Odd network issue, Mac seemed to cause it

Discussion in 'Mac Basics and Help' started by hallux, Jul 9, 2013.

  1. hallux, Jul 9, 2013
    Last edited: Jul 9, 2013

    hallux macrumors 68030


    Apr 25, 2012
    This will be lengthy but thorough.

    Background: I've been having intermittent internet drops for the last 4 months, seemed to start with the installation of a modem I bought so I could save the $5/month charge to use an ISP-supplied modem. The router I'd prefer to use is a Netgear WNDR-3700, my "backup" and the one that I've been using for a week to test a theory is a Linksys WRT54G-L with DD-WRT on it.

    Yesterday, all seemed well when I got home from work, everything seemed to work fine. I went out for a bit, came back and all went down the tubes. I had poor connectivity, if at all. No changes were made yesterday, except when I started troubleshooting. I swapped to the Netgear thinking maybe I was getting interference on the 2.4 Ghz band, while I could use 5 Ghz on the Netgear (I can pick up almost a dozen other wireless networks when I scan). I first noticed the issue while trying to upload a photo using iPhoto.

    I try connecting directly to the modem, minimal change, so I call my ISP, spend an hour on the phone with them and get nowhere. While doing this, I start seeing a pattern, when my Mac is plugged into the modem directly, I still have issues. When I plug in my self-built Windows desktop everything is perfectly fine.

    I shut EVERY device off (iPad, Android tablet, HP printer, desktop), unplug the modem and the router (the Linksys at this point), plug in the modem and then once that booted the router. Once the router was up I booted my desktop, all was good (start running speed tests at speedtest.net after each device). Turned the printer on, fine. Android tablet, fine. iPad, fine. Booted the Mac, down the tubes instantly. When I log in to the Mac, Chrome comes up automatically (haven't figured this out either, I've removed it from login items), none of my tabs that load automatically can connect. I have CrashPlan for backup, that can't connect, Google Drive can't connect. I start killing the extraneous processes that use network (Drive, CP) and still can't connect and see high outbound network usage.

    At this point it's 11:30 at night, I close the lid on the Mac and go to bed. I woke up this morning and it was like there was never a problem. I have no idea what's going on, the Windows convert in me wants to just wipe it and start over but there HAS to be a better way. I used nettop in terminal but didn't see anything overly disturbing.

    Thanks for reading, hoping someone here has ideas.

    Update, after thinking about it, I installed 2 updates to the Mac yesterday, one was for RAW compatibility, the other was a security update. I wonder if the security update caused this.
  2. chown33, Jul 9, 2013
    Last edited: Jul 9, 2013

    chown33 macrumors 604

    Aug 9, 2009
    1. Did you try switching modems? If the problems started with the modem change, why not switch modems? Do you have a spare one of a different model? Do you know someone who can lend you a different model?

    2. You haven't identified the new modem.

    3. You haven't identified the earlier modem, which apparently worked.

    4. You haven't said whether you had any problems at all with the earlier modem, nor what router(s) you used with it.

    Which channels are the other networks using? Which channel are you using?

    Exactly what does this mean?

    Is the Mac hogging all the available bandwidth? Is it even doing network transfers at the time (Activity Monitor.app, Network tab)?

    When the Mac is connected, is it wired or wireless? What happens if you switch it (from wireless to wired, or vice versa)?

    What Mac model is it? OS version?

    Which of the other devices are wireless? Which are wired? What happens if you switch them?

    How? Activity Monitor? Something else?

    What's your max upload bandwidth?

    This could easily be the root of the problem, and would prevent other devices from making connections if an upload is consuming all outgoing bandwidth.

    The next step is to identify some possible candidates for what's causing this activity. To even attempt that, we need to know your OS X version.
  3. hallux, Jul 9, 2013
    Last edited: Jul 9, 2013

    hallux thread starter macrumors 68030


    Apr 25, 2012
    No all around, but until yesterday the drops were survivable (lasted only a couple minutes) and had been non-existant since the router swap

    Motorola SB6141

    Motorola SB6121

    Didn't seem to. Both routers had been used at some point or another.

