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Remotely, how to passively speculate the missing antennas on AP.

Saravanan Lakshmanan
Cisco Employee
Cisco Employee

on ‎10-23-2015 10:52 PM


Remotely, how to manually speculate if all the 5ghz antennas are missing on single-band AP(missing, damaged, loose connection, mixed - 2.4 instead of 5ghz, incorrect model antenna....) using factors - RF neighbor AP and compare data from the nearby/adjacent APs.

This technique not applicable on below conditions:-
#High-density deployment.
#Isolated AP.
#Fully covered inventory.
#AP Radio hard down or hung.

Use case: It is mandatory to make sure 5ghz Antennas are present on the AP on a voice enabled wireless network were the preferred band is 5ghz radio OR high channel utilization witnessed on 2.4ghz radio. Within a group of APs, if 2.4ghz radio down there is always nearby AP to cover that due to better range on 2.4ghz compared to 5ghz.  Also, this logic works well on 5ghz Vs 2.4ghz due to poor 5ghz range.

Business case: Avoid sending technician onsite multiple times, Predict the Antenna failure and dispatch antenna with confidence. Alternatively, ask customer/end-user at that location to send the picture of particular AP/Antenna.

Taking 5ghz Antenna as example, below factors should guide us to predict the Antenna absence on AP when client's wlan is preferred/locked with 5ghz only.

#To begin with, Make sure the AP radio in question is admin enabled and operation sate UP. (If not check the "false positives:" section below.)
#5ghz radio showing max power level ie., 1. [It is also possible when it is isolated AP OR TPC not meeting the requirement for AP]
#No AP neighbor or few neighbors showing very low rssi and snr(even though there is another AP within few feet). [Need additional AP here OR It is also possible when it is isolated AP]
#None of the 5ghz channel showing detected interference. [It is also possible when it is isolated AP]
#No voice client(details attached below) activity found on 5ghz counters ever since this AP is installed, if voice clients used and expected to connect on this AP.                                                                                                            

#No wireless client activity found since the AP is UP(Use prime to find out, if available).
#Specific 802.11 counter showing zero or very low counts when compared with its neighbors on 5ghz radio - Tx failed count, Multiple Retry count, ACK failure count.(Under Monitor tab we can see these parameters, Use 802.11 counter prime report). It is the most important factor to check and co-relate with the above data collected to confirm the issue with all the connected Antenna, the result would be different if only one out of 3 or 4 antennas are present and OR only couple are damaged.

#Prime heatmap could be used but it is theorticial prediction and not acurate output at the surface level.

Alternatively, other manual methods can be used, it require person on-site:-

#On AP, debug the received probes on both bands, probably can't see 5ghz client. (see below)

#Show client detail showing bad RSSI and SnR.
#On AP in question, Use AP-group with 5ghz only enabled on a test wlan.

#lock WLAN to 5ghz only, Clients right under the AP gets very poor RSSI and SnR or it will connect to good AP that is far away.

#Suggest AP visual inspection on suspected AP.

#Try free wifi analyzer or Airmagnet site survey tool. Get screenshot
https://www.acrylicwifi.com/en/wlan-software/wlan-scanner-acrylic-wifi-free/download-wifi-scanner-windows/

Eliminate false positives:-
#AP's show log and more event.log shouldn't show continous radio resets because it points to different issue.
#To avoid loosing data, Gather all the above info before power cycling the AP. Power cycle the AP to be sure that the Radio is not hung.
#Check if AP is getting enough power via PoE to fire the radios.
#Run TDR to flag ethernet cable issues. AP not getting sufficient power due to poor cabling, then one or both of the radios would not come up properly.

