LAN Bandwidth Question

Posted on 2011-02-14
Medium Priority
Last Modified: 2012-05-11
I have a stupid question, but I need some help understanding.

I have a gig switch and gig cards in all of the my computers and severs.  The office is wired to CAT5e.  When I run a LAN speed test I only get 421MBPS write and 398MBPS Read.  Should I be getting 1,000 MBPS since everything is a gig or are the speeds that I am getting acceptable?
Question by:commeng

Accepted Solution

ZombieAutopsy earned 400 total points
ID: 34888592
How are the NIC's configured, are they set to automatic speed and duplex, same on the switches where are there settings. make sure everything is set to auto.

Assisted Solution

foochar earned 400 total points
ID: 34888644
Those speeds are comparable to what I see in my LAN environment on gigabit equipment.  Keep in mind that the rated speed assumes that the rest of the hardware in the source and destination can keep up with network card.  It also depends on the latency in your network, as well as the size of the tcp windows.  I've done some cursory checks into enabling jumbo frames on the network but haven't worked through all the details as of yet...

Assisted Solution

mikegatti earned 400 total points
ID: 34889244
Jumbos frames will definitely help as it allows more data to be transmitted across the network with less processing by switches and servers (more data moved with less source/destination look-ups of mac addresses), There is also some additional work that you can do in terms of tuning the TCP stack of your endpoints by increasing window sizes and buffers, but this can come at a cost of WAN performance.

The type of application also has a great affect in the tests that you are doing as well as the protocol you are using (chatty applications such as SMB are bad for testing). If you want to test if you network is capable of handling transmitting data you should try to use UDP as there is no need for the destination to ack the the receipt of the packets.
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LVL 24

Assisted Solution

rfc1180 earned 400 total points
ID: 34893517
Be careful in utilizing jumbo frames in your network, be careful for what you ask for. Smaller frames are less effiecient in a network, so in a 1 Gigabit network that is using 1538 bytes frames (Assuming untagged frames) will get you between 405Mbps (theoretical).

LVL 17

Assisted Solution

surbabu140977 earned 400 total points
ID: 34895751
To answer a one liner, you won't get gig speed if your cabling is gig. Why, how is a different topic altogether. What you are getting is very much acceptable since my own laptop received 100meg in my office gig network.


Author Closing Comment

ID: 34895939
Thank you, that is what I thought but I needed confirmation.

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