How can Fedora determine the maximum speed of network computer cards?

[Rick Stevens]

On 11/13/2015 01:44 PM, Paul Smith wrote:
> On Fri, Nov 13, 2015 at 6:06 PM, Rick Stevens <ricks at alldigital.com> wrote:
>>>>
>>>> Is there something in Fedora that I might use to determine the
>>>> maximum
>>>> speed the network card of my computer can attain on Internet? I am
>>>> thinking about wired Internet and not about wireless Internet.
>>>>
>>>> Thanks in advance,
>>>
>>>
>>> You might need to explain the reason for your request since, it may
>>> change the answer.
>>>
>>> As an example, my computer has a GigE port that runs to a 100Mbit
>>> simple switch before getting to anything else.  So I would be limited
>>> to a theoretical maximum of 100Mbit but I might want to know how fast I
>>> can transfer files to/from another computer in my LAN.  The bottleneck
>>> here could be the switch, my NIC, the other computers NIC, OS limits,
>>> firewall slowdowns etc.
>>>
>>> So, for me I would really want to test an actual file transfer using a
>>> number of setups.  Depending on each computer I could try Samba, FTP,
>>> SCP.  I might run a wire to bypass the switch.  I might try with
>>> firewalls and antivirus disabled.
>>>
>>> All this will also give me some clue on how fast I could run if I was
>>> able to get a fiber connection, to let me know if my system would be a
>>> serious limit to getting the full 1G of true fiber.  Obviously the
>>> switch would have to be upgraded in my case.
>>
>>
>> Generally speaking, any given NIC that has proper firmware and is in
>> a relatively modern computer will run very close to the rated wire
>> speed--provided the other end of the cable can handle it as well. Note
>> that the effective transfer rate will usually be about 80-95% of that
>> (for a 1Gbps NIC, 800-950Mbps).
>>
>> This does not include any overhead involved in the protocol used. You
>> will find that things like FTP, rsync and the like will show lower
>> data transmission rates (e.g. multiplying the number of bytes
>> transferred by 8 to get number of bits transferred) due to their
>> overhead and that they're dealing with TCP's inherent nagle algorithm
>> and handshaking. TCP is designed to make sure things get to where
>> they're supposed to go, and with that comes a lot of overhead. Things
>> like UDR (rsync-over-UDP) will show much closer to the theoretical data
>> transmission rate due to its use of UDP.
>>
>> The most common bottleneck to raw speed is the wire, switch, router,
>> gateway or ISP that the NIC is connected to. You'll rarely find the NIC
>> itself the limiting factor.
>
> Thanks to all respondents! I could now determine that my network card
> is a 100Mbps Fast Ethernet, and now it is clear why the speed test
> (http://www.speedtest.net/) shows a download speed of just 85 Mbps
> when my contracted speed is 120 Mbps.

85Mbps sounds about right for a 100baseT NIC on one of those tests
(they typically use TCP). You can always verify your type of NIC using
ethtool.

My laptop has a 100baseT port. When I need gigabit, I use a USB3 gigabit
dongle. Note that you need USB3 for this--USB1.1 and USB2 aren't fast
enough.
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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
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