Spotty Internet Connection

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How do you IT guys diagnose the problem with a spotty internet connection?

Just spent an hour on the phone with TWC/Spectrum. Of course they don’t see anything wrong with their service.

They send me to The first attempt, the page didn’t fully load, the second attempt, the page didn’t load at all, the third attempt, it loaded.

On a 20/2MB line I get 24.83/2.47MB. The speed is better than what I’m paying for but its spotty.

Lately I have been getting slow and partial page loads, server not found, server timed out, etc.. Get knocked off SSH when accessing my home server from work, etc. Its not the work connection because I don’t have problems accessing other sites, just here at home and my home server.

Is there any kind of utility to check for failing hardware?


14 thoughts on - Spotty Internet Connection

  • I have the exact same problems from time to time via Comcast. Mine comes and goes, and lately it hasn’t been too bad. But when it comes, it’s down for very small amounts of time, maybe 30-90 seconds, which is just long enough to be annoying, and make the service unusable.

    When it was really bad (intermittent dropouts as described above, almost every night during prime time, usually for several hours at a time) I wrote a program to do constant pings to several servers at once. If you’re interested, I’ll see if I can find that script. But, conceptually, it ran concurrent pings to several sites, and kept some stats on drops longer than some threshold. Some tips on a program like this: use IP addresses, rather than hostnames, because ultimately using a hostname implicitly does a DNS lookup, which likely requires Internet service to work. I also did several servers at once, so I
    could prove it wasn’t just the one site I was pinging. Included in the list of servers was also the nexthop device beyond my house
    (presumably Comcast’s own router). Use traceroute to figure out network paths.

    After running this for a while—before I called them with the evidence—the problem magically cleared up, and since then it’s been infrequent enough that I haven’t felt the need to fire up the script again. When it comes to residential Internet, I am quite cynical towards monopoly ISPs like Comcast… so maybe they saw the constant pings and knew I was building a solid case and fixed the problem. Or maybe enough people in my area complained of similar problems and they actually felt uncharacteristically caring for a second.

    I haven’t been there in a while, but in the past, I’ve gotten a lot of utility out of the DSLReports Forums[1]. There are private forums that will put you in direct contact with technical people at your ISP. It can sometimes be a good way to side-step the general customer service hotline and get in touch with an actual engineer rather than a script reader. Maybe not, but worst-case you’re only out some time. Also, you might post this same question to one of the public forums over there, as there seems to be lots of knowledgeable/helpful people hanging out there. (Despite the name, it’s not only about DSL, but consumer ISPs in general.)


    Good luck, let us know if you come up with any decent resolution!

  • All depends where and what the fault is.

    You can use wireshark to check for duplicate acknowledgements and retransmissions, that’s low hanging fruit.

    Two recent issues I found that manifested in miserable browsing speed where poor dns resolution speed (many tools exist to determine your optimal forwarders or if you using the root hints it might expose this is a less than optimal configuration) made for long pauses and a bad cable for a user. The cable worked, and on the lan the retries made it seem like there wasn’t problem. Over the wan, the retries made everything painfully slow.

  • for If it ran than rather several pinging. house evidence—the to Comcast… second. utility out in reader. in

    Thanks for the info.

    I’ve seen that site before so I might check it out.

    My router/modem has a log. Its loaded with errors I can’t interpret. I
    googled a portion of it and landed on TWC forums.

    Missing BP Configuration Setting TLV

    Didn’t see much of an answer.

    Hopefully it’s a temporary thing as it just started. I don’t think it’s a problem on my end, maybe, but doubt it. I’ll give it another day or so.


  • a less user. wasn’t


    My first thought it might be a dns issue. I may change to googles dns servers and see if things improve.

    This just started in the last couple days. I know TWC and Charter are merging, but this is irritating.

    I’ll check out wireshark.

  • Hi,

    What kind of cable modem/gateway do you have? Just wondering because my 12 year old Toshiba finally crapped out and Spectrum gave me a new one. Its and ARRIS TG1682G and it only gives me a private IP not like the old one which gave me the public IP so I can’t SSH to home from work anymore, so I am wondering how you do it?

