Discussion on:

The 10 most common causes of network slowdowns

How many of these problems have you encountered on your network? Can you add some other performance-killers to the list?

Other problems can include a virus, an DoS attack on the company firewall(s) (seen this!) and an e-mail system that is sending a mass mail with large attachment, failing then attampting retry.

this occurs when users attempt to add addititional devices

We use Cisco's BPDU Guard for all user ports on our Cisco switches. This ensures that no network device is used. If you attach a network device to these ports, then the port shuts down and must be reactivated by a network administrator.

Works like a charm and keeps any users from causing loops!

http://articles.techrepublic.com.com/5100-1009-6154589.html

It includes BDPU guard and much more for a reliable switching infrastructure.

But I see you've already been there .

Does this command work on all Cisco Switches?

I have some older 2900XL/3500XL series stuff!

Thanks

Got called out to a site that was getting sporadic slowdowns throughout the day, to the point of saturating a T1. Turned out to be an outside contractor who, during his slow moments, would hook his personal laptop to an open port in a spare office. All fine and dandy except for the P2P file sharing app that was moving video files.
The thing that impressed me was that when I blocked his IP to track down the offender (Let's see who complains that their internet just went down...) the app, after a couple minutes of getting no response, dynamically changed the unit's IP address, reconnected, and started happily chugging away again.
The local IT has since been advised to physically disconnect the drops in any unused offices. Not sure what happened to the contractor.

Our biggest problem with outside vendors is them slapping in an unmanaged mini-hub or worse, improperly configured wireless router.
Then you get to plan hide and seek to find the physical location of the thing cause no one ever knows anything about it or how it got there!

I've seen it happen a few times where an office will have both both hard-wired and wireless networks. Someone will turn on or forget to turn off the wireless card on a laptop and it will be connecting to the network via both connections.

We don't use wireless so it's not an issue for us but I know of a few IT contacts that have run into this.

How bad is it to use both wireless and wired at the same time? Its what our boss does because he doesn't want to have to remember to shut one or the other off. We're just a 20 person workgroup network, but I've always been curious: how can I go about and see if a user having two ips (one for wireless, one for wired) will affect their performance/bandwidth?

You can't use both at the same time. It's possible to have both interfaces on and connected, but the system will default to route traffic from one or the other and usually will/should prefer the wired interface. You need EtherChannel drivers on similar card types to do channel bonding and link aggregation.

if you use a Virtual Machine within the Physical Machine!

If you got a virtual machine inside, it counts as a second PC.

It is possible to use 2 Ethernet ports if without EtherChannel if you're connected to two subnets and you want to manually input a bunch of routes and turn your PC in to a complex router. That lets you talk to different destinations at the same time but it's a nightmare to manage.

Had a situation where a sales group on the "other" side of the corporation brought in an outside vendor with a product solution and installed it without IT oversight. Vendor refused our access to computers after installation and refused installation of virus protection software. Sales force used software, along with the required internet connections, and obtained trojans that slowed network down to a crawl. The problem was made worse by the vendor insisting it was not their systems causing the problem. Demonstrated their error by disabling network access to those computers, and Lo and Behold! the network returned to normal!

Architect is a noun, a person who designs, typically buildings and landscapes. You cannot really architect something. You design something. Perhaps you meant a well designed network? As a Florida registered Architect, I find the improper use of the word architect by many IT types, as strange at best. The IT industry is full of extremely intelligent people and to misuse a word like this is egregious.

-VERB
To plan, organize, or structure as an architect: The house is well architected.

the word. Let's take an exapmple of Engineer, thus: The machine is well engineered. Sounds okay; what about doctor? You say "the patient is well doctored"?

"doctored" can be appropriate. Those papers were doctored.

It's amazing the amount of places I see that still use hubs. And sometimes the network guy doesn't know the difference between a hub and a switch.

Bin those hubs and replace with switches.

I have found that it is pretty straight-forward to identify any of the 10 items listed as the culprit when the problem is isolated to just one of the 10 causes. However, when it gets really fun is when it is a combination of more than 1 of the ten and some moron is trying to figure it out.

I recently had a twist on 1, 2, and 3 where the client used a big name firm from the other side of the state to install $25 daisy-chained switches throughout their production work area onto a combined Win-Linux network. The customer's cue-to-call in for help was it was taking 15 minutes for color print jobs to reach the printer's output tray. The customer had their big-firm, non certificated specialists come in-2 hours of drive time each way-in tandem because one "specialist" was obviously not enough horsepower to troubleshoot the problem. They came and scratched their heads on Friday and again all day Saturday (weekend rates!) They also hauled the printer's manufacturer technician/specialist at $200/hr, min. 2 hours, in on the weekend to troubleshoot his "broken equipment" only for all to leave without resolution except finger pointing to each other.
I happened to be on the site Monday morning when the owner of the business said "you know how to troubleshoot these issues. We have already spent well over a thousand dollars and still no resolution and we still can't print in color!" He asked me to clear my evening schedule because he expected a full network rebuild and wanted me to do it rather than his IT Department's outside firm.

I said, why not take a quick look at it now. I went to the daisy chained switch and noted that it had a bank of green lights and one orange one (a Clue!) I traced the orange one to a mis-configured, half duplex PC NIC, reset it, the light turned green and I said "have your people try to print now." The big-named firm sent back a kid (4 more hours of drive time) to confirm that the staff could really print, but when I bumped into him he said "You got lucky pal, but I still think the NIC on the printer is bad and so does everyone in my firm!" That was three weeks ago and the firm from the other side of the state is still blaming the printers manufacturer. The funny thing is everyone can print in color and the problem hasn't resurfaced, but they have a Full Network Rebuild on their to-do list.

Although that firm's ego is still preventing them from admitting that they really missed some obvious clues, their lessons should be:
Consider the big picture, look for the warning lights-they generally mean something, use quality enterprise hardware, don't assume that it is automatically someone else's fault, and be willing to admit when you are wrong.

Oh, and try to have fun in your work.

Number one slowdown on networks is duplex mismatch.

This is not even mentioned.

If you are talking small networks,adding(cascading)switches causes very little, if any propgation delay.

So I don't quite get that one.

Screwing up a subnet mask is also another gotcha.

Cheap switches can also cause issues if they can'y auto negotiate correctly.

DNS servers?
What is this,a windows only seminar?

Their are other,better methods for nework discovery(SLP being one).
Netbios broadcasts and WINS suck,but if you are running M$ based garbage,you get what you deserve.

Top 10,maybe a couple of obvious ones,but there are loads of others depending upon the size of the network.

I kid you not.
Friend of mine was the IT guy for a polytechnic in the early 90's and found that two PCs wouldn't run at the same time. Turned out that the Taiwanese NIC maker had been creating duplicate MACs and the training institute was unlucky enough to end up with two of these cards on their LAN