Wednesday, 3 June 2009

Router performance

Router performance can be affected by a number of things as there are several different aspects involved.

Resource issues, such as the performance of the CPU and RAM
Router IOS configuration changes
Bandwidth management: Quality of Service (QoS)
Layer 1 network issues: Bad circuits or cables
Errors and failure of the router hardware


Bandwidth management: Quality of Service (QoS)

To resolve performance issues or improve performance, you may need to implement some form of bandwidth and/or traffic management. This is commonly called (QoS) Quality of Service but there are many different types of QoS, and picking the right one for you depends on what your doing but one thing is for sure you should try to reduce traffic to only permitted types, as you don't want high utilization of interfaces.

One quick way to see what the utilization is on your LAN or WAN circuit is to use the show interfaces command and look for the TX/RX Load as well as the five-minute input/output rate. Here are some examples of the show interfaces output that I am referring to:

reliability 255/255, txload 1/255, rxload 1/255

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

I have personally used these to determine what is maxing out a router’s circuit and to see in what direction that traffic is flowing, but if you want to monitor for longer times and get detailed source and destination I would suggest you use IP Accounting
there some tools such as Cisco IP Accounting Fetcher and Net-Sense that will create reports from the information collected by IP accounting

Layer 1 network issues: Bad circuits or cables

Many times, the reason that users are complaining about performance is that there is a Layer 1 (Physical) network issue. For example, there is an issue with an Ethernet LAN cable or a T1 WAN connection. Errors that cause slow performance are especially common with WAN connections that span long distances.

The best way to check to see if your LAN or WAN connections are causing the slow performance you can use "show interfaces summary" command to see if you have dropped packets or errors

Errors and failure of the router hardware

While the show interfaces command might find issues with your connections, those errors could also be caused by your router hardware. For example, you could have a bad HWIC T1 card that is causing slow performance and causing errors to increment in the "show interfaces" output.

If this is a WAN circuit, many times, your carrier will assist you in testing and troubleshooting that circuit.

personally I'm a fan of AdventNet ManageEngine OpUtils this has been a tool I've liked for sometime and works well for having a single interface to many devices as it likely you won't just have cisco hardware.

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