[K12OSN] Testing actual network speeds

["Terrell Prudé Jr."]

Dan Young wrote:
> Carl Keil wrote:
>   
>> Can anyone suggest a way to test my LAN speeds that I'm using for
>> K12LTSP?  Screen redraws are jerky and slow on some of my clients.  I've
>> always suspected my network cabling wasn't quite right, but I don't know
>> how to test it.
>>     
>
> You can check for errors and find out what speed your NICs are
> negotiating with ifconfig and ethtool. Substitute your ethernet
> interfaces for eth0 (i.e. it may be eth1, etc.)
>
> "ifconfig eth0 | grep errors"
> Any number of errors is not good, especially if that number rises much
> over time.
>
> "ethtool eth0"
> Look at speed and duplex.
>
> Throughput can be monitored with iptraf (install w/ yum). The detailed
> interface statistics can tell you incoming/outgoing kbps.
>
> If your switches are "managed", you might want to use their command-line
> or web interfaces to look for CRC errors or similar. With these kind of
> problems, it pays to be methodical and check every device/port between
> the server and the client.
>
>   

And to actually generate some test traffic, I take a reasonably powerful
box (dual-Athlon desktop, Core Duo laptop, or whatever) and use the
following command:

[microman at takhisis ~]$ su root
Password:
[root at takhisis microman]# ping -f -s 15000 w.x.y.z

where w.x.y.z is some other pretty beefy box on the other side of the
link.  What you're doing here is called a "flood" ping, and you're
specifying a packet size of 15,000 bytes/packet.  I will do this until I
fill up the link.  I've actually pegged an OC-12c with multiple such
ping sessions.  I would have, say, four of these from Box A pinging Box
B, and I'd have another four or so from Box B going to Box A.  So, you
should have no trouble filling up a 100Mbps client link.

Here's another way:  fire up full-screen TuxType or TuxMath sessions on
all of your clients, simultaneously.  This *WILL* generate a boatload of
traffic.  All you need are 15 simultaneous sessions of this to peg the
server's Gig-E link (one of them will use 73Mb/sec).

Then, as Dan mentions above, check out the port statistics on your
switch, assuming that it's a managed switch (e. g. BayStack 450T, Cisco
Catalyst, or Amer.com SR48G2i).  If you're not using a managed switch,
it actually would be a wise investment; 24-port BayStack 450T's with a
fiber Gig-E interface can be had on eBay for about $200.  They work
really well.

--TP
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