Raspberry Pi slows down internet access for the whole network

Question

Whenever my Raspberry Pi is connected to the network (via ethernet) the entire network is slowed to a crawl. On my main computer, ping times for google.com go from ~10ms to ~200ms and it takes forever to load web pages. Connections are also slow on the Pi, with an apt-get update showing pathetic speeds in the order of 1KB/s. Turning off the Pi completely removes the drag from the network. Interestingly, the local network appears to be fine, with scp copying files at reasonable rates; around 4.5MB/s to the Pi.

I've tried static and dynamic IP addresses for the Pi, but both have the same problems. Switching from Raspbian to Arch also had no effect.

I've checked the connection's duplex with dmesg | grep -i duplex, which shows that the Pi's connection is running at 100Mbps, full-duplex, as expected.

My modem/router is a Billion 7404VNPX (an Australian thing); relatively high-end, albeit a bit buggy at times (it will occasionally delete all its firewall settings). It assigns IPs in the range 192.168.1.1 to 192.168.1.20 and has 192.168.1.254 as its own IP. When I assign static IPs I tend to use the 192.168.1.200 area. I recently tested the connection with the Pi plugged straight into the modem (rather than via a wall socket) and it managed to crash it entirely!

I am starting to suspect that my modem isn't as reliable as I previously thought, so I'll try and get onto someone else's wired network in the next few days.

Solution

You talk about it slowing the entire network and then just reference a ping to Google. There is a big difference between LAN and WAN. Assuming you are just having slowness over your WAN to external sites, have you ruled out that the Pi is downloading anything? It tends to download updates/install packages on a fresh install of many applications.

Comments

[Ramhound]

It sounds like the network device on the Raspberry Pi is to blame. Are you connecting to your connection through the Wireless or Lan adapter?

[michaelsproul]

@david My thinking exactly, it must be doing something to the WAN, although I can't work out what, and it seems to be OS independent. I'm using the ethernet port on the pi at the moment, but I have a USB wifi adapter that I'll try out... (I suspect this will fix it, although it's less than ideal)

[michaelsproul]

Interesting, I just tried a file transfer from my desktop to the Pi and it averaged around 4.5MB/s, which isn't too shabby considering the 100mbit connection and the slow SD card. However I don't think the Pi is up to anything; netstat just shows the ssh connection and some ntp time stuff. I disabled ntp in case it was pestering the time server or something silly, but it made no difference.

[michaelsproul]

Do you reckon 4.5MB/s is too slow for writing to an SD card? I thought that seemed kind of ok

[JohnnyVegas]

What class is the SD card? I always use class 10

[michaelsproul]

I just tried it with a crossover cable and got 4.5MB/s again. The card is class 4 though, and dd'ing zeros runs at about 7MB/s

[JohnnyVegas]

The class is more or less equal to MB per sec. 1 for 1mb/s etc. sounds about right for a C4. A C10 is about 9.5mb/s for me.

[Dmitry Grigoryev]

If you think that the answer is not satisfactory, what is your motivation to post it?

[Andrew]

My motivation was to highlight that (a) the problem still exists, (b) earlier discussions seemed to be side-tracked onto LAN questions, (c) my testing suggests that the router is somehow being upset such that the WAN connection suffers.

[Andrew]

Enquiries elsewhere have elicited suggestions to look at problems with signal-to-noise ratio on the WAN connection caused by common mode noise induced by the Pi's PSU, or memory leaks in the router induced by some strange DHCP or dynamic DNS behaviour.