slow network connection suddenly

[Clkj]

Hi everybody,

 

Im a relativly new technician and have a job at a primary school as there main technician.

 

Basically everything was working fine yesterday then overnight its not. I got a phone call earlier saying the internet isnt working. When i got there i found out a few computers are working fine and all the rest are not. They have a really slow network connection and internet connection or sometimes no connection. Ive attached a basic plan of everything below.

 

 

For some reason there is a computer in the main building that seems to be patched at cab 1 (no idea why - its quite an old building though) Everything connected to cab 1 works fine. Cab 2 onwards is when it gets slow. So im asuming its something to do with the main link? The two main buildings are connected via an ethernet connection BUT the cable goes into what looks like a fibre box which then goes into another smaller box (Via fibre) which then goes into the switch via ethernet (Ive never seen this set up before)

 

I havnt gone in today really to try anything - but it obviously needs to get working tomorrow so thought id come on here to get some more ideas as to what it would be.

 

Thanks for any responses.

[SYNACK]

Could be a fibre media converter, have you tried rebooting the switches and converters, if they are managed you could try to log into them to see if there are excessive error on the fibre link, those converters do burn out.

[Clkj]

The first thing i was going to do tomorrow was a reboot. I dont know any of the IP addresses of the switches are managed. The whole network was basically left in a really big mess!

 

If its the fibre burning out - would it be possible to ditch the fibre bit and just plug the ethernet in? for a temporary period atleast? The mian office and admin area is one that is affected so i need to get them on somehow?

 

Thank you for the quick response.

[SYNACK]

The first thing i was going to do tomorrow was a reboot. I dont know any of the IP addresses of the switches are managed. The whole network was basically left in a really big mess!

 

If its the fibre burning out - would it be possible to ditch the fibre bit and just plug the ethernet in? for a temporary period atleast? The mian office and admin area is one that is affected so i need to get them on somehow?

 

Thank you for the quick response.

 

Not good from an electrical point of view but yes, you should be able to yank the fibre and connect via copper as long as the cable run is less than 100m which should be good for testing. If it is that I'd replace the fibre converters though, they are not that expencive and you may be able to replace 100mbit ones with GBit depending on what is there already.

[Clkj]

Okay - This seems very likely.

 

With the media converters - it converts an ethernet to fibre? but from what i remember the connection between the buildings are still ethernet - i may have that wrong it was only a quick check. i havnt got a cable long enough to replace the whole main cable?!?

 

Im really new to this ive only been a technician for a few months. This is why there are so many questions!

 

I thank you agian for your help.

[twin--turbo]

Is there a copper link and a fiber link running between buildings at the same time?

 

What are the lights doing on the switch gear? are they battering away like hell? If this is the case then you probably have a network loop. ( little darlings in the classroom may have linked a pair of outlets.)

 

Rob

[Clkj]

I havnt looked at the switches today. I havnt managed to get in as i work at 2 schools and today was my day at the other school which i couldnt leave.

 

I have no idea whats connecting the two buildings together now. all i know theres 1 blue cable i can tell tomorrow is going to be stressful.

 

Thanks again everyone.

[SYNACK]

Your diagram was a little perplexing, from what I could gather it seemed to indicate that there was both fibre and a copper link between the buildings, that one random PC. You'd use that link and plug that into the other switch. It is common for copper links to still exist if a school has moved to fibre later.

 

You are right about the converter, it just takes a ethernet cable and converts to fibre, one of those at each end and you can use fibre transparently to cheaper switches, they don't know the difference. The usually look something like the white box here:

[Clkj]

It does look like that but theres 2 boxes at each end with fibre. That little box is connected to a bigger box which is connected to the link.

 

And yes your right! (I think) there is a computer which is connected via a copper link to cab 1. Im assuming it must be as its the only one in the other building working and its 100% not patched at the cab in the same room as it. so if i connect this to the switch in the room i have a connection - if this works then its more than likely the fibre converter.

 

Thanks again!

[SYNACK]

Is there a copper link and a fiber link running between buildings at the same time?

 

What are the lights doing on the switch gear? are they battering away like hell? If this is the case then you probably have a network loop. ( little darlings in the classroom may have linked a pair of outlets.)

 

Rob

 

Good call, I had not thought of that, OP should give these a read to get some more insite into that fault:

Possibly a loopback that someone has created accidentally on your network of a faulty network card somewhere. These threads may help:

 

http://www.edugeek.net/forums/networks/19195-solved-entire-network-down-100-network-utilization-please-help.html

http://www.edugeek.net/forums/networks/23282-arp-flood.html

http://www.edugeek.net/forums/networks/6306-stop-looping-effects-caused-interconnection.html

[SYNACK]

It does look like that but theres 2 boxes at each end with fibre. That little box is connected to a bigger box which is connected to the link.

 

And yes your right! (I think) there is a computer which is connected via a copper link to cab 1. Im assuming it must be as its the only one in the other building working and its 100% not patched at the cab in the same room as it. so if i connect this to the switch in the room i have a connection - if this works then its more than likely the fibre converter.

