Performance in a mostly switched Environment

[gary_the_network_guy]

So I was wondering how to address performance issues in a mostly switched environment?

Are there any ideas or steps some of you could suggest.

My only idea is to track down the taken links from a access-switch to the core router and looking at the statistics of 

show interface.

Are there better ways to debug performance issues, I also know Iperf. but the only thing you can do with that is sending tcp or udp segments over your lan.

[balaji.bandi]

First we need to understand what kind of performance issue ? network or application ?

is this performance issue only certain time or all time ? what is the utilisation on the uplinks ?

in general my check list in the network level  - capture information and see any obnormal, also check any bugs around that version of code.

show processes cpu
show processes cpu history
show processes cpu sorted
show controllers cpu-interface
show controller ethernet-controller
show platform tcam
show platform ip unicast
show interfaces counters
show spanning-tree - issue
show ip traffic

[marce1000]

 - For large sites , which lots of network equipment and core(s) , you may look into Cisco Prime, which offers that in a Dashboard , including flexible alerting , etc.

 M.

[gary_the_network_guy]

Yeah, but a lot of Users complain about slow running Applications, how do I troubleshoot those in a mostly switched environment?

The Cisco Prime is great and all but it only shows int utilization

[Georg Pauwen]

Hello,

I think your original approach (sh interfaces) is a very good start. Have a look at the output of the interfaces from the host to the switch where the application is hosted, and check for things like input/output drops.

Do you have any QoS (quality of service) configured in your network ?

[gary_the_network_guy]

No as far as I know there is no QoS. If I am being honest I wouldn't know how to implement QoS or even find out what Apps need certain requirements

[balaji.bandi]

Users complain about slow running Applications  - this is biggest task, until you ask the questions as suggested :

First we need to understand what kind of performance issue ?

application ?  what application ? where is this application trying to connect ? inside Lan or outside Lan (Internet) ?

is this performance issue only certain time or all time ? what is the utilisation on the uplinks ?

[Marvin Rhoads]

Using most modern enterprise class switches, most performance issues are due to overall design vs individual switch performance. Once you've checked for common issues such as speed and duplex mismatches (or wireless performance issues such as oversubscribed APs and crowded RF spectrum) then look into inter-switch link utilization. Most any NMS can help you track and visualize that data (Cisco Prime Infrastructure, SolarWinds NPM, PRTG, etc.).

[Joseph W. Doherty · Accepted solution]

For a switched, wired network, 99 times out of hundred, it's not "true" network performance problem, other than possibly over-subscription, but you do need to remember that 1 time in a hundred it is.

Two common problems are whenever there's distance based latency involved, just a few extra millisecond here and there can slow performance much more than expected or developer/test setups often are much, much better than production setups and applications perform much slower on the latter than the former or have problems of "scale" when running in a production environment.  (The reason understanding the latter is important, when there are performance issues for network based applications, often someone will say how well the application works in a developer or test environment, so when used in production, poor performance must be because of the network.)

Anyway, first insure all the interfaces, end-to-end, are not showing any kinds of errors, and very few drops.  Don't get overly concerned about utilization, alone, whether it seems good or bad.  (Utilization, I believe, is often very much misunderstood.)

If WiFi is involved (hopefully not for you), its performance depends so many things not being "bad", but in an ideal environment, it can perform about as well as a wired switch having a single half duplex host, per port, at whatever best bandwidth the AP and host share (often less than what a wired connection can support).