Case Study: A STA Prefers Channels 1 to 11 and Does Not Associate with or Roam to the Nearest AP

Symptom

As shown in Figure 6-4e, a STA proactively associates with AP13 but does not associate with or roam to the nearest AP2.

Figure 6-4 STA associating with a remote AP

Relevant Alarms and Logs

None

Cause Analysis

The wireless network adapter used by a STA complies with only the 802.11b/g/n protocol on the 2.4 GHz frequency band and therefore prefers channels 1 to 11 instead of channel 13. That is, when the STA receives signals of SSIDs on channel 13 and other channels, the STA is more likely to connect to an AP that does not use channel 13.

Procedure

1. Check the STA onboarding process using the station-trace function, and analyze information about the AP with which the STA proactively associates upon its first access to the WLAN. It is found that the STA proactively associates with AP13 instead of the nearest AP2.

   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4] [WSTA] Receive STA (Re)associate request message.Local:1, AP:13, Radio:0, Wlan:1, Type(1:assoc, 2:reassoc):2, Pmk ID:0, Wapi IE:22, Bk ID Num:0, SFN Flag:0, Ability:3, 2.4G CHs:0, 5G CHs:0.FT Roam:0, FT Access:0, Rssi:-67, Old Ap Mac:0000-0000-0000, Auth Type:5 UniCipher:5 MultiCipher:5. Src vcpuId:2. Message:139, Elem:127, Total:135, Fix:88, Ext num:1, Ext Len:27, AGV:0, Assoc duration time:22434, AccessId:249276772
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Get sta cfg info VapProfileID:5, VlanId:90, IsBoundVlanPool:0, HacServiceVlanInPool:0, MaxUserNumber:64, VlanMobilityGroupId:1, HomeAgent:0, Fordward:1 Bssid:xxxx-xxxx-xxxx, ssid:hbhc-office, Ap mac:xxxx-xxxx-xxxx, Ap name:xxx, AC IP:x.x.x.x, IsDot1xOrWapi:1, Is Ppsk:0, l3 switch:0
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process STA associate request message:(ApId:13 RadioId:0 WlanId:1 EssId:5 Assoc Type(1:Assoc,2:Reassoc):2 Vlan:90, Type:3093, Max num:64).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4]Delete from delay hash table, state:3, code:0
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4]Layer 3 roam check(pool:0, hac group:1, assoc group:1, hac vlan:90, assoc vlan:90, layer3:0
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Begin to process STA associate request message of different VAP.
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Update sta data roam info (Assoc HAP(xxxx-xxxx-xxxx),HAP(xxxx-xxxx-xxxx), ap roam:0, layer 3 roam:0)
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Update sta data roam info:MgIP: 0.0.0.0, Ap2AcIP:192.168.95.253
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Send STA associate response message. (FT access:0, FT roam:0, Flag:0, loacl:1, Type:5)
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Send STA associate response message. (Ap:13, Radio:0, WlanId:1, Type:0, Code:0, Len:446, OpType:3, Flag:0, Detect:1)
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Send STA roam associate and add sta request(code:65534,sendLen:446,pvtLen:36,pvtAddLen:26),Pvt(x-x-x,ap:13,radio:0,wlan:1,ret:0).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Send STA associate Response message and add sta request (Type:3093, Status Code:65534, Code:0).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] End to process STA associate request message of different VAP(Code:0).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process STA associate request message (Rt:0).
   [BTRACE][2021/06/28 15:37:39][512][WLAN_AC][x-x-x]:[Process:2][WSTA] Send STA Assoc add sta respone (ap:13, radio:0, wlan:1, addsta len:26, ret :0).
   [BTRACE][2021/06/28 15:37:39][512][WLAN_AC][x-x-x]:[Process:2][WSTA] Capwap deliver message to sta process (Type:26, prim:0, len:236, fork:1024, code:0)
   [BTRACE][2021/06/28 15:37:39][512][WLAN_AC][x-x-x]:[Process:2][WSTA] Update tunnlel port (Type:2,ap:2,radio:0,wlan:1,vlan:90,mode:1,direct:1,tunnel:0,code:0)
   [BTRACE][2021/06/28 15:37:39][512][WLAN_AC][x-x-x]:[Process:2][WSTA] Notify vap vlan list(Type:2,Ap:2,radio:0,wlan:1,vlan:90)
   [BTRACE][2021/06/28 15:37:39][512][WLAN_AC][x-x-x]:[Process:2][WSTA] Update fwd elb (Type:2,ap:2,radio:0,wlan:1,vlan:90,mode:1,vap:0,code:0)
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process add STA response message (Radio:0, Wlan:1, OpType:3, TryTimes:1, code:0).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process delete STA request message(ApId:2 Radio:0 Wlan:1 Type:4).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process delete STA request message Send (ApId:2, Radio:0, Wlan:1, Type:4, Len:82, Type:4).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WADP] Send EAP authentication request message to EAPOL(Ret Code:0).srcChId:187,dstChId:209,msg:232,SrcForkId:1024,EsapForkId:1024,IfIndex:2466283533,VlanId:90,SN:4294,AccessId:249276772
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSEC] Initiate eapol start message (Interface:2466283533, Vlan:90, Sn:4294, AccessId:249276772, Code:0).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process associate successfully(State:6, Pre AP:2).
   [BTRACE][2021/06/28 15:37:39][1024][WLAN_AC][x-x-x]:[Process:4][WSTA] Process STA del response message(Len:24, Num:3, TX:45, RX:45, RSSI:4294967229).
   [BTRACE][2021/06/28 15:37:39][1024][EAPoL][x-x-x]:The ulAuthId carried in wlan request start pkt is 249276772.

