Network Problems and Symptoms

[oighodaro1]

Hello Everyone,

This is my first post and I am hoping I have come to the right place. 

Background: I work for a non-profit and we are hoping to get new switches this summer. Our networking infrastructure consist of LAN and WLAN. We are currently using Cisco Catalyst 6509 for the LAN and Meraki APs for WLAN. 

Problems/Symptoms: 

We having experiencing different issues on different fronts. We are experiencing huge network slow downs when editing over the Network, the connections slow down almost to a halt.  Also whenever users attempt to download a file large than 100mb their download halts between 50 to 70 mb. Additionally the log is showing constant flapping. 

Log: has been attached.

some questions: What should I be looking for in the network connections ? Is the flapping causing the slow down ? 

Any assistance/help would be greatly appreciated.

Thanks

[Jon Marshall]

The outputs I asked for with the wired clients.

The 6500 outputs will be fine based on what you have already sent ie. I still need them but I will be able to tell what I need from them.

However the Dell screenshot you sent doesn't tell me what I need to know.

For the wired client port I need to see the STP settings which aren't shown in the screenshot.

Would it be possible to post the actual text configuration as you are doing with the 6500 ?

Jon

[oighodaro1]

My access to the Dell switches are very limited. I can't ssh into the console to get a low level access. The configuration screen is very limited.

I am using the Dell PowerConnect 2748. I have looked it up the Dell PowerConnect 2748 doesn't support STP.

[Jon Marshall]

I have just been rereading this post to make sure I haven't missed anything.

I noticed you said the Dell does not support STP but if the Dell is connected directly to the 6500 (via the patch panel) and the 6500 is reporting a TCN on the port connected to the Dell then it must be running STP in some form or another.

What is the make of the Dell switch ?

Jon

[chinpohpang851]

May I ask why there are VLANs name 3, 5, 7, 9 in this config?

[Skjalg Eggen]

the MAC flapping is where I would start to investigate. It seems fairly regular but not enough to be considered as a "full on" loop, which would grind your network to a halt. 

I would start to look for uplinks between switches that are unstable and flapping up and down, creating spanning-tree topology changes.

Know your interswitch uplinks, this is Key! you need complete control of these uplinks,

- which VLANS are allowed 

- which switches are connected to which switches

- speed and duplex

I would also look into what type of spanning tree your downstream switches are running, compared to the 6500's. Mixing spanning-tree types could be very bad. 

Check your network for HUB's! Yes, I know, we don't have HUB's in our network... 

but trust me I've hunted down quite a few hubs in customer networks where the owners laughed at the thought of there being HUB's in their network. those suckers hide quite well :)

I find that the process of elimination is quite effective in hunting down the cause of problems like these.

schedule a downtime for a few hours, then:

1. eliminate all switches and plug your computer directly to the firewall and check speeds and stability.

2. plug in the first switch and plug your computer into that and test the speed and stability

3. plug in the next switch and so on.

4 when you start experiencing the issues, you know it has something with the last switch you plugged back in.

5. Start to investigate that switch. 

      - what is plugged in there

      - is there anything plugged in-line from that switch to the previous switch, like say a HUB maybe         :)

good luck!

[oighodaro1]

AH!

I found 7 network HUBs and one of them is currently hosting all the network APs. Can you help me understand the effects of a HUB ? what type of problems would they cause ? 

Thanks

[Martin Carr]

Hubs are antiquated, and should not be used today under normal circumstances, they have no intelligence and flood frames received out all ports (except the one received on), it is also one collision domain.

Switches are intelligent and work at the data layer, they learn the MAC addresses from frames that traverse them, this information can be used to 'switch' frames out the interface to the destination host (instead of sending it to everyone) each port is it's own collision domain. These are just a couple of advantages.

With the above in mind and with the right configuration, hubs could cause issues such as flapping/looping, as from a switches perspective it appears as a host is reachable on multiple interfaces.

Martin