Microsoft KB Archive/257579

= PXE Clients do not receive an IP address from a DHCP server across a router =

Article ID: 257579

Article Last Modified on 3/1/2007

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APPLIES TO


 * Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)
 * Microsoft Windows Server 2003, Standard Edition (32-bit x86)
 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows NT Server 4.0 Enterprise Edition
 * Microsoft Windows NT 4.0 Service Pack 3
 * Microsoft Windows NT 4.0 Service Pack 4
 * Microsoft Windows NT 4.0 Service Pack 5
 * Microsoft Windows NT 4.0 Service Pack 6
 * Microsoft Windows NT 4.0 Service Pack 6a
 * Microsoft BackOffice Server 4.0
 * Microsoft BackOffice Server 4.5
 * Microsoft BackOffice Small Business Server 4.0
 * Microsoft BackOffice Small Business Server 4.0a
 * Microsoft BackOffice Small Business Server 4.5

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This article was previously published under Q257579







SUMMARY
Pre-Boot Execution Environment (PXE) clients require an Internet Protocol (IP) address from a Dynamic Host Configuration Protocol (DHCP) server to begin the installation process from a Remote Installation Services (RIS) server. If the PXE client is located across a router from the DHCP server and/or the RIS server, the client may not receive an IP address from the DHCP server or configuration information from the RIS server. If these two pieces of information are not available, the installation on the PXE client does not work.



MORE INFORMATION
DHCP clients located across a router from a DHCP server require that the router be configured to forward DHCP traffic to a DHCP server on a remote subnet. This traffic is broadcast traffic and routers do not normally forward broadcast traffic unless configured to do so. A network router can be a hardware-based router, such as those manufactured by the Cisco Corporation or software-based such as Microsoft's Routing and Remote Access Services (RRAS). In either case, you need to configure the router to relay DHCP traffic to designated DHCP servers. The DHCP server IP addresses are configured on the router on a per-interface basis using IP helper functionality, or in the case of RRAS, using the DHCP relay agent. The following example shows an IP helper configuration:   ip forward-protocol udp !  interface ethernet 1 ip address 10.3.0.1 255.255.0.0 ip helper-address 10.2.0.2 For additional information about configuring DHCP servers on third-party router products, consult the appropriate configuration documentation that comes with the product.

Configuring the DHCP Relay Agent on RRAS in Microsoft Windows NT 4.0
Use the following steps to configure the DHCP relay agent in Windows NT 4.0:
 * 1) Click Start, point to Programs, point to Administrative Tools, and then click Routing and RAS Admin.
 * 2) Expand the IP Routing folder, right-click Summary, and then click Add Routing Protocol.
 * 3) Click DHCP Relay Agent in the list, and then click OK.

The DHCP Relay Agent option is now available in the IP Routing folder. To configure the DHCP relay agent:
 * 1) Right-click DHCP Relay Agent, and then click Configure DHCP Relay Agent.
 * 2) A dialog box is displayed and you can type the IP addresses of the DHCP servers. Because this is a PXE client that needs to communicate with a RIS server, you also need to add the IP address of the RIS server. This allows the relay agent to simultaneously forward DHCP broadcast traffic to both the DHCP servers and the RIS server.
 * 3) After you have added all the required IP addresses, you need to choose an interface to perform the relay function. Right-click DHCP Relay Agent, and then click Add interface.
 * 4) A dialog box that lists all available interfaces on the RRAS server is displayed. Select the interface that is on the same subnet as the PXE client, accept the defaults (you may need to modify the hop count, depending on the location of the DHCP server and/or RIS server), and then click OK.