2. Disable the network adapter and then restart it to attempt to connect to the WLAN. Obtain packets on the air interface. It is found that the STA does not proactively connect to AP2.

3. Check the channel and power of AP2 and AP13.
   1. Check the transmit power and channels of the APs.

      [AC] display radio ap-id 2
      CH/BW:Channel/Bandwidth
      CE:Current EIRP (dBm)
      ME:Max EIRP (dBm)
      CU:Channel utilization
      ST:Status
      WM:Working mode (normal/monitor/monitor dual-band-scan/monitor proxy dual-band-scan)
      --------------------------------------------------------------------------------------------------
      AP ID Name      RfID  Band  Type    ST  CH/BW          CE/ME   STA    CU    WM
      --------------------------------------------------------------------------------------------------
      2     xxxx      0     2.4G  11ax    on  13/20M         20/29   2      16%   normal
      2     xxxx      1     5G    11ax    on  52/40M+        28/30   1      1%    normal
      --------------------------------------------------------------------------------------------------
      Total:2
      [AC] display radio ap-id 13
      CH/BW:Channel/Bandwidth
      CE:Current EIRP (dBm)
      ME:Max EIRP (dBm)
      CU:Channel utilization
      ST:Status
      WM:Working mode (normal/monitor/monitor dual-band-scan/monitor proxy dual-band-scan)
      --------------------------------------------------------------------------------------------------
      AP ID Name      RfID  Band  Type    ST  CH/BW          CE/ME   STA    CU    WM
      --------------------------------------------------------------------------------------------------
      13    xxxx      0     2.4G  11ax    on  9/20M          12/29   0      18%   normal
      13    xxxx      1     5G    11ax    on  44/40M+        28/30   0      2%    normal
      --------------------------------------------------------------------------------------------------

   2. Run the display station sta-mac command to check the AP power reported by the STA. The command output shows that the RSSI of signals received from the nearby AP (AP2) is higher than that from AP13.

      [AC-wlan-view] display station neighbor sta-mac sta-mac
      --------------------------------------------------------------------------------------------------------------------------------
      Device MAC         Device ID   Device Name        Radio ID  Channel  Probe info(RSSI/HH:MM:SS)   11k info[RCPI/RSNI/HH:MM:SS]
      --------------------------------------------------------------------------------------------------------------------------------
      xxxx-xxxx-0410     13          AP13               0         9        -67/20:39:35                180/ - /20:23:30
      xxxx-xxxx-d990     8           AP8                0         13       -62/20:28:45                172/ - /20:34:17
      xxxx-xxxx-0490     2           AP2                0         13       -45/20:26:47                184/ - /20:25:09

   3. Run the display ap neighbor ap-id 13 command to check neighbor information of AP13. The command output shows that AP2 is a neighbor of AP13 and has a stronger RSSI than other APs.