****

(4622.wlc) >show ap stats 802.11a 4622_A76_AP6

Number Of Slots.................................. 2 
AP Name.......................................... ST4622_A76_AP6
MAC Address...................................... e8:b7:48:99:d3:52
Radio Type....................................... RADIO_TYPE_80211a
Stats Information
  Number of Users................................ 0
  TxFragmentCount................................ 346981
  MulticastTxFrameCnt............................ 346981
  FailedCount.................................... 0    ====> ZERO
  RetryCount..................................... 346981
  MultipleRetryCount............................. 0    ====> ZERO
  FrameDuplicateCount............................ 0
  RtsSuccessCount................................ 0
  RtsFailureCount................................ 0
  AckFailureCount................................ 0    ====> ZERO
  RxIncompleteFragment........................... 0
  MulticastRxFrameCnt............................ 0
  FcsErrorCount.................................. 3069117
  TxFrameCount................................... 346981
  WepUndecryptableCount.......................... 0
  TxFramesDropped................................ 0
Call Admission Control (CAC) Stats
  Voice Bandwidth in use(% of config bw)......... 0
    Total channel MT free........................ 0
    Total voice MT free.......................... 0
    Na Direct.................................... 0
    Na Roam...................................... 0
  Video Bandwidth in use(% of config bw)......... 0
  Total BW in use for Voice(%)................... 0
  Total BW in use for SIP Preferred call(%)...... 0
WMM TSPEC CAC Call Stats 
  Total num of voice calls in progress........... 0
  Num of roaming voice calls in progress......... 0    
  Total Num of voice calls since AP joined....... 0    ====> ZERO (nothing to report)
  Total Num of roaming calls since AP joined..... 0    ====> ZERO (nothing to report)
  Total Num of exp bw requests received.......... 0
  Total Num of exp bw requests admitted.......... 0
  Num of voice calls rejected since AP joined.... 0
  Num of roam calls rejected since AP joined..... 0
  Num of calls rejected due to insufficent bw.... 0
  Num of calls rejected due to invalid params.... 0
  Num of calls rejected due to PHY rate.......... 0
  Num of calls rejected due to QoS policy........ 0

Check the specific AP:

(4622.wlc) >show ap auto-rf 802.11a 4622_A76_AP6

  Interference Information
    Interference Profile......................... PASSED
    Channel 34................................... -128 dBm @  0 % busy ==> All channels are 0% busy.
    Channel 36................................... -128 dBm @  0 % busy
    Channel 38................................... -128 dBm @  0 % busy
    Channel 40................................... -128 dBm @  0 % busy
    Channel 42................................... -128 dBm @  0 % busy
    Channel 44................................... -128 dBm @  0 % busy
    Channel 46................................... -128 dBm @  0 % busy
    Channel 48................................... -128 dBm @  0 % busy
    Channel 52................................... -128 dBm @  0 % busy
    Channel 56................................... -128 dBm @  0 % busy
    Channel 60................................... -128 dBm @  0 % busy
    Channel 64................................... -128 dBm @  0 % busy
    Channel 100.................................. -128 dBm @  0 % busy
    Channel 104.................................. -128 dBm @  0 % busy
    Channel 108.................................. -128 dBm @  0 % busy
    Channel 112.................................. -128 dBm @  0 % busy
    Channel 116.................................. -128 dBm @  0 % busy
    Channel 120.................................. -128 dBm @  0 % busy
    Channel 124.................................. -128 dBm @  0 % busy
    Channel 128.................................. -128 dBm @  0 % busy
    Channel 132.................................. -128 dBm @  0 % busy
    Channel 136.................................. -128 dBm @  0 % busy
    Channel 140.................................. -128 dBm @  0 % busy
    Channel 149.................................. -128 dBm @  0 % busy
    Channel 153.................................. -128 dBm @  0 % busy
    Channel 157.................................. -128 dBm @  0 % busy
    Channel 161.................................. -128 dBm @  0 % busy
    Channel 165.................................. -128 dBm @  0 % busy

Nearby APs             ====> No APs to list.
  Radar Information

 

