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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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A Client Cannot Obtain an IP Address (the device Functions as the DHCP Server)

A Client Cannot Obtain an IP Address (the device Functions as the DHCP Server)

The device functions as a DHCP server and allocates IP addresses to clients in the same network segment or different network segments.

Common Causes

This fault is commonly caused by one of the following:

  • A fault occurs on the link between the DHCP client and the DHCP server.
  • DHCP is disabled on the device.
  • The DHCP address allocation mode is not set on an interface of the device.
  • When IP addresses are allocated from the global address pool, addresses contained in the global address pool and the IP address of the VLANIF interface are in different network segments.
  • When IP addresses are allocated from the global address pool:
    • If the client and server are located on the same network segment, all IP addresses in the global address pool and the interface IP address on the device are on different network segments.
    • If the client and server are located on different network segments and no relay agent is deployed, all IP addresses in the global address pool and the interface IP address on the relay agent are on different network segments.
  • There are no available addresses in the address pool.

Troubleshooting Flowchart

Figure 18-1 shows the troubleshooting flowchart.

Figure 18-1  Troubleshooting flowchart for the failure to allocate an IP address from the DHCP server to a client

Troubleshooting Procedure

NOTE:

Saving the results of each troubleshooting step is recommended. If you are unable to correct the fault, you will have a record of your actions to provide technical support personnel.

Procedure

  1. Check whether a fault occurs on the link between the client and the DHCP server.

    • If the client and server are on the same network segment and no relay agent is deployed, configure an IP address for the client network adapter connecting the client and the server. Ensure that the IP address of the network adapter and the interface IP address are on the same network segment. Ping the interface IP address from the client.
      • If the ping operation fails, the link is faulty. Refer to A Ping Operation Fails to rectify the link fault.
      • If the ping operation succeeds, go to step 2.
    • If the client and server are on different network segments and a relay agent is deployed, ping the links between the client and the relay agent and between the relay agent and the server.
      • If the ping operation fails, the link is faulty. Refer to A Ping Operation Fails to rectify the link fault.
      • If the ping operation succeeds, go to step 2.

  2. Check that DHCP is enabled.

    NOTE:

    If DHCP is disabled, the device does not process DHCP messages sent by the DHCP client.

    Run the display current-configuration | include dhcp enable command to check whether DHCP is enabled. By default, DHCP is disabled.

    • If no DHCP information is displayed, DHCP is disabled. Run the dhcp enable command to enable DHCP.
    • If dhcp enable is displayed, DHCP is enabled. Go to step 3.

  3. Check whether DHCP address allocation mode is set on the interface of the device.

    NOTE:

    If the DHCP address allocation mode is not set on the interface of the device, the client cannot obtain an IP address in DHCP mode.

    Run the display this command in the interface view to check whether the DHCP address allocation mode is set.

    Information Displayed Description Subsequent Operation
    dhcp select global The device allocates IP addresses to DHCP clients from the global address pool on the interface. Perform step 4.
    dhcp select interface The device allocates IP addresses to DHCP clients from the interface address pool on the interface. Perform step 5.
    No information displayed The DHCP address allocation mode is not set on the interface. Run the dhcp select global or dhcp select interface command to set the DHCP address allocation mode on the interface.

  4. Check whether addresses in the global address pool and the IP address of the interface are on the same network segment.

    1. Run the display ip pool command to check whether a global address pool has been created.
      • If a global address pool has not been created, run the ip pool ip-pool-name and network ip-address [ mask { mask | mask-length } ] commands to create a global address pool and set the range of IP addresses that can be dynamically allocated.
      • If the global address pool has been created, obtain the value of ip-pool-name. Then go to step b.
    2. Run the display ip pool name ip-pool-name command to check any IP address in the global address pool is on the same network segment as the interface IP address.
      • The client and server are located on the same network segment and no relay agent is deployed:
        • If any address in the global address pool is on a different network segment than the interface IP address on the device, run the network ip-address [ mask { mask | mask-length } ] command to reconfigure the global address pool. Ensure that all IP addresses in the address pool are on the same network segment as the interface IP address on the device.
        • If all addresses in the global address pool and the interface IP address on the device are located on the same network segment, perform step 5.
      • The client and server are located on different network segments and a relay agent is deployed:
        • If all addresses in the global address pool and the interface IP address on the relay agent are located on different network segments, run the ip address ip-address command to change the interface IP address to be on the same network segment as all addresses in the global address pool.
        • If all addresses in the global address pool and the interface IP address on the relay agent are located on the same network segment, perform step 5.

  5. Check whether the address pool contains available IP addresses.

    Run the display ip pool name ip-pool-name command to check the availability of IP addresses in the global or interface address pool.

    • If the value of Idle(Expired) is equal to 0, no IP address can be allocated from the address pool.
      • If the device has used the global address pool on the interface to allocate IP addresses to clients, re-create a global address pool where the network segment can be connected to the previous network segment but cannot overlap with the previous network segment.
      • If the device has used the interface address pool on the interface to allocate IP addresses to clients, reconfigure an IP address for the interface. This IP address and the previous IP address must be on different network segments.
    • If the value of Idle(Expired) is greater than 0, there are idle (expired) IP addresses. Go to step 6.

  6. Contact technical support personnel and provide them with the following information.

    • Results of the preceding troubleshooting procedure
    • Configuration file, log file, and alarm file of the device

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Updated: 2019-05-10

Document ID: EDOC1000079719

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