Question about Cisco Catalyst 3750G-24T SMI (WS-C3750G-24T-S) 24x1000 Mbps Networking Switch

1 Answer

Unexplained network problems.

Our network core is all Cisco 3750G-24T switches. They had no configuration, the original IOS (c3750-i9-mz.121.14-EA1a) and we just plugged them in and they worked. In the past few months, we've been having intermittent network issues. Half the building would have horrible latency or won't be able to access the network at all. Looking at bandwidth graphs shows you that not more than 10 megabits of our gigabit connection between switches is used. We've put passwords on the switches, reconfigured all links to ensure they are gigabit and to reduce hops between devices. We've also updated the IOS on one switch as a pilot and are running Cisco network assistant to visualize the network. We have yet to identify what was happening, or determine if it will happen again. What does your organization do to prevent this kind of problem? Thanks in advance for the advice!

Posted by on

  • 2 more comments 
  • joeyd666 May 27, 2009

    Hi Brad,



    Thanks for taking the time to check this out. Currently we have 1 VLAN and all users are on it. Also, the included image is our network. the caution and emergency icons are not problems. they have been resolved but the log of them was not removed.



  • joeyd666 May 27, 2009

    I uploaded a higher resolution graphic of our network and included show tech output.



    http://www.mediafire.com/download.php?lz...

  • joeyd666 May 29, 2009

    Hello,



    Sorry for the delay. we have approximately 200 users at any given time on a single VLAN. Unfortunately, Cisco Network Assistant is the only program we have that will map out our devices at the moment. Our Layer 3 is a single class B subnet at the affected site. There should be no routing other than with our default gateway.



    As for frequency, this occurs several times a month and lasts anywhere from 15 minutes to several hours. We've been unable to determine any abnormal CPU load or Bandwidth usage during an event. In fact bandwidth is often below 10Mbps during these situations according to cisco's stats. We also have a machine running NTOP on the main switch monitoring VLAN1 and that sees no major bandwidth usage over 15mbps most times. Most of our links are gigabit.



    You've brought up a few other good questions and I will see what I can do to answer them ASAP. In the mean time, can you suggest a sniffer if you don't use NTOP?

  • joeyd666 Jun 12, 2009

    FYI, I believe we found the problem. checking the logs again while experiencing the issue, we noticed a lot of host flapping. We were unable to resolve why this was occuring until Cisco Network Assistant showed a network loop for approximately 5 seconds. We were able to get the port numbers and located an old WAP11 everyone had forgotten about. Somehow it was malfunctioning and acting as a bridge, causing a network loop. This device was at the far end of the building so it only connected with another wireless device sporadically. Half of the building was going from 1Gbps to 11Mbps, causing major congestion.

×

1 Answer

  • Level 2:

    An expert who has achieved level 2 by getting 100 points

    Hot-Shot:

    An expert who has answered 20 questions.

    Corporal:

    An expert that has over 10 points.

    Mayor:

    An expert whose answer got voted for 2 times.

  • Expert
  • 63 Answers

Hello,
I would be glad to help with this.
How many VLANs do you have? How many users per VLAN? Do you have a generic diagram (stripped of all company info) that you can share? Can you send me a "sh tech" from the core switch so I have a better feel for how things are configured?
Thanks!

Posted on May 27, 2009

  • bradhscherer
    bradhscherer May 28, 2009

    Hey Joey,

    Thanks for all the detail. Ok...so I have a few questions.
    How many users again on VLAN 1?

    Do you have a better diagram than Visualizer? I think I understand it but I hate the way Visualizer draws it. Do you have a Visio? Can you hack one together real quick? I need to see layer 2 & 3.

    How often is the latency?
    How long does it last?
    Do the logs on any device show anything?
    Can users ping their default gateway during latency?
    Can users ping through the default gateway?
    Can they ping each other on the same switch without latency?

    There are many many things that could be at play here. Including broadcast storms, rogue backups, virus scans, automated client patch rollouts, spanning tree, convergence, a device doing snmp queries to often etc.

    I would recommend upgrading to at least Maintenance Release 19 for your train of IOS to eliminate any software issues. It should be relatively painless.

    We use tools like Netscout Performance Manager, PRTG, Sniffers etc to keep a good eye on things. We have had many issues like this and more often than not it wasn't the network gear at all.

    The best thing to do is get a sniffer to analyze the traffic.

    Knowing more about the latency conditions and understanding your topology better will definitely help me help you better.
    And...dont worry you will get through this!!!

  • bradhscherer
    bradhscherer May 29, 2009

    Despite all the fancy sniffers and big money products....Wireshark is still my de facto sniffer and I use it all day everyday. It is very versatile and FREE!

×

1 Suggested Answer

6ya6ya
  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi,
a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
goodluck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%

my-video-file.mp4

Complete. Click "Add" to insert your video. Add

×

Loading...
Loading...

Related Questions:

2 Answers

Running BGP on WS-C3750X-24T-S using IP Services IOS?


http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/15-0_1_se/release/notes/OL25302.html

Apr 29, 2015 | Cisco Catalyst 3750X-24T-S Layer 3 Switch...

1 Answer

Cisco 3750 web config


Yes, know more about the Cisco 3750, just visit: http://www.3anetwork.com/cisco-catalyst-3750-switches-price_c41

Dec 26, 2013 | Computers & Internet

1 Answer

Catalyst 3750 keeps rebooting with an error message platform-1-crashed


Contact Cisco support for a replacement. It is not normal for a switch to reboot like that. Cisco switches (not routers)have a lifetime warranty

Mar 12, 2012 | Cisco Catalyst 3750 24 10/100 + 2 SFP...

1 Answer

Can a 3750G run 1000bt service of its electrical port? Thanks


HI,
The cisco 3750G-24T is a 24 port 10/100/1000Mbps switch.
If your connected device ( PC/Laptop) is having a Gig NIC card then the switch port will negotiate the speed and will establish for 1000Mbps link.

I am little curious about your word 1000bt . is it 1000bps i.e 1Mbps or you are looking for the connetcion of 1000Mbps i.e 1Gbps

Best Regards

Oct 20, 2010 | Cisco Catalyst 3750G-24T SMI...

1 Answer

Ports 1-8 are working. all others are dead. loaded newest ios but still only 8 ports available. thanks JJ


Contact CISCO, and get an RMA (Return Materials Authorization) to ship it back to CISCO, for repair/replacement.

Nov 13, 2009 | Cisco Catalyst 3750G-48TS

1 Answer

Need to locate PC's on our network, accurate to the switch port.


If its not to many computers , tone out the lines with a network toner

Jul 06, 2009 | Cisco Catalyst 3750G-24T SMI...

Not finding what you are looking for?
Cisco Catalyst 3750G-24T SMI (WS-C3750G-24T-S) 24x1000 Mbps Networking Switch Logo

324 people viewed this question

Ask a Question

Usually answered in minutes!

Top Cisco Computers & Internet Experts

Doctor PC
Doctor PC

Level 3 Expert

7733 Answers

Prashant M
Prashant M

Level 3 Expert

2260 Answers

brian soufane

Level 3 Expert

693 Answers

Are you a Cisco Computer and Internet Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides

Loading...