Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Network Card speeds (100 full or Auto)

We are doing a test on our network right now to see if 100 full or Auto is a faster setting, and from what I can tell our Cisco switches like the auto setting better than 100 full(nic and switch port).

We put 2 pc's on the same switch, same vlan, put them both at 100 full and tried to transfer a 500mg file and it seemed to lag really bad??? I do not really understand why this is. I transferred an 800mg file from a server and it transferred in 3 min (Auto).

The whole point for this test is our developers are saying the network is causing their application to run slow????


Re: Network Card speeds (100 full or Auto)

Did you reboot the pc when you changed the nic setting. If it still thought it was auto then it would default to half duplex when you change the switch to a hardcoded speed/duplex and you would have a speed/duplex mismatch which would cause really slow performance and errors on the link .

Cisco Employee

Re: Network Card speeds (100 full or Auto)

Once a NIC has established link with a switchport (whether by negotiation or manual coding), it has no bearing on traffic forwarding. Now, if you're hard coding the NIC to 100/full and leaving the switchport at auto, that's an invalid configuration, and you will very likely see a performance impact.

That scenario aside, the switches have minimal buffering and will either forward or drop a packet upon receipt. So unless you are seeing drops along the path of the transfer, the network as a cause of slow applications is likely a red herring.



*Please rate helpful posts.

New Member

Re: Network Card speeds (100 full or Auto)

Thanks for both of your replies. I just got off the phone with cisco and they are saying "Auto" is always the best way to go..... Can anyone comment on this? We also run some commands on my 3560/3550 and our core 3750 and they both show cpu utilization @ 1-4% the core being the 4%. Is this bad/good? Also is there any other commands I can run to see how my network is performaning?

Any suggestions on how to approach these developers with this information? Should I tell them " it's your shit fix it?" lol jk

Any info would be great.


Re: Network Card speeds (100 full or Auto)

Unless you are seeing errors somewhere along the path then it likely a app issue . Just make sure the pc nic and switchport settings match exactly.