To determine if the DHCP relay agent is functioning properly, use the following steps:   Using Network Monitor to analyze DHCP traffic, ensure that the giaddr field in the DHCP packets is the IP address of the relay interface on the RRAS server:   DHCP: Discover           (xid=7DD04550) DHCP: Op Code          (op)     = 1 (0x1) DHCP: Hardware Type    (htype)  = 1 (0x1) 10Mb Ethernet DHCP: Hardware Address Length (hlen) = 6 (0x6) DHCP: Hops             (hops)   = 1 (0x1) DHCP: Transaction ID   (xid)    = 2110801232 (0x7DD04550) DHCP: Seconds          (secs)   = 4 (0x4) DHCP: Flags            (flags)  = 128 (0x80) DHCP: 1............... = 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) = 11.11.1.1 DHCP: Client Ethernet Address (chaddr) = 00C04F45D07D DHCP: Server Host Name (sname)  =  DHCP: Boot File Name   (file)   =  DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field     (options) DHCP: DHCP Message Type     = DHCP Discover DHCP: Parameter Request List = (Length: 5) 01 03 3c 2b 43 DHCP: Maximum DHCP Message Size = (Length: 2) 04 ec   DHCP: Unrecognized Option    = 97 (0x61) DHCP: Unrecognized Option   = 93 (0x5D) DHCP: Unrecognized Option   = 94 (0x5E) DHCP: Client Class information = (Length: 9) 50 58 45 43 6c 69 65 6e 74 DHCP: End of this option field   Look at the number of Requests Received and Replies Received in the right pane of the RRAS Administrator interface associated with the relay interface.

The DHCP server and the RIS server both receive the Discover packets and both reply with an Offer packet. The DHCP server offer includes the PXE client IP address and any additional options that are configured (router, DNS server, WINS server, and so on):   DHCP: Offer              (xid=7DD04550) 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)    = 2110801232 (0x7DD04550) DHCP: Seconds          (secs)   = 0 (0x0) DHCP: Flags            (flags)  = 128 (0x80) DHCP: 1............... = Broadcast DHCP: Client IP Address (ciaddr) = 0.0.0.0 DHCP: Your  IP Address (yiaddr) = 11.11.1.18 DHCP: Server IP Address (siaddr) = 10.10.1.1 DHCP: Relay IP Address (giaddr) = 11.11.1.1 DHCP: Client Ethernet Address (chaddr) = 00C04F45D07D DHCP: Server Host Name (sname)  =  DHCP: Boot File Name   (file)   = <Blank> DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field     (options) DHCP: DHCP Message Type     = DHCP Offer DHCP: Subnet Mask           = 255.0.0.0 DHCP: Renewal Time Value (T1) = 4 Days, 0:00:00 DHCP: Rebinding Time Value (T2) = 7 Days, 0:00:00 DHCP: IP Address Lease Time = 8 Days,  0:00:00 DHCP: Server Identifier     = 10.10.1.1 DHCP: Router                = 11.11.1.1 DHCP: End of this option field The RIS server offer only includes the RIS server IP address, for which the client sends an ARP request to continue with the software installation process: <pre class="fixed_text">  DHCP: Offer              (xid=7DD04552) 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)    = 2110801234 (0x7DD04552) DHCP: Seconds          (secs)   = 0 (0x0) DHCP: Flags            (flags)  = 128 (0x80) DHCP: 1............... = Broadcast DHCP: Client IP Address (ciaddr) = 0.0.0.0 DHCP: Your  IP Address (yiaddr) = 0.0.0.0 DHCP: Server IP Address (siaddr) = 10.10.1.2 DHCP: Relay IP Address (giaddr) = 11.11.1.1 DHCP: Client Ethernet Address (chaddr) = 00C04F45D07D DHCP: Server Host Name (sname)  = <Blank> DHCP: Boot File Name   (file)   = <Blank> DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field     (options) DHCP: DHCP Message Type     = DHCP Offer DHCP: Server Identifier     = 10.10.1.2 DHCP: Client Class information = (Length: 9) 50 58 45 43 6c 69 65 6e 74 DHCP: Option MUST NOT be Present DHCP: End of this option field </li></ol>

Configuring the DHCP Relay Agent in Microsoft Windows 2000 and in Microsoft Windows Server 2003
Configuring the DHCP Relay Agent in Windows 2000 and in Windows Server 2003 is similar to the process used in Windows NT 4.0: <ol> Click Start, point to Programsor to All Programs, point to Administrative Tools, and then click Routing and Remote Access.</li> Assuming that you have already installed RRAS, under IP routing, right-click General, and then click New Routing Protocol.

