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Preventing network loops

B

Brujah-99

Weaksauce
Joined
Jan 7, 2005
Messages
71
I've had a couple of people at my office plug two ends of a network cable in to the same dumb hub causing all sorts of problems. It's my understanding that spanning tree is supposed to prevent that sort of thing and I do have it enabled on my core switches. Aside from not letting anyone plug in new lan cables are there any proactive steps I can take to prevent this from happening in the future? Thanks for any advise.
 
Brujah-99 said:
I've had a couple of people at my office plug two ends of a network cable in to the same dumb hub causing all sorts of problems. It's my understanding that spanning tree is supposed to prevent that sort of thing and I do have it enabled on my core switches. Aside from not letting anyone plug in new lan cables are there any proactive steps I can take to prevent this from happening in the future? Thanks for any advise.
Click to expand...

Make an example of a user. Beat them with a cat5 cable.

When you are done, stick his/her head on a spike out front of your office.
 
The best thing to do is get rid of the hubs and put in switches that support spanning tree. Cisco switches, in particular, have a "PortFast" feature used on ports that connect to end-systems (pc's, desktops, printers, etc) which pushes the port into the Forwarding state quicker than normal so things such as DHCP requests and domain logins do not fail. If a port with PortFast enabled detects a BPDU (a frame circulated throughout the L2 network as part of the spanning tree process) it will bring down the port. This would likely help your problem. I know some other switches besides Cisco have features similar to PortFast, but I can't speak as to whether they do the same thing, or if they simply disable spanning tree on the port (a bad thing).

The larger problem is: why do your users have access to your hubs? This presents a security issue in addition to the connectivity issue you're currently facing. The hubs should be secured in a place that only you and the owners of the company can access.

That is my take on it.
 
I know companies who do not use Patch Panels because they are to easy for anyone to pull plugs and put them elsewere. What they use is 110 Blocks. You would need a punch down tool. THis keeps all the Network changes all up to you and nobody else.

Merc did this with all their offices and swears by it.

So hub or switch to punchdown block to drop down.
 
did you find that some of your managed routers put its ports into error mode due to loop?

Not all offices can have 1 cable per PC and not all offices can have a lockable area to put their switches in.

eg

I have a cable per room and a switch at the end. Its a pain, i know and I would love to have a switch per floor and a wallbox per computer but its just not possible in this area.
 
Boscoh said:
The larger problem is: why do your users have access to your hubs? This presents a security issue in addition to the connectivity issue you're currently facing. The hubs should be secured in a place that only you and the owners of the company can access.
Click to expand...

XOR != OR said:
Make an example of a user. Beat them with a cat5 cable.

When you are done, stick his/her head on a spike out front of your office.
Click to expand...


As above 2 posts mention....here's the issue. Granted getting hardware that will deal with the loop issue may alleviate this issue for you..but in this situation...you're spending money to support end users having free reign of your network. Time for stern rules to be put into place...and consequences. And perhaps...if you're going to spend money..get small locking cabinets to put your switches in.
 
Thanks for the replies. I'll look in to the portfast feature to see if there's anything simlar on our switches. As for the security issue, in most cases my users don't have access to switches or hubs. Unfortunately we have conference rooms that fill up with people with and only two network jacks. :(
 
Make an example of a user. Beat them with a cat5 cable.
Click to expand...

Haha in the old days there was "Cat o' nine tails" but today its the dreaded"Cat o' six tails"
 
Brujah-99 said:
Thanks for the replies. I'll look in to the portfast feature to see if there's anything simlar on our switches. As for the security issue, in most cases my users don't have access to switches or hubs. Unfortunately we have conference rooms that fill up with people with and only two network jacks. :(
Click to expand...

Put up a sign that says something like "Hey asshole! Don't plug both network jacks into a hub or switch, only use one!"
 
I seen a switch locked up in a chicken-wire cage once for this very reason.

I shit you not LOL

YeOldeStonecat said:
As above 2 posts mention....here's the issue. Granted getting hardware that will deal with the loop issue may alleviate this issue for you..but in this situation...you're spending money to support end users having free reign of your network. Time for stern rules to be put into place...and consequences. And perhaps...if you're going to spend money..get small locking cabinets to put your switches in.
Click to expand...
 
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