[WLAN]Q&A: How Can I Know Whether an AP Has Obtained an IP Address? If an AP Fails to Obtain an IP Address,How Do I Troubleshoot the Fault?

A CAPWAP tunnel can be established between an AP and an AC only after the AP has obtained an IP address. In most cases, a DHCP server is used to assign IP addresses to APs. You can check whether an IP address is assigned to the AP on the DHCP server. You can also configure a static IP address for the AP to go online.

AP going online using a static IP address

If the AP is configured to go online using a static IP address, perform the following steps to troubleshoot the fault:

Log in to the AP, and run the display ap-address-info command to verify that the static IP address of the AP is correct and that the AP IP address, IP gateway address, and AC IP address are correct.

<AP> display ap-address-info
==============================================================
Active AP Address Info
  AP Mode     : static  //The AP goes online using a static IP address.
  Ip Address  : 20.1.1.100  //Static IP address of the AP
  Ip Version  : 4
  Mask        : 255.255.255.0  //Subnet mask of the AP IP address
  Gateway     : -  //Gateway of the AP  AC 0 ip     : 10.1.1.111  //AC IP address
  AC 1 ip     : -
  AC 2 ip     : -
  AC 3 ip     : -
--------------------------------------------------------------.

If the AP IP address is incorrect, run the ap-address mode dhcp command in the system view to change the IP address obtaining mode to DHCP, and then restart the AP to make the configuration take effect.
```
[AP] ap-address mode dhcp 
Info: The configuration takes effect after the AP is restarted.
```
Alternatively, run the ap-address static ip-address ip-address subnet-mask command in the system view to change the static IP address of the AP, and then restart the AP to make the configuration take effect.
```
[AP] ap-address static ip-address 10.1.15.253 255.255.240.0
Info: The configuration takes effect after the AP is restarted.
```
Check whether the AP diagnosis log contains the following record: AP ip mode[static], ip version[4], ip address[], mask[], gateway[], AC ip number[], AC ip list[]. If not, the problem occurs when the AP obtains the static IP address information from the flash memory or when interface information is configured. Check the log for related error records, and rectify the fault based on the error messages.
```
[AP-diagnose] display diag-logfile buffer 
logfile configuration and contents in the buffer:
CRC : 0x4d3f9e94
LogBufLength : 25089

    ......   Jul 27 2005 19:02:37+08:00 ap-2 %WSRV/6/WSRV_INFO(D)[86]:Start capwap link:AP ip mode[dhcp], ip version[4], ip address[0x6c6c6cfe], mask[0xffffff00], gateway[0x0], AC ip number[0], AC ip list[].
    ......
```

AP going online in DHCP mode

If the DHCP server fails to assign an IP address to an AP, check whether the DHCP server and related device interfaces are correctly configured.

If the AP fails to obtain an IP address, check whether:

# Run commands on the DHCP server to check whether the AP is assigned an IP address. In this example, the AC functions as a DHCP server.

option 43 hex hex-string
option 43 sub-option 3 ascii ascii-string
option 43 sub-option 2 ip-address ip-address &<1-8>
option 43 sub-option 1 hex hex-string
The link between the AP and AC is properly connected.
The management VLAN is created on intermediate devices between the AP and AC.
All the interfaces between the AP and AC are correctly configured and allow packets of the management VLAN to pass through.
The Option 43 field is configured in the IP address pool when a Layer 3 network exists between the AP and AC. You are advised to use the option 43 sub-option 2 ip-address ip-address &<1-8> command to configure this field. In VRRP hot standby (HSB) scenarios, the virtual IP address configured as the CAPWAP source address on the AC must be specified in the Option 43 field.

You are advised to run only one of the following commands: option 43 sub-option 3 ascii ascii-string, option 43 sub-option 2 ip-address ip-address &<1-8>, and option 43 sub-option 1 hex hex-string. If you run two or three commands, only the last one takes effect.

Run the display ip pool { interface interface-pool-name | name ip-pool-name } used command to check IP address assignment. Check whether the AP has obtained an IP address based on the MAC address.

[AC6605] display ip pool interface Vlanif1219 used
  Pool-name      : Vlanif1219
  Pool-No        : 4 
  Lease          : 1 Days 0 Hours 0 Minutes
  Domain-name    : -
  DNS-server0    : -
  NBNS-server0   : -
  Netbios-type   : -
  Position       : Interface       Status           : Unlocked
  Gateway-0      : 10.1.1.2
  Network        : 10.1.0.0
  Mask           : 255.255.240.0
  VPN instance   : --
  Conflicted address recycle interval: -

 -----------------------------------------------------------------------------
         Start           End     Total  Used  Idle(Expired)  Conflict  Disable
 -----------------------------------------------------------------------------
        10.1.0.1     10.1.15.254  4093     4       4084(0)         5        0
 -----------------------------------------------------------------------------
 
  Network section :
  -----------------------------------------------------------------------
  Index              IP               MAC      Lease   Status
  -----------------------------------------------------------------------
   4085     10.1.15.246    dcd2-fc9a-c800       7375   Used
   4086     10.1.15.247    1047-80af-fbc0       7369   Used
   4087     10.1.15.248    dcd2-fcf4-6420       7929   Used
   4090     10.1.15.251    dcd2-fc22-d880       9368   Used
  -----------------------------------------------------------------------

Alternatively, run the display arp command to view all ARP mapping entries. Check whether the AP has obtained an IP address based on the MAC address. If so, run the ping command to ping the obtained IP address.

