8

I have a single Cisco AP-1602 broadcasting 3 SSIDs in a small office. Some of my team are complaining about random drops in network connectivity. (Over 3 days, I've had 3 different users complain about drops every 10 minutes or so.)

What could be causing this? Are 3 SSIDs on the same channel at the same strength (because they are all from the same AP) causing interference? Are these APs built to broadcast multiple networks or was I sold a bill of goods by a reseller?

  • 2
    How many users are there total and how many have the issue? What hardware are they using? Have you performed a site survey? – some_guy_long_gone Aug 12 '13 at 14:39
  • We see a similar issue due to RF congestion. Located in New York facing an apartment building (with an AP likely in most every window) we see hundreds of broadcast SSID's. The typically successful channel hopping to find clear RF is hopeless in this environment. It happens so often our AP's would even self-reset after a period of time, thus causing clients a momentary drop. We have to hard set the channels and just live with the crowded RF. – 8None1 Sep 3 '13 at 16:53
10

There could be many causes for this, but your suspicion about the AP not being built to broadcast multiple WLANs is not one of them.

I would start by looking at this list:

  1. What version of code are you running on the AP? Upgrade to a more recent code if possible, as there may be bugs in your current code.
  2. Check for sources of interference or other usage on the channel you are using. The 1602 includes clean air express I believe, so you should be able to do this from the hardware built into the AP itself.
  3. Check the hardware that is having problems for similarities and look for problems related to the hardware (make sure their drivers are up to date). For instance, some Apple 802.11n products have issues if you disable lower 802.11n rates. Or some clients have issues with PMK caching (don't remember if Cisco has this or what it is called) if enabled. Could be re-authentication issues.
  4. Check power save configurations on the AP and clients. Could be an issue related to clients entering/leaving power save modes.
  5. Check for other configuration that could be causing the problem. Disable anything you don't need on the AP or may cause problems outside of a larger deployment. For instance, with a single AP, make sure any rogue detection or scanning is disabled. You also wouldn't need any roaming features.

Hopefully something there will get you looking in the right direction.

6

The problem seemed to be solved by two things that neither one should have changed anything:

  1. switched from WPA2 to WPA. (Yes, I know that any post 2007 device should be fine with WPA2.)
  2. reduced the number of ssid's being broadcast from 3 to 1. (Yes, as @YLearn responded, the AP should be fine with multiple SSIDs.)

So the problem is gone but the best explanation I have is, sadly, magic.

  • 4
    Make sure you are doing WPA/AES and not WPA/TKIP. If you are using TKIP, this will disable the HT (i.e. 802.11n) data rates. If you did switch to TKIP and that helped, I would again look at firmware on the AP and drivers on the client. – YLearn Sep 1 '13 at 15:47
4

Run this command on the ap:

sh controllers dot11 0 | inc dBm
sh controllers dot11 1 | inc dBm

Exactly as typed, the case matter in the piped command

I have seen hundreds of these AP's in autonomous mode that don't have their power levels set properly. this command will reveal it. Output will look like this obviously without the bullets....

BCDE-MDF-AP01#sh controllers dot11 0 | inc dBm
Configured TxPower:             22 dBm (Level Index 1)
Allowed Power Levels:           22 19 16 13 10  7  dBm
Allowed Client Power Levels:    22 19 16 13 10  7  dBm
Data Rate Sensitivity (rate, SNR dB, Contention dBm)
     Active Level              22 dBm (OFDM 22 dBm) 
     Metric unit               dBm
     HAL Per antenna Tx Power (in dBm)
     1.0 to m7t4  , 2  dBm

If you see (1.0 to m7t4 , 2 dBm) thats your issue

go to the each radio interface and enter the following

conf t
int dot11 0
power local max
power client max
int dot11 1
power local max
power client max
end
wr mem

now check the interface again and you will see and you see much higher rates:

ABCDE-MDF-AP01#show controllers dot11 0 | i dBm
Configured TxPower:             22 dBm (Level Index 1)
Allowed Power Levels:           22 19 16 13 10  7  dBm
Allowed Client Power Levels:    22 19 16 13 10  7  dBm
Data Rate Sensitivity (rate, SNR dB, Contention dBm)
        Active Level              22 dBm (OFDM 22 dBm) 
        Metric unit               dBm
        HAL Per antenna Tx Power (in dBm)
     1.0 to m6-2  , 17  dBm
    m7-2 to m7-2  , 15  dBm
    m8-2 to m13-2 , 17  dBm
   m14-2 to m14-2 , 16  dBm
   m15-2 to m15-2 , 15  dBm
   m16-2 to m21-2 , 17  dBm
   m22-2 to m22-2 , 15  dBm
   m23-2 to m23-2 , 14  dBm
    m0-4 to m6-4  , 17  dBm
  Output suppressed...

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