Getting a C819G 4G LTE router to 4G LTE

The other day I was tasked with troubleshooting a Cisco 819G 4G router, as the customer was getting poor signal at its location. Being a newbie in the world of Network Engineering, I had never worked with one before. So when the opportunity to debug one came, I made the decision to spend some time looking into it.

Ten of these routers were bought for a customer, who required internet connectivity in remote locations, where it wasn’t possible to install a fixed line.

Saying that I had never worked with a 819G router before, is a bit of a lie. After the consultant in charge of this project left the company, I took over with configuring the routers. He had prepared a template, which was ready to be loaded on to the router. So it was easy-peasy preparing the routers when the customer was ready for the next. Or so it seemed…

The Cisco 819G is a small Machine-2-Machine Intergrated Services router, which can – well – route. What is special about this little box is, it contains a 4G LTE modem. So with a mobile broadband backhaul it can either serve as a ISR with 4G LTE redundancy, or it can route wirelessly over the 4G network. In this particular scenario, the latter is employed.

One thing to notice is that the 4G connection does not go up immediately, but instead will only go up when traffic is generated on the interface. A couple of pings should suffice. But if you are setting up at VPN for the connection, expect som amount of pings to fail before the VPN tunnel is established. I’ve learned that 100-200 repetitions (ping rep 100) should be enough.

Foeh Mannay has an excellent blog-post on configuring a MWE for the cellular modem of the router.

In order to get the router to initialize the call, it is necessary to create the APN profile. This must be done with the Cellular interface in a shutted state. For TDC in Denmark, the APN name is internet.

interface cellular 0
cellular 0 lte profile create 1 internet none
configure t
interface cellular 0
no shutdown

If you for some reason what to force LTE, you can do so by entering

conf# interface cellular 0
conf# shutdown
conf# ^Z
# controller cellular 0 lte tech {lte|auto}
conf# interface cellular 0
conf# no shutdown

To get some LTE relevant statistics, use

# sh controller cellular 0 {radio|network}

This gives a status on radio reception and network preferences, respectively. The latter should show you whether or not you are using LTE og maybe legacy network. With the former you can check things like RSSI, RSRQ SNR, and so on.

As a last resort if you are still not getting LTE reception – call the ISP, and check to see if your subscription plan allows 4G LTE.. It may seem obvious, but it took me a full day of WTFs before I got this epiphany.

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