I have been asked to look into the performance of my LAN as it seems "slow". I have started some initial testing with iperf from my desktop to servers and from servers to servers. I think I understand the output, but I just wanted to make sure I do with someone has used it before. for instance when i run a test between my desktop and a server i get something like the following:
I'm not too sure how netperf works, but there are a few things I see that can make this value lower than expected:
Depending on how iperf makes the calculation, it may not take into account ethernet or IP overhead. If it is calculating how long it takes to send the raw data across, you need to factor in a 14-byte ethernet header and 20-byte IP header. If it is sending 1500-byte packets (best case), the overhead is at about 2%. This would put your actual throughput at 830Mbps.
2. Server speed
Every packet you're sending to this server needs to be processed and acknowledged in order to count. Chances are your server cant keep up with a gig worth of traffic, and instead is only processing about 813Mbps.
3. Switch/router oversubscription
There are shared points on every part of a network, such as interface buffers on routers/switches, backplane bandwidth, uplink ports, etc. If any of these is congested, you wont get a full 1Gb through.
813Mbps is better than most people would expect out of a gigabit switched network, and it certainly disputes any claims of a 'slow network'.
Thank you very much for your reply. One thing I have noticed is that if I do the same test the other way, from server to workstation...I get about half of what I do in the first test. roughly 500Mbps. Is there some reason it would be slower one way and not the other? Would any of that have to do with how fast my pc can process info coming from the server?
I highly recommend you not test/troubleshoot reports of "slow network" with iperf. You are just creating traffic that could cause more problems...
That being said, this issue plagues all of us in the networking industry and the first step is to ask WHAT is slow and why the user thinks that. It could be their application... It could be a database.... It could be hundreds of things, none of which are related to the LAN.
I suggest you ask why they think it's slow. Go through your switches and look for logs that look out of the ordinary. Check the actual port the users plug into and watch out for 100/half-duplex... I've seen that one 1000's of times. Check your STP architecture and make sure STP isn't flapping.
Blasting packets will not find the issue... That is reserved for special troubleshooting cases that are not required here...
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.