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10/100 ethernet network speed question.

Posted on 2010-09-16
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Last Modified: 2012-05-10
I am sure this is a rather easy question for some of you Cisco guys/ gals, but I have tried troubleshooting a speed issue within my small office.

Basically, I have a comcast business class router that is connected to a netgear 10/100 24 port unmanaged switch (unmanaged -  I can't make any changes, VLANs, etc) that then has only 8 ports being utilized by ethernet CAT 6.  There are five systems that are connected all the time and each has a 10/100 or GB NIC.  I set the NICs to full duplex 100.

With that being configured the way it is you would assume that file transfer rates between computers would be above the 10 MB and less than 100 MB rate.  However, whenever I start transfering large files < 1GB, I will consistantly get connection speeds in the 1 - 3 MB range.  I have sniffed the network and really don't see much traffic that would slow down the connection.

I was guessing that it was the router that was the cause behind this since it controls the DHCP, etc.  Is that correct?  Should I put another router behind the modem/ comcast router that can switch at the 10/100 MB level for internal files?

Your expertise is much appreciated.
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Question by:shark1998
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by:Dave Baldwin
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What transfer method and from where to where?
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by:shark1998
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Simple TCP/ IP.  The longest cable length is less than 100 FT.
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by:kf4zmt
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I think what DaveBaldwin is asking is are you using ftp, windows file copy, etc to move the files?  Also, are the files being transferred between two computers on your local network or is one computer on the other side of a slow connection such as a WAN or the Internet?  I assume across your LAN since you mention a 100 ft cable.
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by:giltjr
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There is no such transfer method called "simple TCP/IP."

TCP/IP are two protocols that are used by other higher level protocols (CIFS/Samba/SMB or ftp).

My guess is you are using files shares/drive mapping which would use CIFS/Samba.

When you are doing the transfers what are you using to measure the through put.

Network speeds are normally measured in bits per second (represented by a little b), 10 Mbps = 10 million bits per second and 100 Mbps is 100 million bits per second.  


Some software that shows/measures through-put will use Bytes per second (represented by a big B).  A 10 million bit per second (Mbps) connection can transfer data at a max of 1.2 million bytes per second (MBps).  A 100 Mbps connection can do 12 MBps.

Using typicall CIFS/Samba a 100 Mbps connection will get anywhere between 3 and 10 MBps.

Typically I would leave the NIC configured for auto speed and auto duplex.
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woodmouse earned 167 total points
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I would try to check, if nothing else is the culprit here.
Download iperf on both server and client, and see if you get a reasonable value...

"iperf /s" on the server
"iperf /c <ip-server>" on the client

You should get values around 96 ~ 97 mbit/sec !
If you drop below 90 mbit/sec - then you either have a fault or bad ethernet-cable - or a bad switch...

I've rescued many network-dips/hogs using this technique...
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by:Dave Baldwin
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Yes, FTP, Windows Explorer (SMB), Web Form/HTTP?  All of these have different overhead that limits the speed you will see.  Also, how many switches/computers/routers does the path go thru?  Do any of them filter content?
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by:Rich Weissler
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A 100 Mbps (mega-bits per second), has a theoretical maximum transfer rate of 12.5 MBps (mega-bytes per second), (8 bits per byte) if it could run flat out.... no overhead, no contention on the bus, etc.

The overhead is probably relatively low... I could track down real numbers if you need it... but assume you lose at least 5% for overhead (packet headers, frame headers, etc  worse for small packets... not as back for huge transfers.)

As the pipe gets more crowded, contention gets worse though... I used to hear that a pipe 30% full was pretty good... go much above that, there was going to be more contention... but that was back in the days before switches were popular.  However, if everyone is trying to talk to ONE machine, that might still be valid.

1-3 MBps doesn't sound too bad... I wouldn't expect you to get much more than double that... maybe 8 MBps in an absolute ideal situation.

As a side note:  I know in environments in which I've lived before... if the workstation NIC is locked to 100 FULL, and the switch port is auto-negotiating, sometimes 'bad things' happen... if netgear indicates their gear doesn't have a problem, you're probably kosher, but it might be worth double checking.
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by:Rich Weissler
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Eep!  Sorry... that's what I get for allowing folks to talk to me while answering questions.  :-)  Ignore my response... my points were already made.
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by:shark1998
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Thanks all.  I will try some more troubleshooting and get back to you and divy out points.  There is a lot of good information here.
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by:kf4zmt
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@woodmouse

Where can I get a copy of iperf for Windows?
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by:woodmouse
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google "iperf windows download"... (without the quotes).
I just did this for you : http://www.noc.ucf.edu/Tools/Iperf/

You don't have to install it, it's a dos-based util - copy it on both locations to a temp folder. good luck!
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by:kuoh
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Since you have an unmanaged switch, I would recommend setting the NICs to autodetect on all the PCs to avoid duplex mismatches.  While this may not solve all your speed issues, it should at least take away one potential cause.

http://happyrouter.com/cisco-ios-duplex-mismatch-primer
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