NOTE: From this point the installation and configuration of the DHCP relay agent is the same as the process for Windows NT 4.0, although the screens may be slightly different in appearance.</li>  After the PXE client is configured with an IP address, it continues its conversation with the RIS server with another DHCP Request packet: <pre class="fixed_text">  DHCP: Request            (xid=7DD04552) 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)    = 2110801234 (0x7DD04552) DHCP: Seconds          (secs)   = 7 (0x7) DHCP: Flags            (flags)  = 0 (0x0) DHCP: 0............... = No Broadcast DHCP: Client IP Address (ciaddr) = 11.11.1.18 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) = 00C04F45D07D DHCP: Server Host Name (sname)  = <Blank> DHCP: Boot File Name   (file)   = <Blank> DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field     (options) DHCP: DHCP Message Type     = DHCP Request DHCP: Parameter Request List = (Length: 5) 01 03 3c 2b 43 DHCP: Maximum DHCP Message Size = (Length: 2) 04 ec   DHCP: Unrecognized Option    = 97 (0x61) DHCP: Unrecognized Option   = 93 (0x5D) DHCP: Unrecognized Option   = 94 (0x5E) DHCP: Client Class information = (Length: 9) 50 58 45 43 6c 69 65 6e 74 DHCP: End of this option field </li>  The RIS server sends an Ack packet with the configuration information the PXE client needs to continue with the installation process: <pre class="fixed_text">  DHCP: ACK                (xid=7DD04552) 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)    = 2110801234 (0x7DD04552) DHCP: Seconds          (secs)   = 0 (0x0) DHCP: Flags            (flags)  = 0 (0x0) DHCP: 0............... = No Broadcast DHCP: Client IP Address (ciaddr) = 11.11.1.18 DHCP: Your  IP Address (yiaddr) = 0.0.0.0 DHCP: Server IP Address (siaddr) = 10.10.1.2 DHCP: Relay IP Address (giaddr) = 0.0.0.0 DHCP: Client Ethernet Address (chaddr) = 00C04F45D07D DHCP: Server Host Name (sname)  = risbox.tracetest.com DHCP: Boot File Name   (file)   = OSChooser\i386\startrom.com DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field     (options) DHCP: DHCP Message Type     = DHCP ACK DHCP: Server Identifier     = 10.10.1.2 DHCP: Unrecognized Option   = 97 (0x61) DHCP: Client Class information = (Length: 9) 50 58 45 43 6c 69 65 6e 74 DHCP: Option MUST NOT be Present DHCP: End of this option field </li> Normal DHCP conversations between a DHCP server and a client occur on UDP Ports 67 (server) and 68 (client). The conversations between a PXE client and a RIS server during an installation occur on UDP Ports 68 (client) and 4011 (server).</li></ol>

NOTE: For information based on tests conducted with ROM versions .99j 02 and .99N on Intel computers, refer to the following Microsoft Knowledge Base article:

244454 PXE Client with Revision .99j Boot ROM May Not Be Able to Contact RIS Server

For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:

244036 Description of PXE Interaction Among PXE Client, DHCP, and RIS Server

255952 Unable to Contact DHCP Server with RIS Boot Disk

120932 DHCP: Spanning Multiple Subnets

161571 Using DHCP Superscopes to Serve Multiple Logical Subnets

197197 DHCP Clients Are Unable to Get IP Address from a DHCP Server

Keywords: kbenv kbinfo kbnetwork KB257579

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