Connecting a CradlePoint CBA750 to a Cisco 3560 switch

Need your help.  Our company made a decision to implement a network backup that uses Verizon LTE 4G.  The setup is as follows:  On the corporate side there is a Cisco 2911 using VPN going to the Verizon private network.  On the remote side we have a series of layer 3 switches (Cisco WS-C3560X-24P-L).  On the suggestion of Verizon we purchased CradlePoint CBA750 modem/router devices. 

We need to use the Verizon connection as the backup.  The primary is Metro Ethernet going through another ISP.  When connecting the CradlePoint to the switch the link will not activate (actually receive a down/ err-disable).  I can use a PC directly to the CradlePoint Ethernet port and test successfully.

My question is does anyone have experience in connecting the CradlePoint to Cisco Switches?  I have eliminated the cable (it is straight-through)  and also made a call to both Verizon and CradlePoint (have not called Cisco as of this writing)  The CradlePoint is being set in IP Pass-through mode and is receiving its address from Verizon.  I think I have covered the basics so if anyone could lead me in the right direction I would appreciate it.  Thanks.

I've worked on this before and had a couple difficulties. First make sure the DHCP option is turned off on the CP. With your laptop, verify what IP you are getting. I ran in to an issue where Verizon was handing out an IP that wasn't an officially legitimate IP. It was something in the realm of 9.9.9.163/30. Windows didn't mind this IP, but when you look closer the subnet of the IP was 9.9.9.160/30, and the 163 address was actually a broadcast address according to subnetting rules. Not sure how or why VZ was handing that out, but I had to put in a request to have my public IP changed. This may or may not be your case.

For the Err-disable, did you see the reason for the err? "show int status err" will give you better details. Also, check the speed/duplex settings on both devices.

Here is the configuration for the Fast Ethernet Port

interface FastEthernet0/1

 switchport access vlan 140

 switchport mode access

 speed 100

 duplex full

Jun 27 12:40:46: %ILPOWER-7-DETECT: Interface Fa0/1: Power Device detected: IEEE

 PD

Jun 27 12:40:47: %ILPOWER-5-IEEE_DISCONNECT: Interface Fa0/1: PD removed

I believe that explains the port flapping.  Am I getting this error due to the CradlePoint or is the switch looking for the device to not have a power supply attached?

Thanks to all of you.  I was able to find out that the Cisco WS-C3560X-24P-S switch considered  the CradlePoint a PoE device.  Since I am using the power cord on the CradlePoint it was causing an issue with the switch.  Turned off the power on the port by using the 'power inline never' command.  The port is up now with no flapping.  I got a piece of the answers from the posts I received so thanks to the posters.