    Thanks, Steve

  • Another thing to check is the wiring to the house. If this is a cable company, it is likely that the cable to the cable modem splits off to the TV(s). Make sure there are not any unterminated co-ax cable which used to go to a TV. Make sure the cable outside the house is not damaged. The cable company can test for bad cable at your location. They may charge for this. You could get a length of co-ax and swap it in in various places to see if the problems go away.

  • for Comcast/Xfinity, I’m using a Arris SB6183 that I got at Costco.
    this is a simple modem/bridge, so /my/ router behind it gets the public IP.

    I have a spare SB6121, which is DOCSIS 3.0 up to about 130Mbps max (my current internet is around 180Mbps). I’d sell this for $30 + S&H, contact me off list.

  • if you have multiple splitters, make sure the cable modem is on the
    ‘first’ one, and that splitter is a high grade 2-way one. Make sure all cable is high grade RG6 quad shield and not older RG59 or whatever.

  • Note that some residential ISPs may not offer “naked” Internet, and/or won’t allow you to bring your own device (BYOD). At least in my area, there are only two options for residential Internet; cable-based via Comcast, and DSL-based via AT&T. I used to routinely switch back and forth between the two, to play them against each other for the best rates. However, I had to give up on AT&T because they stopped offering a “naked” service. That is, when I was using them, I had the most basic DSL modem, that literally did nothing except provide me with a public Internet IP and the service. Last I talked to them, I
    could only use their service with their fancy all-in-one devices, that are both a DSL modem and gateway/router/wireless AP. I already have all that infrastructure in my house, and I trust my ability to manage it more than I trust the blackbox firmware that AT&T provides.

    Going from memory, that all-in-one DSL service did give me a public IP, but the device itself implemented NATing, so it looked like I was getting a private IP. There *may* have been a way to remove most of the functionality of the all-in-one device (“DMZ mode” or something like that); it’s been discussed pretty heavily on the DSLReports Forums. (But, either way, even ignoring the technical grievances with their service, AT&T’s prices are higher and speed tiers lower than Comcast’s.)

    TL;DR: (1) some ISPs may not allow BYOD; (2) if it looks like your ISP
    is giving you a private IP, dig a little deeper, it could simply appear that way due to the way the ISP configures the assigned device.

  • I’ve heard (don’t remember where) that typical latency for cable network providers (which comcast is) is [much?] higher than latency for DSL, even though overall data throughput may be higher for cable than for DSL. This probably is soooo outdated (if at all true). Does somebody knows the truth and could shed some light onto what is better…

    Thanks in advance!


    Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247

  • my cable modem here in santa cruz gives me 10-15mS pings to various servers in Silicon Valley. Thats about as good as it gets and is comparable to my DSL.

  • Thanks to all that replied. I had ran nmap against from the private side and saw it had a service listening on port 80, so I pointed my browser at it and a webpage came up. I looked like it was for setting up the “Wireless” because that is what the menu button said, so I initially didn’t investigate it until after I had sent my previous message. Turns out it gives you full access to setting up port forwarding, DMZ, firewall, etc. So it looks like I can use DMZ mode an be in business.

    Regards, Steve

    PS Brighthouse/Spectrum in my area lets you BYOD from a pretty large list they have certified on their network.

  • I have the same TWC/Charter provider. Also bought a SB66141 a few years back to stop paying them.


    Gets to the web interface and I go to signals page

    And make daily snapshots of that. When there’s a big change in power levels, uncorrectable codewords, or even a huge jump in correctable codewords, I know trouble is coming.

    When you call for support, ask for level 3 support three times and they
    *have* to connect you w/folks at the center that have more resources and knowledge.

    As an aid, I’ve used traceroute to identify where the problem seems to manifest, based on round-trip times, and ping. Scripted to fire off every 90 seconds so I can see change over time.

    Who you get at level 3 can make a difference. Some are lazy (e.g. latest down 7 times in the A.M. and they couldn’t tell me mtce was being done).

    N.B. My unit is modem only as I run it to IPCop and into my
    “homegroan.firewall” built by me LAN with switches.

    TWC/Charter seems to be migrating to the old sucky TWC, IMHO.

    HTH, Bill