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Unknown app using the Internet

D

drewc1138

macrumors 6502
Original poster
I'm having an issue with something on my iMac using up my bandwidth on my home network.*

Over the past few days I've noticed that my Internet has been CRAWLING. I did a speedtest.net test, and the download was about normal, but the upload speed was anywhere between 3 kbps and 15 kbps, instead of my usual 300 kbps (not stellar, I know, but it's the best I can get). When I look at my wireless router, the indicator light for Ethernet is constantly flashing, showing that there is some activity, even though nothing is happening. I will even go in and close out every app, do a complete restart even, and something continues to use it up. When I shut down my iMac, the upload speed jumps back up to normal on my MacBook and iPhone, but when it's restarted, it slows to pre-dialup speeds again, so I know that it's something on the iMac.*

I just don't know how to find it. I've tried poking around in the Activity Monitor, but I don't find anything too out of place. I'm sure there's a simple fix, I just don't know what it is. Any suggestions would be appreciated.*
 
What kind of connection do you have (Cable, DSL, satellite)? Is the modem showing the same activity?
 
The basic answer is that cable is a shared connection, and as such, you should pretty much always see a bunch of traffic across it. It may not be destined for you, but you're seeing all the other stuff in your neighborhood. Also, as a shared connection, the total bandwidth advertised is a maximum a user may see with minimal other traffic; if everybody in the neighborhood is streaming or downloading a lot, it'll toast your bandwidth.

To see this in action, try turning off all of your internet-connected devices, you'll still see the modem going like gangbusters, especially in the evenings.
 
JNB said:
To see this in action, try turning off all of your internet-connected devices, you'll still see the modem going like gangbusters, especially in the evenings.
Click to expand...

That's just the thing...if I take my iMac off of the network, everything else runs smoothly.

I have my iMac plugged directly into my linksys router through ethernet. When it's plugged in, everything crawls.

If I unplug the iMac, everything that connects wirelessly starts working perfectly. If I connect the iMac to the network over WiFi, everything starts crawling again. If I unplug the ethernet from the router and plug it directly from my modem into the iMac, it crawls. If I do the same and plug directly into my MacBook, it flies. Anytime the iMac is NOT on the network, the PC/Activity indicator on my modem is solid. Anytime the iMac IS connected, it's going, as you said, like gangbusters.

I get what you're saying about bottlenecking and all that, but it just seems like every piece of evidence points to this being an issue with my iMac.
 
I have something to try which may help work out if it is the imac or a setting in the router.

Open System Preferences/Network with the connection to the imac show the dhcp with the ip number and router info. Click renew release.

This causes the connection to get a new lease from the router.

Lets know if that makes any even a small difference.

If that doesn't work try this

open the terminal and type or copy and paste the following

sudo dscacheutil -flushcache

you will need to enter your admin password for it to work.

Lets know what happens and I will help further as I have used Linksys router in the past and seen a few strange issues with slow connection.
 
Have you looked at Activity Monitor to see what processes are running that may be the cause? Also, take a look at the Login Items for your user for anything that you may have installed that could be constantly generating network activity. Lastly, consider (temporarily) creating a new Standard User account, start up logging into that and see if the problem persists.
 
A Terminal Command to try

lsof | grep IPv4

This will list all applications that have an open internet connection. My advice close down everything you expect to use the internet on the iMac, plug it into a wired network connection, then use this command.
 
Get a Program called 'Little Snitch' on your offending machine.

The program will query every outbound internet connection (from that particular mac). If something is trying to talk - Little Snitch will make you aware of it.

http://www.obdev.at/products/littlesnitch/index.html

You get a 3 hour free trial, afterwards you should pay 30 euros to get the proper serial / license.
 
Tried everything that you said, Robert, and something worked, because it's doing much better now. Thanks, guys!
 
dav146 said:
Get a Program called 'Little Snitch' on your offending machine.

The program will query every outbound internet connection (from that particular mac). If something is trying to talk - Little Snitch will make you aware of it.

http://www.obdev.at/products/littlesnitch/index.html

You get a 3 hour free trial, afterwards you should pay 30 euros to get the proper serial / license.
Click to expand...

I have to second this. greatest little tool.
 
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