If a RAP provisioned for 4G uplink does not come up, how do we troubleshoot ?

Aruba Employee
Aruba Employee

Environment : This article applies to Aruba Mobility Controllers running ArubaOS version with RAP provisioned to it using uplink as  4G Modem as listed Below 

  • Make sure the 4G modem used with RAP is interoperable
  • Also not all Aruba AP models support 3G/4GUSB modems. As of August 2013 the AP models that support 3G/4G uplinks are:



For RAP's newer than the list above , please refer to the Spec sheet of the RAP to find out the support for 3G/4G uplink.


Though Ethernet uplinks are very common in most deployments they are not ubiquitous. So deployments where Ethernet is not an option or deployments that require a redundant uplink can be configured to use 3G/4G USB modems as uplink.

The usual procedure is , first  we bring up the RAP on the controller using wired connection and configure the parameters on the RAP console page, and go for "connect"  to verify if the RAP comes up on the controller and then we connect the USB-modem to the RAP , Configure the USB modem parameters on the controller's provisioning page(with hishest priority for USB) and reboot the RAP. So after reboot it will come up using the USB-4G modem.

But on some occasions the RAP may Fail to come up using 4G Modem as uplink due to several reasons but not limited to :

  • Mac address of the RAP not added to the whitelist DB  in the controller
  • Incorrect Modem Provisioning Parameters
  • Lower cellular Link Priority
  • Incompatible Modem Frimware
  • Faulty 4G Modem
  • Faulty RAP
  • If the Modem is supported and still the RAP doesn't comes up , Check if the AP does show up in the “show ap bss-table” or “show ap active



If not then we need to check if the RAP3/5 is provisioned correctly and is able to establish the IPSEC/UDP 4500 session with the controller.



  • We can check the output of the command “show datapath session table | include 4500” to make sure we see 4500 sessions between the controller and the RAP being used.

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If we do not see any 4500 sessions for IPSEC on the controller from the modem, we can verify if the USB modem card is giving out an IP address by connecting it to a PC/laptop. 



  • The following two commands can be used to check if ISAKMP/IPSEC SA’s are active or not. 


(Aruba3200) # show crypto isakmp sa peer <public ip of the RAP >


(Aruba3200) # show crypto ipsec sa peer <public ip of the RAP >
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  • Check if the Mac address of the RAP is added to the whitelist DB  in the controller

  (Aruba3600)#show whitelist-db rap

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  • To view the USB modem details on the RAP, execute the following command:

show ap debug usb ap-name <ap-name>

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  • Check for correct Modem Provisioning Parameters
Every 3G/4G modem uses certain connection/device parameters to connect to the 3G/4G network. These modem parameters depend on the modem type and  service providers.  Some of the common parameters used by the modems are (not all parameters are used by all modems):

    device type
    TTY device path
    device identifier
    initialization string
    dial string
    USB user name
    USB password
  Make sure Cellular NW Preference is set to Auto , Advanced and 4G-only to use 4G network , Setting it to 3G-only will connect your modem only to 3G networks.
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  • Check for Ethernet/Cellular Link Priority on WebGUI of the controller
  • Connect the Modem to a PC to make sure that it gives an IP and takes you online

 To View a detailed system status information for an AP

Show ap debug system-status ap-name <ap-name>

For USB Modem parameters 

Accessing Console

Unfortunately, there is no console on the RAP5, so you will not be able to troubleshoot the connection. You will be able to check 'rapconsole.arubanetworks.com', when you plug in to the E1 port of your RAP; and see how the LED indicator on the 4G dongle behaves and compare it to when connecting the USB modem with a PC; the indicator will show the connection status (depending on the stick that we use...).


For other Models of RAP we can Access the RAP console to debug USB modem, you will need a special Console cable for the purpose

Press ESC ^k  which will unlock AP console
All logs will be in /tmp

look for the sapd debug logs and lte logs :


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