[AC6605] display arpIP ADDRESS      MAC ADDRESS     EXPIRE(M) TYPE        INTERFACE   VPN-INSTANCE
                                          VLAN/CEVLAN PVC
------------------------------------------------------------------------------
......
10.1.1.2        0200-0000-0017            I -         Vlanif121910.1.15.251     dcd2-fc22-d880  2         D-0         GE0/0/1                                          1219/-10.1.15.247     1047-80af-fbc0  16        D-0         GE0/0/1                                          1219/-10.1.15.246     dcd2-fc9a-c800  15        D-0         GE0/0/1                                          1219/-10.1.15.248     dcd2-fcf4-6420  6         D-0         GE0/0/1                                          1219/-10.1.1.219      4c1f-cc6b-c248  16        D-0         GE0/0/1

Ping the IP address mapping the MAC address. If the ping operation succeeds, the AP has obtained an IP address. Otherwise, the IP address obtained by the AP has expired or the AP fails to obtain an IP address.

[AC6605] ping 10.1.15.251
  PING 10.1.15.251: 56  data bytes, press CTRL_C to break
    Reply from 10.1.15.251: bytes=56 Sequence=1 ttl=255 time=1 ms
    Reply from 10.1.15.251: bytes=56 Sequence=2 ttl=255 time=1 ms
    Reply from 10.1.15.251: bytes=56 Sequence=3 ttl=255 time=1 ms
    Reply from 10.1.15.251: bytes=56 Sequence=4 ttl=255 time=1 ms
    Reply from 10.1.15.251: bytes=56 Sequence=5 ttl=255 time=1 ms

  --- 10.1.15.251 ping statistics ---
    5 packet(s) transmitted 
    5 packet(s) received
    0.00% packet loss 
    round-trip min/avg/max = 1/1/1 ms

If no address pool is configured, run the trace enable command to enable the full-process tracing function. The following sample output shows that the AP keeps sending DHCP Discover messages.

[AC6605] trace enable  //Enable the full-process tracing function.
[AC6605] trace object mac-address dcd2-fc22-d880  //Enter the MAC address of the object to be traced.
[BTRACE][2015/06/18 15:12:37][DHCPS][dcd2-fc22-d880]:Receives DHCP DISCOVER message from interface Vlanif1219.(chaddr=dcd2-fc22-d880, ciaddr=0.0.0.0, giaddr=0.0.0.0, serverid=0.0.0.0, VPN=-, expect leasetime=0)
[BTRACE][2015/06/18 15:12:37][DHCPS][dcd2-fc22-d880]:Gateway=10.1.1.2, mask=255.255.240.0.
[BTRACE][2015/06/18 15:12:37][DHCPS][dcd2-fc22-d880]:Get pool Vlanif1219 by gateway 10.1.1.2 and vrf 0.
[BTRACE][2015/06/18 15:12:37][AM][dcd2-fc22-d880]:Receive REQUEST message. (MacAddress=dcd2-fc22-d880, Subnet=10.1.1.2/255.255.240.0, VRF=0, ExpectLease=0, UserType=20)
[BTRACE][2015/06/18 15:12:37][AM][dcd2-fc22-d880]:Get pool Vlanif1219.
[BTRACE][2015/06/18 15:12:37][AM][dcd2-fc22-d880]:Try allocate leased ip for mac dcd2-fc22-d880.(pool:4)
[BTRACE][2015/06/18 15:12:37][AM][dcd2-fc22-d880]:Request successfully.(mac:dcd2-fc22-d880, ip:10.1.15.254, vrf:0)
[BTRACE][2015/06/18 15:12:37][AM][dcd2-fc22-d880]:Offer ip 10.1.15.254 to mac dcd2-fc22-d880. 
[BTRACE][2015/06/18 15:12:37][DHCPS][dcd2-fc22-d880]:Assigned address 10.1.15.254 for dcd2-fc22-d880.
[BTRACE][2015/06/18 15:12:37][DHCPS][dcd2-fc22-d880]:Send DHCP OFFER packet.(Chaddr=dcd2-fc22-d880, Offer IP=10.1.15.254). 
[BTRACE][2015/06/18 15:12:37][DHCPPRO][dcd2-fc22-d880]:DHCP server protocol stack ends with stop. 
[BTRACE][2015/06/18 15:12:37][DHCPPRO][dcd2-fc22-d880]:Receive DHCP packet (srcif:null orgif:null length:346 mflg:UC/BC).
[BTRACE][2015/06/18 15:12:37][DHCPPRO][dcd2-fc22-d880]:Receive DHCP OFFER message.orgif:null srcif:null L3if:null srcmac:0200-0000-0
017 dstmac:dcd2-fc22-d880 vsi:- vlan:1219/0 srcip:10.1.1.2 dstip:10.1.15.254 VPN:- src-port:67 dst-port:68 msgtype:BOOT-REPLY dhcp m
sgtype:DHCP OFFER bflag:uc chaddr:dcd2-fc22-d880 ciaddr:0.0.0.0 reqip:0.0.0.0 giaddr:0.0.0.0 serverid:10.1.1.2

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