Bandwidth Testing on 3560 Switches

richard.kane · ‎01-03-2009

We are having problems with throughput on 3560 switches and I am looking for a way to evaluate the actual speed of gigabit links between switches. It looks like ttcp does not work properly for gigabit or else I don't know how to read the results. Is there another way to do it?

ropethic · ‎01-03-2009

This depends on quite a few variables:

1. What is the appliaction

2. Latency betweem two switches

3. packet queueing enabled

4. packet sizes?

Place as sniffer on one end to a SPAN port and to get a view of the traffic. Look for retransmissions, tcp window errors, etc.

Unfortunately you will need to dig a bit deeper to find a cause.

cisco24x7 · ‎01-03-2009

Iperf is a much better performance testing tool.

richard.kane · ‎01-05-2009

Thanks; it seems very good.

richard.kane · ‎01-05-2009

Thanks for the reply.

What is packet queueing?

Why the SPAN port with a sniffer? Doesn't the switch report all of those errors?

ropethic · ‎01-07-2009

Please see url for explaination of different queue methods

http://www.cisco.com/en/US/tech/tk543/tk544/tsd_technology_support_protocol_home.html

Settting a span port to the sniffer will allow you to analyze the conversations traversing your link. The switch will not report Layer 4 errors. Users establish connections using TCP where each segment is assigned a sequence number. if packets are being delayed or dropped a retransmission will occur. The sniffer will identify these as retransmissions.

You can get wireshark sniffer for free.

cisco24x7 · ‎01-07-2009

Wireshark is a good tool for viewing output file. In a production environment where you

you have to view Gigabytes of data, I would

suggest you build yourself either a OpenBSD

box or Gentoo Linux box and use tcpdump for

this purpose. Tcpdump is best, bar none.

my 2c