4622_A76_AP6#show capwap rm neighbor-list 

 Neighbor List - Dot11[0]
=================================

Neighbor[0] : 04c5.a467.1130   -75 dBm
Neighbor[1] : 04c5.a4c3.fe70   -87 dBm
Neighbor[2] : 04c5.a4c3.fcb0   -89 dBm
Neighbor[3] : 04c5.a4c3.e7b0   -87 dBm
Neighbor[4] : 44e4.d93e.bc00   -79 dBm
Neighbor[5] : 44e4.d9ab.4c00   -90 dBm
Neighbor[6] : 04c5.a48c.04c0   -83 dBm
Neighbor[7] : 04c5.a4c3.cf80   -65 dBm
Neighbor[8] : 44e4.d9ab.45f0   -77 dBm
Neighbor[9] : 04c5.a408.a710   -77 dBm
Neighbor[10] : 04c5.a467.1c50   -63 dBm
Neighbor[11] : 04c5.a48c.0910   -89 dBm
Neighbor[12] : 44e4.d9ab.4ae0   -76 dBm
Neighbor[13] : 44e4.d9ab.47a0   -86 dBm
Neighbor[14] : 44e4.d9ab.3e60   -81 dBm
Neighbor[15] : 44e4.d9ab.4a20   -89 dBm
Neighbor[16] : 44e4.d9ab.4820   -91 dBm

 Neighbor List - Dot11[1]
=================================   

                                                                  ====> No APs to list.

4622_A76_AP6#

****
4622_A76_AP6#debug dot11 rxprobe
dot11 RX Probe debugging is on
4622_A76_AP6#
4622_A76_AP6#term mon
4622_A76_AP6#
*Oct 23 23:25:04.811: ToCtrl: 00021A, 001, -11b, ffff.ffff.ffff, 0040.176b.6ab6 SSID: orange12
*Oct 23 23:25:04.811: ToCtrl: 00021B, 001, -11b, ffff.ffff.ffff, 0040.176b.6ab6 SSID: NULL
*Oct 23 23:25:08.130: ToCtrl: 0006C5, 001, -11b, ffff.ffff.ffff, 0040.176b.6ab6 SSID: orange12
*Oct 23 23:25:10.398: ToCtrl: 00076E, 001, -11b, ffff.ffff.ffff, 0026.b011.ed36 SSID: NULL
*Oct 23 23:25:10.455: ToCtrl: 0007A6, 001, -11b, ffff.ffff.ffff, 0026.b011.ed36 SSID: NULL
*Oct 23 23:25:17.756: ToCtrl: 000386, 001, -11b, ffff.ffff.ffff, 6002.b492.dbdd SSID: NULL
*Oct 23 23:25:20.175: ToCtrl: 0004C4, 001, -11b, ffff.ffff.ffff, d49a.2014.b8ac SSID: Home1
*Oct 23 23:25:26.526: ToCtrl: 000505, 001, -11b, ffff.ffff.ffff, 344d.f787.62d0 SSID: attwifi
*Oct 23 23:25:26.542: ToCtrl: 000514, 001, -11b, ffff.ffff.ffff, 344d.f787.62d0 SSID: attwifi
*Oct 23 23:25:35.501: ToCtrl: 000749, 001, -11b, ffff.ffff.ffff, 2c9e.fca5.04c0 SSID: BJNPSETUP
*Oct 23 23:25:35.501: ToCtrl: 00074A, 001, -11b, ffff.ffff.ffff, 2c9e.fca5.04c0 SSID: BJNPSETUP
*Oct 23 23:25:42.900: ToCtrl: 00038C, 001, -11b, ffff.ffff.ffff, 00c6.10e5.8ef1 SSID: CARE4U
*Oct 23 23:25:42.906: ToCtrl: 000390, 001, -11b, ffff.ffff.ffff, 00c6.10e5.8ef1 SSID: Hard Rock Hotel Punta Cana WIFI
*Oct 23 23:25:42.906: ToCtrl: 000391, 001, -11b, ffff.ffff.ffff, 00c6.10e5.8ef1 SSID: Onelife Fitness Public WiFi
*Oct 23 23:25:42.909: ToCtrl: 000395, 001, -11b, ffff.ffff.ffff, 00c6.10e5.8ef1 SSID: SuiteWIFI-2
*Oct 23 23:25:42.912: ToCtrl: 000396, 001, -11b, ffff.ffff.ffff, 00c6.10e5.8ef1 SSID: lifeisgood
*Oct 23 23:25:45.463: ToCtrl: 000555, 001, -11b, ffff.ffff.ffff, fcdb.b373.463a SSID: NULL
*Oct 23 23:25:45.504: ToCtrl: 00057D, 001, -11b, ffff.ffff.ffff, fcdb.b373.463a SSID: NULL
*Oct 23 23:25:48.357: ToCtrl: 000063, 001, -11b, ffff.ffff.ffff, fcdb.b318.f47b SSID: Plaza-Music
*Oct 23 23:25:48.999: ToCtrl: 0002D4, 001, -11b, ffff.ffff.ffff, 344d.f787.62d0 SSID: attwifi
*Oct 23 23:25:49.015: ToCtrl: 0002E3, 001, -11b, ffff.ffff.ffff, 344d.f787.62d0 SSID: attwifi
*Oct 23 23:25:49.839: ToCtrl: 00060A, 001, -11b, ffff.ffff.ffff, 344d.f787.62d0 SSID: attwifi
*Oct 23 23:25:49.855: ToCtrl: 000619, 001, -11b, ffff.ffff.ffff, 344d.f787.62d0 SSID: attwifi
*Oct 23 23:26:01.396: ToCtrl: 00022B, 001, -11b, ffff.ffff.ffff, 0040.176b.3e8c SSID: orange12
*Oct 23 23:26:01.396: ToCtrl: 00022B, 001, -11b, ffff.ffff.ffff, 0040.176b.3e8c SSID: NULL
*Oct 23 23:26:03.853: ToCtrl: 00038C, 001, -11b, ffff.ffff.ffff, 529c.c35f.cc38 SSID: NULL
*Oct 23 23:26:03.907: ToCtrl: 0003C3, 001, -11b, ffff.ffff.ffff, 529c.c35f.cc38 SSID: NULL
*Oct 23 23:26:05.788: ToCtrl: 0002F1, 001, -11b, ffff.ffff.ffff, d49a.2014.b8ac SSID: Home1
*Oct 23 23:26:06.018: ToCtrl: 0003D0, 001, -11b, ffff.ffff.ffff, 0040.176b.24f6 SSID: NULL

