Slow LAN

Posted on 2007-03-24
Last Modified: 2008-05-15
Our lan is running extremely slow and its my job to make it faster. The infrastructure consists of 1 router for internet access and vpn's. 1 10mbps switch, 1 100mbps switch, 5 dedicated servers for mail, ad, accounts, files, 30 desktops.
All servers have gigabit nic's, all desktops have 100mbps nic's, all cabling is cat5.
Im getting approx 2mbps transfer rate between desktops and servers on the lan which is not good considering all users and desktops are part of a domain.
Would the 10mbps switch be slowing the lan down to this speed on its own, or could there be another possible bottleneck?

Sorry if ive left anything out.
Question by:aaronmcl
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LVL 69

Accepted Solution

Qlemo earned 150 total points
ID: 18785912
Whethter the 10mbps switch effects speed depends on the 100mbps switch. Has it one backplane for every speed (cheap old products did often), then traffic destinated to the slow switch reduces overall performance. Simple test would be to plug it out, and see what happens to your transfer rates.

Have a look at the collision rate, e.g. on one client with netstat -s. Collisions should be seldom compared to number of transferred packets.

Another cause might be mixed half and full duplex. Try to fix the NICs settings to e.g. 100mbps/full duplex, and do so on the switch (important!). Test again, if that helps.
LVL 29

Expert Comment

by:Alan Huseyin Kayahan
ID: 18785927
       "All cabling cat5e" > You must use at least CAT5E cabling for gigabits (servers) run properly.
        *You should throw the 10mbps swithc to wastebasket immediately.
        *If possible, buy a swithc which has some gigabit ports for your servers.
        *Make sure the disks are defragmented. Fragmentation will also decrease the transfer.
        *If possible, remake your network with cat5e.

Author Comment

ID: 18785979
I have a 10/100mbps switch with a few gigabit ports ordered already. Should have it early next week.
I will try defraging the servers tomorrow see if that helps.
Its not possible at this moment to re-wire the building with cat5e.
What speed should i expect with this setup?

Could the 10base switch cause this bottleneck on its own?
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LVL 69

Expert Comment

ID: 18786210
The bets go 80:20 against your 10B-Switch ...
LVL 40

Assisted Solution

Fatal_Exception earned 100 total points
ID: 18786456
With CAT5 only, you cannot expect much of a performance boost when moving from 100 Mbps to 1000 Mbps..  it just was not made to the stringent standards that 1 Gbps speeds require...   You are probably spinning your wheels and wasting money moving to a 1 Gbps ports on your switch / router...  You might want to make sure you are operating at Duplex, and all your NICs are setup in the same way..    to test collisions, you could place a sniffer on the network and see what the packets are doing..  Ethereal is good, and MS has a new Network Monitor that can be downloaded..

Author Comment

ID: 18787797
I have to upgrade this switch anyway, so i figured i may as well allow for future upgrades by putting the servers on their own gigabit port.  
My point is im only getting around 2mbps at the minute, so i should notice a considerable increase in speed after upgrading the switch and ensuring all network devices are operating at 100/full duplex.
Ive had a play about with ethereal but need to figure out how to use it properly before i bother doing any sniffing.
Ill post back tomorrow after ive carried out my testing and award points then.
LVL 40

Expert Comment

ID: 18788027
After thinking more about this, I fired up Ethereal and realized that it does not actually find collisions on a network..  So I did a search for this, and found this link, and decided I had better post it:

If your switch is located in the server rack, you might be able to increase your bandwidth by connecting the servers directly via 1Gbps ports to and from the servers..  but you will need at the minimum Cat5e, and preferably Cat6 patch cables between them..  This is most likely where any bottlenecks happen anyway...
LVL 30

Expert Comment

ID: 18790131
>My point is im only getting around 2mbps at the minute, so i should notice a considerable increase in speed

What tool did you use to arrive at that figure?

Don't even bother with Etheral for speed testing,it isn't what you want to test raw bandwidth.

Use Iperf

Try this:

Set up one WS as server  iperf  -s

The other as client

iperf  -c  XXX.XXX.XXX.XXX.XXX

xxx= ip address of iperf server

This will give you raw throughput and test the infrastructure.

Ethereal is more of a tool to look for routing issues and poorly written programs.
LVL 30

Expert Comment

ID: 18790139
Where is the 10 mb hub located?
To the servers,desktops router?
LVL 40

Expert Comment

ID: 18799074
Thanks, and best of luck with this..


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