    Haven't gotten that far, with the Linksys. The Netgear wasn't as much of a concern because it was on the 5 Ghz and the only 2.4 devices were my phone and personal tablet

    MAYBE 3 Mbps download, if I can connect at all, testing using speedtest.net. I pay for 15 and normally get close to 50%-70% better

    Last night the red line was consistently near the top of the graph, today it's spiking but MUCH lower (on a different network right now as I'm at work)

    Tried both, same results. Even plugged the Mac directly to the modem and had slow transfer speeds.

    The one in my sig. Mid-2012 15", running 10.8.4

    Only the desktop and printer are wired, all the rest (based on their descriptions) would be wireless.

    In the world of tech I made a BIG no-no. I should know better than this. I applied an update to my router around the same time as the modem swap. That update has caused other issues (iTunes home sharing won't work unless I reboot the router, file sharing from the Windows desktop, seeing the network printer) so I think the previous drops could be the router.
  4. chown33 macrumors 604

    Aug 9, 2009
    Thanks for the extra info.

    What's your max upload speed?

    When you say "the red line", you mean Activity Monitor, Network tab, right? Details are important.

    When it's at the top of the Activity Monitor graph, what's the MB/sec rate? On your home network, is that number consistent with your max upload bandwidth?

    If the outgoing network activity (red line in Activity Monitor > Network) is at its maximum, then incoming (download) network activity will suffer. This is because every packet received by a computer must be acknowledged (acked), otherwise the sender at the other endpoint will reduce the send rate. So if the Mac is consuming all the outgoing bandwidth available from your cable modem (note: the router is largely irrelevant), then all additional uploads and downloads will be slow. This is not Mac-specific; it's fundamentally how TCP/IP works.

    So let's assume the Mac is consuming all the outgoing bandwidth for some reason. The next step would be to find out which task or process is doing this. For this, the 'nettop' command in Terminal may be informative. You have to run it while the upload is occurring. Running it when no network activity is happening serves no useful purpose.

    You should practice using nettop when known network activity is occurring, such as when you're doing a big download in a browser. Learn how to use delta mode, and all its other features, so you can get the info you need the next time the unexpected upload happens. Capturing ephemeral activities requires being prepared.

    Another possibility is to get Little Snitch and have it ask you to confirm all outgoing network activity that happens. This will be like a breakpoint in debugging, where it will stop at the start of when something happens, so you can manually intervene or observe.

    Based on the information given so far, a not-entirely-wild guess is that CrashPlan might be doing a backup. It's also conceivable that something is performing a large sync between some on-Mac and remote files, if you have any sync services active.

    I can't think of too many things other than remote backups or remote sync services that would consume a lot of upload bandwidth. Download bandwidth can be consumed by many things that run by default on OS X, such as automatic software updates, help daemon, etc. But none of those things have any need for large uploads, so those seem unlikely.
  5. hallux thread starter macrumors 68030


    Apr 25, 2012
    Looks like it was CrashPlan. Only reason I didn't think it was before was because it didn't settle down when I killed the process last night. I paused the CrashPlan backup today when it started backing up and causing the same type of issue and I was almost instantly back in business. Very unusual since I saw no issues like that when I did the initial backup.

    Yes, I meant the red line on activity monitor on the network tab. I don't recall what the bandwidth usage was.

    I pay for 15/1 but normally get close to 26 down based on speedtest.net.
  6. chown33 macrumors 604

    Aug 9, 2009
    I'm glad you worked out what it was.

    I friend of mine suggested this:

    I have not tried it yet.

    Maybe one of its settings is broken. I'm unfamiliar with CrashPlan's specific features, but some sync/backup programs allow you to set a bandwidth ceiling that the app will enforce on itself. If that ceiling somehow got changed, CrashPlan could be running amuck.
  7. hallux thread starter macrumors 68030


    Apr 25, 2012
    It does, I never configured the cap settings before. I've set it to 200 kbps to hopefully prevent this form happening again.


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