 

****

4622_A76_AP6#show int dot11 1 statist
        DOT11 Statistics (Cumulative Total/Last 5 Seconds):
RECEIVER                               TRANSMITTER
Host Rx K Bytes:       1108 / 0        Host Tx K Bytes:          2645 / 11
Unicasts Rx:              0 / 0        Unicasts Tx:                 0 / 0
Unicasts to host:         0 / 0        Unicasts by host:            0 / 0
Broadcasts Rx:           15 / 0        Broadcasts Tx:          101125 / 333
Beacons Rx:              15 / 0        Beacons Tx:             101125 / 333
Broadcasts to host:      15 / 0        Broadcasts by host:          0 / 0

===> Very low count on Broadcasts Rx, Beacons Rx & Broadcasts to host.

4622_A76_AP6#show int dot11 0 statist
        DOT11 Statistics (Cumulative Total/Last 5 Seconds):
RECEIVER                               TRANSMITTER
Host Rx K Bytes:    1686988 / 17171    Host Tx K Bytes:           954 / 0
Unicasts Rx:              0 / 0        Unicasts Tx:                 0 / 0
Unicasts to host:         0 / 0        Unicasts by host:            0 / 0
Broadcasts Rx:       155913 / 468      Broadcasts Tx:          102153 / 334
Beacons Rx:          155416 / 466      Beacons Tx:             102153 / 334
Broadcasts to host:  155913 / 468      Broadcasts by host:          0 / 0

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