) 08 00 2b 2e d8 5e
 DHCP: Requested Address = 157.54.50.5
 DHCP: Server Identifier = 157.54.48.151
 DHCP: Host Name = JUMBO-WS
 DHCP: Parameter Request List = (Length: 7) 01 0f 03 2c 2e 2f 06
 DHCP: End of this option field

DHCPACK

DHCP 伺服器會以 DHCPACK 回應 DHCPREQUEST，從而完成初始化週期。來源位址是 DHCP 伺服器 IP 位址，而目的地位址仍然是 255.255.255.255。 YIADDR 欄位包含用戶端的位址，而 CHADDR 和 DHCP：用戶端識別碼欄位是要求用戶端中網路卡的實體位址。 DHCP 選項區段會將封包識別為 ACK。


IP: ID = 0x3D30; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 15664 (0x3D30)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x2EA8
 IP: Source Address = 157.54.48.151
 IP: Destination Address = 255.255.255.255
 IP: Data: Number of data bytes remaining = 308 (0x0134)

DHCP: ACK (xid=21274A1D)
 DHCP: Op Code (op) = 2 (0x2)
 DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet
 DHCP: 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 Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 157.54.50.5
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP ACK
 DHCP: Renewal Time Value (T1) = 8 Days, 0:00:00
 DHCP: Rebinding Time Value (T2) = 14 Days, 0:00:00
 DHCP: IP Address Lease Time = 16 Days, 0:00:00
 DHCP: Server Identifier = 157.54.48.151
 DHCP: Subnet Mask = 255.255.240.0
 DHCP: Router = 157.54.48.1
 DHCP: NetBIOS Name Service = 157.54.16.154
 DHCP: NetBIOS Node Type = (Length: 1) 04
 DHCP: End of this option field

如果用戶端先前有 DHCP 指派的 IP 位址且重新開機，用戶端將會特別要求特殊 DHCPREQUEST 封包中先前租用的 IP 位址。來源位址為 0.0.0.0，而目的地是廣播位址 255.255.255.255。 Microsoft 用戶端會將 DHCP 選項欄位 DHCP：要求的位址填入先前指派的位址。嚴格符合 RFC 規範的用戶端會將要求的位址填入 CIADDR 欄位。 Microsoft DHCP 伺服器將接受其中一項。


IP: ID = 0x0; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 0 (0x0)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x39A6
 IP: Source Address = 0.0.0.0
 IP: Destination Address = 255.255.255.255
 IP: Data: Number of data bytes remaining = 308 (0x0134)

DHCP: Request (xid=2757554E)
 DHCP: Op Code (op) = 1 (0x1)
 DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet
 DHCP: Hardware Address Length (hlen) = 6 (0x6)
 DHCP: Hops (hops) = 0 (0x0)
 DHCP: Transaction ID (xid) = 660034894 (0x2757554E)
 DHCP: Seconds (secs) = 0 (0x0)
 DHCP: Flags (flags) = 0 (0x0)
 DHCP: 0............... = No Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 0.0.0.0
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP Request
 DHCP: Client-identifier = (Type: 1) 08 00 2b 2e d8 5e
 DHCP: Requested Address = 157.54.50.5
 DHCP: Host Name = JUMBO-WS
 DHCP: Parameter Request List = (Length: 7) 01 0f 03 2c 2e 2f 06
 DHCP: End of this option field

此時，伺服器可能會或可能不會回應。 Windows NT DHCP 伺服器的行為取決於所使用的作業系統版本，以及超複製等其他因素。如果伺服器判斷用戶端仍然可以使用位址，它將會保持無訊息或 ACK DHCPREQUEST。如果伺服器判斷用戶端不能有位址，則會傳送 NACK。


IP: ID = 0x3F1A; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 16154 (0x3F1A)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x2CBE
 IP: Source Address = 157.54.48.151
 IP: Destination Address = 255.255.255.255
 IP: Data: Number of data bytes remaining = 308 (0x0134)

