Learn how to a build a cloud-first strategyRegister Now


Ping Latency Issues on hosts connected through 3550 Cisco Switches

Posted on 2007-10-19
Medium Priority
Last Modified: 2010-05-19
Hi All Please observer the following illustration:

Linux Host A ---Path A---Cisco Switch 3550 on Rack A---Gigabit Path B---Cisco Switch 3548 on Rack B---Path C-- Linux Host C

The thing is that I am concerned about the ping latency when pinging from host to host and from host to switches please consider the following :

I used ping -c 100 -s 1024 hostIP to get the data below

Case A : From Host C to Switch B         min/avg/max/mdev = 1.884/2.676/14.752/1.865 ms
Case B : From Host A to Host C            min/avg/max/mdev = 0.825/0.901/1.027/0.046 ms

Note that a ping from Host C to Host A has to travel through Switch B then Switch A and then reach Host A and backwards, while a ping from Host C to Switch B has only to travel to Switch B  and back "the same ethernet segment" so how can it be that that the average ping of case A took more than the average ping of Case B although the round trip time of Case B is shorter and they both travelled through the same paths.

Case C: From Host A to Switch B      min/avg/max/mdev = 2.248/8.730/56.952/13.380 ms

Now in this case the round trip time from Host A to switch B (Case C) is shorter than the round trip time from Host A to Host C (Case B). However Case C has an higher average time than Case B.

How can this be ?

The only thing that I might think about is that it has to have something to do with the CPU of the Switch but i do not know what exactly..

Question by:http:// thevpn.guru
LVL 50

Accepted Solution

Don Johnston earned 2000 total points
ID: 20109021
>The only thing that I might think about is that it has to have something to do with the CPU of the Switch

You're correct. Switches are designed to forward frames as quickly as possible. Since only source and destination MAC addresses checked (by ASIC's), the frames are forwarded very fast.

When you communicate with the switch itself, it (the CPU) will have to do more work. The CPU's in these switches aren't the optimized for this type of operation.

Expert Comment

ID: 20109195
Is there a VLAN infrastructure and are the Cisco devices and Linux hosts in diferent VLANs?
LVL 19

Author Comment

by:http:// thevpn.guru
ID: 20109236
Nope, default VLAN settings..

Expert Comment

ID: 20124274
donjohnston is right on. Ping generally should not be used as a tool to measure performance (i.e. response time) reliably, but simply as a tool for verifying reachability which is what ping was created to do.

Featured Post

 The Evil-ution of Network Security Threats

What are the hacks that forever changed the security industry? To answer that question, we created an exciting new eBook that takes you on a trip through hacking history. It explores the top hacks from the 80s to 2010s, why they mattered, and how the security industry responded.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This tutorial will go through the steps required to write a script that will back up the configuration settings of a HP-ProCurve switch. You will need to get the following things to follow this tutorial: Telnet Scripting Tool e.g. TST10.exe …
Hello All, I have been training on Multicast for a while now and whenever I start the topic , I find out that my friends /  Colleagues mention that they do not know how to test Multicast Joins. As most of the multicast would be video traffic and …
this video summaries big data hadoop online training demo (http://onlineitguru.com/big-data-hadoop-online-training-placement.html) , and covers basics in big data hadoop .
If you're a developer or IT admin, you’re probably tasked with managing multiple websites, servers, applications, and levels of security on a daily basis. While this can be extremely time consuming, it can also be frustrating when systems aren't wor…
Suggested Courses
Course of the Month21 days, 3 hours left to enroll

810 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question