DHCP, Troubleshooting (DHCP Operations Guide)

Troubleshooting (DHCP Operations Guide) in DHCP Operations Guide

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Troubleshooting

Overview

The following table contains troubleshooting tips that should be useful in maintaining this product. The tips are based on known issues and follow the best practices for troubleshooting and problem management outlined by the Incident Management SMF and the Problem Management SMF, both found in the MOF Supporting Quadrant.

  • Problem #1: No IP Address

    Description of Problem: The DHCP client does not have an IP address configured or indicates that its IP address is 0.0.0.0.

    Cause of the problem: The client was not able to contact a DHCP server and obtain an IP address lease, either because of a network hardware failure or because the DHCP server is unavailable.

    Resolution of the problem: Verify that the client computer has a valid functioning network connection. First, check that related client hardware (cables and network adapters) are working properly at the client using basic network and hardware troubleshooting steps. If the client hardware appears to be prepared and functioning properly, check that the DHCP server is available on the network by pinging it from another computer on the same network as the affected DHCP client.

  • Problem #2: Incorrect IP Address

    Description of Problem: The DHCP client appears to have automatically assigned itself an IP address that is incorrect for the current network.

    Cause of the problem: The Windows XP, Windows Millennium Edition (ME), or Windows 98 DHCP client could not find a DHCP server and has used IP autoconfiguration to configure its IP address. In some larger networks, disabling IP autoconfiguration might be desirable for network administration

    Resolution of the problem: First, use the ping command to test connectivity from the client to the server. Next, either verify or manually attempt to renew the client lease. Depending on the network requirements, it might be necessary to disable IP autoconfiguration at the client.

  • Problem #3: Missing Configuration Details

    Description of Problem: The DHCP client appears to be missing some network configuration details or is unable to perform related tasks, such as resolving names.

    Cause of the problem: The client might be missing DHCP options in its leased configuration, either because the DHCP server is not configured to distribute them or because the client does not support the options distributed by the server.

    Resolution of the problem: For Microsoft DHCP clients, verify that the most commonly used and supported options have been configured at the server, scope, client, or class level of options assignment.

  • Problem #4: Incorrect or Incomplete Options

    Description of Problem: The DHCP client appears to have incorrect or incomplete options, such as an incorrect or missing router (default gateway) configured for the subnet on which it is located.

    Cause of the problem: The client has the full and correct set of DHCP options assigned, but its network configuration does not appear to be working correctly. If the DHCP server is configured with an incorrect DHCP router option (option code 3) for the default gateway address of the client, clients running Windows NT, Windows 2000, or Windows XP use the correct address. However, DHCP clients running Windows 95 use the incorrect address.

    Resolution of the problem: Change the IP address list for the router (default gateway) option at the applicable DHCP scope and server. In rare instances, configure the DHCP client to use a specialized list of routers different from other scope clients. In such cases, add a reservation and configure the router option list specifically for the reserved client.

  • Problem #5: Unable to Obtain IP Addresses

    Description of Problem: Many DHCP clients are unable to get IP addresses from the DHCP server.

    Possible Causes and Resolutions of Problem

    1. Cause of the problem: The IP address of the DHCP server was changed, and now DHCP clients cannot get IP addresses.

      Resolution: A DHCP server can only service requests for a scope that has a network ID that is the same as the network ID of its IP address. Ensure that the DHCP server’s IP address is configured correctly. Verify that all IP helpers on routers and DHCP relay agents accurately refer to this IP address.

    2. Cause of the problem: The DHCP clients are located across a router or switch from the subnet where the DHCP server resides and are unable to receive an address from the server.

      Resolution: A DHCP server can provide IP addresses to client computers on remote multiple subnets only if the router or switch that separates them can act as a BOOTP Relay.

      Completing the following steps might correct this problem:

      1. Configure a BOOTP Relay on the client subnet (that is, the same physical network segment). Use the network vendor prescription for configuring the BOOTP Relay.
      2. At the DHCP server, do the following: Configure a scope to match the network address on the other side of the router or switch where the affected clients are located; In the scope, make sure that the subnet mask is correct for the remote subnet; Use a default gateway on the network connection of the DHCP server in such a way that it is not using the same IP address as the switch or router that supports the remote subnet where the clients are located; Do not include this scope (that is, the one for the remote subnet) in superscopes configured for use on the same local subnet or segment where the DHCP server resides; Make sure there is only one logical route between the DHCP server and the remote subnet clients.
    3. Cause of the problem: Multiple DHCP servers exist on the same LAN.

      Resolution: Make sure that multiple DHCP servers on the same LAN are not configured with overlapping scopes.

Problem #6: No Relay Services

Description of Problem: The DHCP Relay Agent is not providing relay services for DHCP clients on a network segment.

Possible Causes and Resolutions of Problem:

  1. Cause of the problem: The interface on the server running routing and remote access that connects to the network segment where the DHCP clients are located is not added to the DHCP Relay Agent IP routing protocol.

    Resolution: Verify that the interface on the server running routing and remote access that connects to the network segment where the DHCP clients are located is added to the DHCP Relay Agent IP routing protocol to enable the DHCP Relay Agent on a router interface.

  2. Cause of the problem: The Relay DHCP packets check box is not selected for the DHCP Relay Agent interface that is connected to the network segment where the DHCP clients are located.

    Resolution: Verify that the Relay DHCP packets check box is selected for the DHCP Relay Agent interface that is connected to the network segment where the DHCP clients are located.

  3. Cause of the problem: The IP addresses of DHCP servers configured on the global properties of the DHCP Relay Agent are incorrect.

    Resolution: Verify that the IP addresses of DHCP servers configured on the global properties of the DHCP Relay Agent are the correct IP addresses for DHCP servers on your internetwork.

  4. Cause of the problem: The correctly configured DHCP servers are not reachable.

    Resolution: From the router with the DHCP Relay Agent enabled, use the ping command to ping each of the DHCP servers that are configured in the global DHCP Relay Agent dialog box. If you cannot ping the DHCP servers from the DHCP Relay Agent router, troubleshoot the lack of connectivity between the DHCP Relay Agent router and the DHCP server or servers.

  5. Cause of the problem: IP packet filtering is preventing the receiving (through input filters) or sending (through output filters) of DHCP traffic.

    Resolution: Verify that IP packet filtering on the router interfaces is not preventing the receiving (through input filters) or sending (through output filters) of DHCP traffic. DHCP traffic uses the User Datagram Protocol (UDP) ports of 67 and 68. Manage packet filters.

  6. Cause of the problem: TCP/IP filtering is preventing the receiving of DHCP traffic.

    Resolution: Verify that TCP/IP filtering on the router interfaces is not preventing the receiving of DHCP traffic. DHCP traffic uses the UDP ports of 67 and 68.