In a small office where I set up the network, we recently started to experience WAN problems on the (V)DSL line. Specifically, up to three times per day the upload link breaks down to almost zero resulting in problems with any activities needing upload bandwith (e.g. sending email attachments). A simple reboot of the DSL modem suffices to solve the problem, the upload link immediately comes back again.

The telco technician came to check the connections and stated that there are quality issues with the house connection line. Literally, he said something about 1200 FEC and 300 CRC errors in 10 minutes of measuring (not that these numbers would mean much to me).

The internet provider will send me a replacement for the modem just to rule it out as an error source. I think that's prudent, after all we did not have any connection issues in more than 10 years. On the other hand, the modem we have is only two years old and also never showed any problems until two weeks ago when this started.

Now to my actual question: about 4 weeks ago, i.e. 2 weeks before we started experiencing the described issues, I replaced the Firewall that does the pppoe dialing.

Considering that a reboot of the DSL modem (router in bridge mode) solves the issue each time, is it theoretically possible that the Firewall behind the modem is somehow responsible for the break down of the upload link?

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it.
    – Ron Maupin
    Aug 7, 2017 at 16:44

1 Answer 1


It is highly unlikely that the firewall is to blame. The most likely cause is the wiring as the technician explained. You should hire a cable installer to replace or repair the bad wiring, test, give you the test results, and guarantee his work.

  • Thanks. We wouldn't be directly involved in a repair as the office is just rented and the problem seems to be with the building connection. I really just want to rule out that it's the firewall as this is where my responsibility starts. My worry was that we didn't have any such issues before, ever, and now all of a sudden they started. Just 2 weeks after I replaced the firewall. Logic tells me it can't be the firewall but better to get confirmation.
    – vic
    Dec 24, 2015 at 17:02
  • 1
    You can have someone test and re-terminate the connections. It may be as simple as having a tech switch to a different pair. You want to do as much as you can so that you can get tests and test results.
    – Ron Maupin
    Dec 24, 2015 at 17:04

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