DHCP: NACK (xid=74A005CE)
 DHCP: Op Code (op) = 2 (0x2)
 DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet
 DHCP: Hardware Address Length (hlen) = 6 (0x6)
 DHCP: Hops (hops) = 0 (0x0)
 DHCP: Transaction ID (xid) = 1956644302 (0x74A005CE)
 DHCP: Seconds (secs) = 0 (0x0)
 DHCP: Flags (flags) = 0 (0x0)
 DHCP: 0............... = No Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 0.0.0.0
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP NACK
 DHCP: Server Identifier = 157.54.48.151
 DHCP: End of this option field

用戶端接著會開始探索程式，但 DHCPDISCOVER 封包仍會嘗試租用相同的位址。在許多情況下，用戶端會取得相同的位址，但可能不會。


IP: ID = 0x100; Proto = UDP; Len: 328
 IP: Version = 4 (0x4)
 IP: Header Length = 20 (0x14)
 IP: Service Type = 0 (0x0)
 IP: Precedence = Routine
 IP: ...0.... = Normal Delay
 IP: ....0... = Normal Throughput
 IP: .....0.. = Normal Reliability
 IP: Total Length = 328 (0x148)
 IP: Identification = 256 (0x100)
 IP: Flags Summary = 0 (0x0)
 IP: .......0 = Last fragment in datagram
 IP: ......0. = May fragment datagram if necessary
 IP: Fragment Offset = 0 (0x0) bytes
 IP: Time to Live = 128 (0x80)
 IP: Protocol = UDP - User Datagram
 IP: Checksum = 0x38A6
 IP: Source Address = 0.0.0.0
 IP: Destination Address = 255.255.255.255
 IP: Data: Number of data bytes remaining = 308 (0x0134)

DHCP: Discover (xid=3ED14752)
 DHCP: Op Code (op) = 1 (0x1)
 DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet
 DHCP: Hardware Address Length (hlen) = 6 (0x6)
 DHCP: Hops (hops) = 0 (0x0)
 DHCP: Transaction ID (xid) = 1053902674 (0x3ED14752)
 DHCP: Seconds (secs) = 0 (0x0)
 DHCP: Flags (flags) = 0 (0x0)
 DHCP: 0............... = No Broadcast
 DHCP: Client IP Address (ciaddr) = 0.0.0.0
 DHCP: Your IP Address (yiaddr) = 0.0.0.0
 DHCP: Server IP Address (siaddr) = 0.0.0.0
 DHCP: Relay IP Address (giaddr) = 0.0.0.0
 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E
 DHCP: Server Host Name (sname) = <Blank>
 DHCP: Boot File Name (file) = <Blank>
 DHCP: Magic Cookie = [OK]
 DHCP: Option Field (options)
 DHCP: DHCP Message Type = DHCP Discover
 DHCP: Client-identifier = (Type: 1) 08 00 2b 2e d8 5e
 DHCP: Requested Address = 157.54.51.5
 DHCP: Host Name = JUMBO-WS
 DHCP: Parameter Request List = (Length: 7) 01 0f 03 2c 2e 2f 06
 DHCP: End of this option field

用戶端從 DHCP 伺服器取得的 DHCP 資訊將會有與其相關聯的租用時間。租用時間會定義用戶端可以使用 DHCP 指派資訊的時間長度。當租用達到特定里程碑時，用戶端會嘗試更新其 DHCP 資訊。

若要在 Windows 或 Windows for Workgroups 用戶端上檢視 IP 資訊，請使用 IPCONFIG 公用程式。如果用戶端是 Windows 95，請使用 WINIPCFG。

參考資料

如需 DHCP 的詳細資訊，請參閱 RFC1541 和 RFC2131。 RFC 可透過網際網路在多個網站取得，例如： http://www.rfc-editor.org/ 和 http://www.tech-nic.qc.ca/

DHCP （動態主機設定通訊協定） 基本概念