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Solved: Asus 4G-AC55U randomly going offline

by Finn Espen Gundersen on November 13th, 2016
ASUS 4G AC55U Router

This Asus 4G router can be great, if configured correctly.

It has excellent sensitivity. Previously, I needed an external (outdoors) antenna to get 3G and 4G (LTE) coverage at the cabin; but the AC55U is sensitive enough to get the same reception indoors. I have another one at a remote shooting range to provide WiFi there.

But sometimes, even with the (at writing) most recent firmware, it suddenly disconnects from the mobile provider or refuses to route traffic. At first I wrote it off as random service issues with the mobile coverage. After all, these are rural areas with weak signal. But the outages kept appearing while my cell phone worked fine.

Turns out, the firmware has a couple of problems.


Since the mobile connection is metered, I made use of the ability to notify me by SMS of approaching usage limits. To avoid overcharge fees I also set a hard limit to shut down the mobile connection.

But there is an overflow issue in the firmware, triggering the forced shut-down seemingly at random.

Extreme (wrong) data usage

Notice the Data Usage (click to enlarge).

The necessary work-around is to NOT use the Data Usage Limit feature, it has to be disabled by setting it to zero (see above screenshot).

Since then, uninterrupted operation both at the cabin and the shooting range.


If you experience the router losing connection for minutes at a time for no reason, then try pinging some random server. If ping works the chances are good the problem is the routing table.

When the mobile provider updates the IP of the router, the router often fails to update the routing table, resulting in no traffic. The routing table can be found under the menu System Administration / Routing Table. As an example, I used my operator’s smartphone APN with the dial-code *99# (see picture above). The IP would change every few hours resulting in loss of traffic for several minutes. Changing the APN to internet and no dial-code solved this issue. I am not sure if it was “solved” just by greatly reducing the frequency of IP changes, or if the lack of dial code is relevant.

In any case, rebooting the router will update the routing table.

From → Hardware

  1. HÃ¥vard permalink

    Would you not be better off with some ~10W embedded and fanless Atom box running pfSense for this? A lot more to tinker with anyway, and upgradeable with next-gen WiFi by replacing just adapter or external AP. Initial cost could also be comparable to these higher-end plastic consumer boxes.

    To the point and assuming a powercycling fixes both of the issues, a dirty but quite effective remedy would be to put a cheap electronic timer between socket and PSU, programming it to switch off for a minute every morning at 5 AM…

    Greetings from Oslo 🙂

    • Finn Espen Gundersen permalink

      pfSense is great. But the Asus box has good 4G antenna sensitivity. A random box with pfSense would need a 4G adapter with external antenna. And a lot more time to set up properly compared to an out of the box product. Sometimes tinkering is fun, sometimes you just want stuff to work.

  2. Hakim permalink


    For me the problem persist for the routing table :/
    Any other idea ?

    • Fufs permalink

      A micro controller with Wi-Fi that would power cycle the router after internet connection is lost?

  3. Finn Espen Gundersen, you are my hero. Looks like with your help i could repair the bug of my Asus.

    Thanks a lot.


  4. I tried your suggestions, but it didn’t help me. My Asus 4G-AC55U looses it’s connection at times and it won’t return until I reset the router manually. Finally I bought a Raspberry Pi and a Tellstick Duo and connected it all to a Nexa remote controlled power switch. Then I wrote a program that polls the Internet and if the connection is lost I toggle the Nexa socket.

    If someone is interested I wrote a small description of my setup on my web page:

  5. Djamel permalink

    Hello All,

    i have the same issue with the AC55U.
    I’m losing the connection often and by telnet i’m reseting the 4G DHCP.

    udhcp -u usb0 /renew

    seem that the router cannot get the new ip when the provider change it.

    not sure about the routing table. could you check with my cmd and keep me posted if it’s work.


  6. Djamel permalink

    udhcp -i usb0 /renew (sorry my bad)

  7. rhug permalink

    Nice conversation.I solved my Asus problem too

  8. Thor permalink

    I believe the 4G-AC55U became stable with the M14 MODEM firmware update: Version


  9. Andy permalink

    Thanks Finn and Thor!

    I had not relaized that i had to “manualy” update the modem part of the router. See link below

    Did speed test before and after updating from M12 to M14 and this showed an significant decreas in downlink speed and increas in uplink speed after the update despite several powercycles of router. Is this seen by others as well?

    Is there any known way of rebooting the modem part thru command line interface? The modem seems to need a powercycle to come out of its bad state. Hopefully M14 will fix issue thou…

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