      [AC-wlan-view] display ap neighbor ap-id 13
      Info: This operation may take a few seconds. Please wait for a moment.done.
      Radio: Radio ID of AP
      In control AP:
      ----------------------------------------------------------------------------------------------------------------------------
      Radio  AP ID  AP name    Channel  Received RSSI(dbm)  RSSI pathloss(db)  RSRP pathloss(db)  Last Update Time
      ----------------------------------------------------------------------------------------------------------------------------
      0      12     AP12       13       -76                 105                108                2021-06-27/20:36:08
      0      8      AP8        13       -44                 73                 75                 2021-06-27/20:34:59
      0      35     AP35       13       -61                 90                 91                 2021-06-27/20:35:41
      0      2      AP2        13       -57                 86                 87                 2021-06-27/20:36:08

4. Check the roaming steering operation of APs.
   1. Check the smart roaming configuration. Smart roaming is configured on the AC.

      [AC-wlan-view] rrm-profile name default
      [AC-wlan-rrm-prof-default] display this
      #
      smart-roam roam-threshold snr 35
      smart-roam quick-kickoff-threshold snr 10
      sta-load-balance dynamic disable
      #

   2. Check the STA roaming flag on the AC and AP.

      # Check STA information on the AC. The result shows that the STA is a sticky STA.

      [AC] display station sta-mac sta-mac
      Autonavigation roaming optimization support   : No
      Available for roaming                         : Yes
      Sticky station or not                         : Yes
      Aimless roaming support in sticky state       : Yes
      Station device type                           : -

      # Check the STA steering record on the AC. It is found that the STA is not steered to the target AP, that is, a blind handover occurs but the STA is still associated with AP13. That is, the STA fails to be steered.

      [AC-wlan-view] display station steer-history | include sta-mac
      S/T/A:Source/Target/Actual
      Flag:V[Voice/Video/Active STA]
      BTM success times/BTM total times:441/919
      Deauth success times/Deauth total times:0/0
      ------------------------------------------------------------------------------------------------------------------------------------
      Time                    Sta             Device(S/T/A)   Radio(S/T/A)  Rssi(S/T/A)   Reason       Move-mode  BTM_CODE  Flag  Result
      ------------------------------------------------------------------------------------------------------------------------------------
      2021-06-27/19:17:07     sta-mac         13/-/13         0/-/0         -71/-/-71     Sticky       BTM        -         -     Not Move
      2021-06-27/19:14:00     sta-mac         13/-/13         0/-/0         -71/-/-72     Sticky       BTM        -         -     Not Move

      # Run the display umac station sticky-table command on the AP. The command output shows that the STA is a sticky STA.

      [AP13-diagnose] display umac station sticky-table
      --------------------------------------------------------------------------------------------------
      STA MAC            Frequency       SNR       State       SSID
      --------------------------------------------------------------------------------------------------
      sta-mac            2.4G            29        sticky      office

   According to the preceding information, a blind handover is performed for the STA but the STA does not associate with nearest AP2. In normal cases, even if the STA does not associate with AP2 upon the first access to the WLAN, the STA will be steered to AP2 based on the smart roaming function. However, the STA associates with AP13 instead of AP2 in a timely manner.

5. Switch the channel between AP2 (channel 13) and AP13 (channel 9) to check whether the STA has a channel preference.

   [AC] wlan
   [AC-wlan-view] ap-id 2
   [AC-wlan-ap-2] radio 0
   [AC-wlan-radio-2/0] calibrate auto-channel-select disable
   [AC-wlan-radio-2/0] channel 20mhz 9
   Warning: This action may cause service interruption. Continue?[Y/N]y

   After the channel switching, it is found that the STA directly associates with AP2. This symptom persists in multiple tests. Therefore, it is suspected that the STA has a channel preference.

6. Set the calibration channel set of 2.4 GHz radios to channels 1, 6, and 11. After calibration, the WLAN access and roaming services of the STA become normal.

   [AC] wlan
   [AC-wlan-view] regulatory-domain-profile name default
   [AC-wlan-regulate-domain-default] dca-channel 2.4g channel-set 1,6,11