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Need help with a ridiculous statement

Hey all,

A little background info:

Our client PC's are connected to a Cisco Catalyst 2950 Switch with a port speed of 10MBPS/Half Duplex. We also have a server connected to this same switch, but the switch port speed for this server is set to 100Mbps/Full Duplex. The client NIC's are set to autonegotiate. Cabling is Cat5e.

I would like to have the port speed for the client PC's changed to 100MBPS/Full Duplex. I was told the following when I requested the change to 100/Full:

"The reason that we would not want 100MB for PCs is that if there were a rogue NIC card in a PC on a 100MB port it would cause far more problems to the network."

As I don't have a networking background, I need some help in refuting this statement. Can someone point me to some whitepapers that will disprove this statement and/or offer some advice?


  • Other Network Infrastructure Subjects

Re: Need help with a ridiculous statement

Here is the low down. They could be right. Let's say you set your switch to 100/full and all your PC's to 100/full, this is a good configuration. Now based on that, someone changes the NIC settings or as was put to you...a rouge NIC that was set to Auto was introduced to your network, you would have network problem because you would have Duplex mismatch. Now if you set both the switch and the PC's NIC's to Auto, again a good configuration, you again could have a problem if a NIC was introduced that was set to 100/ would be Duplex mismatch. I could go on with the different combonations. Here are two Cisco papers to look at.... one is called Troubleshooting Cisco Catalyst Switches to NIC Compatibility Issues.... and the other is..... Configuring and Troubleshooting Ethernet 10/100/1000Mb half/Full duplex Auto-Negotion

Hope this helps,



Re: Need help with a ridiculous statement

Duplex/speed/auto-negotiation mismatches will indeed cause issues (CRC, input errors, etc) but only from the PC to the switch. These errors won't propigate to other parts of the network.

I don't think they are talking about those kind of issues. What they are probably talking about is if a PC has a NIC that is only operating at 10MB/half duplex and it decides to send a bunch of packets to other devices on your network for whatever reason (bad NIC, computer virus/worm, etc) it can only send frames at 10MB. If you have the port set to 100MB full duplex, it can send the bad frames at least 10x faster (20x if full duplex is being fully used) they are kinda correct.

If the PCs aren't experiencing any slowdowns due to not having enough bandwidth, it may be wise not to even aruge the point with them. If the PCs are experiencing slowdowns are something, then it may be worth discussing the issue.

My personal opinion is if a rogue NIC/virus is sending data out to a switch port, it doesn't matter too much if it's going at 10Mbps or 100Mbps, the damage will still occur.

My $.02


Re: Need help with a ridiculous statement

The usual argument here is not a rogue NIC problem but potential overloading of the server. Most new PC's are capable of driving a 100MB/Full-Duplex NIC to almost full capacity; the Server can only match this and not exceed it. Potentially multiple users running 100Mb/Full-Duplex would overload the Server as it just couldn't keep up. Running the Client NICs at 10/Half reduces this potential situation and forces the Client PC's to 'back-off' - sort of hides the problem.

If you are an Enterprise this is a bit of a 'smoke & mirrors' tactic from your Network support guys as they should be catering for higher bandwidth access to servers - this is 2003.....

If you are not an Enterprise and you are in fact a small company with 1 switch then this is probably a reasonable approach, although I would query the expected performance of the Server in question.


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