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Just got a new 50 megabit pipe into the company. When connecting a laptop directly to the connection, I can get 50 megabits by doing a bandwidth test.

Under normal conditions, our connection is plugged into our Windows Server. Our windows server is the domain controller and DHCP and is connected to a switch.

When connecting through the switch, I can only get 10 megabits. What is the best way to find out what is limiting the connection.

This is what I know so far:

  1. The windows server that is connected directly only gets 10 megabits. However, all wiring is 5e and both network cards are at least 10/100.
  2. There are two switches. One connected into the other. They both are at least 10/100.
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Your domain controller is your firewall? Really? You should consider buying a dedicated device for this. – pauska Oct 7 '10 at 14:47
see screenshot... looks like both NICs on the server are running at 100Mbps One is for the connection coming in.. the other is for the connection going out. – majestiq Oct 7 '10 at 14:53
Fair enough, but what are the switch ports running at? The server ports are only half of the equation here. – EEAA Oct 7 '10 at 14:55
Also - you haven't patched this server in 866 days and you're using it as your firewall/router? That's incredibly foolish. You're just asking for problems. Get that thing patched! – EEAA Oct 7 '10 at 14:56
up vote 5 down vote accepted

A couple ideas:

  1. Duplex mismatch. I assume you have the server and switch ports set to autonegotiate. Make sure that the autoneg is working correctly and that they're agreeing on 100/full duplex. If they're not agreeing properly, then one is likely falling back to 10/half duplex. It's normally best practice to just leave all ports set to autonegotiate, but if that's not working, you may need to force them to 100/full.

  2. Crappy switch. What kind of a switch is it? It's possible that it's a cheap consumer-grade switch and that its backplane is really only capable of passing 10Mbit.

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Are the switches managed? I would check to see if the switch was set to autonegotiate the connection to 10mbps.

Also, I would try different cables. Often switches and NIC's are intelligent enough to gracefully degrade to a lower speed if they detect noise or other limiting factors on the network.

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That topology is odd - usually you'd run the router into the switch then the clients and servers would come from the same switch/es - you must be using connection sharing, which is a bit 'ghetto' when using a proper server - ok for home but likely to have performance issues when done professionally.

Now onto the problem, have you checked that the server NIC is working at 100Mbps? Tfull-duplex? The problem is clearly related to the server if it's only getting 10Mbps itself.

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how can I check this? – majestiq Oct 7 '10 at 14:47
look in control panel, networks - then under each NICs settings - if you can't do this then maybe you shouldn't be doing this job to be honest – Chopper3 Oct 7 '10 at 15:05

Have you clocked the throughput performance at the server, just in case it is the server's packet switching that is causing the slowdown?

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