STA Fails to Obtain an IP Address

Troubleshooting Flowchart

Troubleshooting Procedure

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

   Check whether the STA can ping the DHCP server.

2. Check the configuration.

   Check the following items:

   • Whether DHCP is enabled on the device.
   • Whether the forwarding mode and service VLAN are correctly configured.
   • Whether the AP receives the latest configuration.
   • Whether the STA is in the blacklist or not in the whitelist, or whether the number of STAs reaches the maximum (perform this check according to section Association Failure).

3. Check whether a DHCP address pool is configured and whether the corresponding gateway exists in the IP address pool.
4. Check whether the IP addresses in the IP address pool are used up.

   [AC6605] display ip pool interface vlanif 100
     Pool-name       : Vlanif100
     Pool-No         : 0
     Lease           : -
     Domain-name     : -
     DNS-server0     : -
     NBNS-server0    : -
     Netbios-type    : -
     Position        : Interface       Status           : Unlocked
     Gateway-0       : 10.10.10.10
     Mask            : 255.255.255.0
     VPN instance    : --
    -----------------------------------------------------------------------------
       Start           End            Total  Used  Idle(Expired)  Conflict  Disable
    -----------------------------------------------------------------------------
       10.10.10.1      10.10.10.254   253    5     248(0)         0        0
    -----------------------------------------------------------------------------
   

5. Analyze logs.

   Error Code (AC Functioning as a DHCP Server)	Description
   DHCP IP POOL IS OUTFLOW	The DHCP IP address pool overflows.
   DHCP IP POOL LOCKED	The DHCP IP address pool is locked.
   NOT FIND IP POOL	Common causes are as follows: The IP address pool cannot be found on the gateway. The client has an IP address but the IP address is not in any IP address pool on the device. The IP address pool from which the client requests an IP address is not the same as that configured on the gateway. When a client attempts to go online through a two-message exchange, the IP address of the client has no matching IP address pool or the IP address pool corresponding to the client's IP address is not the same as the IP address pool configured on the gateway.
   INCORRECT REQUEST IP OR MAC	Common causes are as follows: In the Request phase of four-message exchange, the client's temporary IP address cannot be found based on its MAC address. In the Request phase of four-message exchange, the temporary address assigned to the client does not match the IP address requested by the client. In the Request phase of four-message exchange, the gateway address assigned to the client is not in the same network segment of the requested IP address. In the Request phase of four-message exchange, the DHCP server fails to assign an IP address to the client. In the Request phase of four-message exchange, the address assigned to the client does not match the IP address requested by the client. During two-message exchange, the client's address lease cannot be found. During two-message exchange, the IP address requested by the client is not the same as that assigned by the device. During two-message exchange, the client fails to apply for an IP address. During two-message exchange, the applied IP address is not the expected one.
   IP CONFLICTED	IP address conflict occurs.

6. Collect the following diagnosis information and discuss with related R&D personnel.

   The normal process for obtaining an IP address from the DHCP server is as follows:

   1. The STA sends a DHCP discovery packet.
   2. The DHCP server replies with a DHCP offer packet.
   3. The STA sends a DHCP request packet.
   4. The DHCP server replies with a DHCP ACK packet.

   If the DHCP server is deployed on the AC, you can use the trace command to trace the entire process and determine whether the fault occurs on the STA or DHCP server. If the DHCP server is not deployed on the AC and you cannot determine the DHCP step in which the fault occurs, you can capture packets or use the following diagnostic commands to collect fault information.

   • Run the debugging dhcp packet process client-mac xxxx-xxxx-xxxx all command in the diagnostic view. Then locate the fault according to the command output.
   • If the DHCP process is normal on the wired side, enable the Wi-Fi-side debugging function on the AP to determine the DHCP step in which the fault occurs.