 

Thanks again!

 

You want to make sure to disconnect the fibre if your patching it in that way as you don't want two active links at the same time as that would cause the loopback stuf meantioned above.

[Clkj]

Okay - Good job you mentioned that as i probably wouldnt have! (Your probably all wondering why im an IT technician now)

 

Ive read some of the posts on the threads you said to look at - gave me some more ideas. Just incase none of this works can you think of anything eles? Its strange because it sometimes works just very very very very slow. For example i can remote from building 2 to the server in building 1 sometimes but its so slow the connection drops before i can even type something.

 

Thanks again for everything.

[SYNACK]

Nothing else comes to mind at the moment, are you sure its a fibre link not some kind of wireless or phone company link or something weird, that sounds like some very nasty slowdown that should not be present on a 1GBit link, if your fibre is 10 or 100mbit it might explain some of it though.

[twin--turbo]

If there are no apparent network loops and after a reset of the network gear then next call is to disconnect each distribution switch in turn and see if the problem goes away, if you can pin the source of the issue to a particular switch you can then unplug each port until you find a rouge device. if no rouge devices are present then the switch may be faulty.

 

We once had a PC who's ether port was faulty and causing massive amounts of broadcast data across the network.

 

One other thing to consider, if the fiber converters are in an open area then someone may have been playing with the dip switches that are common on these devices. If there is a speed or duplex mismatch then you will have some dreadful performance.

 

Rob

[Clkj]

Nothing else comes to mind at the moment, are you sure its a fibre link not some kind of wireless or phone company link or something weird, that sounds like some very nasty slowdown that should not be present on a 1GBit link, if your fibre is 10 or 100mbit it might explain some of it though.

 

I think its fibre! Its defernatly the cable connecting both together. It looks like an ST connector on one end.

 

I thought it was strange though. Yesterday when i left it everything was fine, this morning when they got there nothing worked but the building with cab 1 in. I was just trying to think of what could have happend overnight to cause this. Its not a complete drop in connection because you can still connect just very very very very slowly!

[Clkj]

If there are no apparent network loops and after a reset of the network gear then next call is to disconnect each distribution switch in turn and see if the problem goes away, if you can pin the source of the issue to a particular switch you can then unplug each port until you find a rouge device. if no rouge devices are present then the switch may be faulty.

 

We once had a PC who's ether port was faulty and causing massive amounts of broadcast data across the network.

 

One other thing to consider, if the fiber converters are in an open area then someone may have been playing with the dip switches that are common on these devices. If there is a speed or duplex mismatch then you will have some dreadful performance.

 

Rob

 

Thanks - i will try this also. I do have a spare switch which could replace a faulty one. i have no idea what dip switches are but there not in an open area so i hope nobody has done anything to them! ill look into that aswell!

[twin--turbo]

DIP switches are small switches on devices, not common these days but still seen on media converters to configure speed/duplex etc.

 

Rob

[Clkj]

Quick update - Ive found a temporary fix but i dont understand what ive done to fix the WHOLE network (I just thought it would fix the office computers)

 

 

As you can see. I used the old copper connection to try and get the 2 office computers working and unconnected link 1 - thinking this would only get the office working along with the IT suite. But everything worked after disconnecting link 1 and connecting the old copper link. So from what i can work out the fibre is working.

 

Could a dodgey cable on link 1 have caused this the whole network to stop - apart from the computers connected via switch 1? or do you think ive somehow disconnected a loop by taking out link 1? if i have i have no idea what loop - it must have something to do with old wireing.

 

(all the yellow and red lines are parts of the network not working yesterday - the green ones were working)

 

Thanks again for all your help.

Edited July 6, 2012 by Clkj

[SYNACK]

Quick update - Ive found a temporary fix but i dont understand what ive done to fix the WHOLE network (I just thought it would fix the office computers)

 

[ATTACH=CONFIG]14541[/ATTACH]

 

As you can see. I used the old copper connection to try and get the 2 office computers working and unconnected link 1 - thinking this would only get the office working along with the IT suite. But everything worked after disconnecting link 1 and connecting the old copper link. So from what i can work out the fibre is working.

 

Could a dodgey cable on link 1 have caused this the whole network to stop - apart from the computers connected via switch 1? or do you think ive somehow disconnected a loop by taking out link 1? if i have i have no idea what loop - it must have something to do with old wireing.

 

(all the yellow and red lines are parts of the network not working yesterday - the green ones were working)

 

Thanks again for all your help.

Could be a dodgey link but more likely you've inadvertently disconnected a loopback. If I was you I'd try to document exactly how all the different switches are connected together as a starting point to get to know the network better and understand it more.

[twin--turbo]

was the copper connected before?

 

Rob

[Clkj]

was the copper connected before?

 

Rob

 

No it wasnt connected before. All i did today was unplug link 1 and plug in the copper connection to switch 1 and the whole network went back to normal.

 

I agree with what you say. The person taking care of the network before me didnt document anything or keep any records of anything. When i started all they passed on to me was the administrator password. None of the teachers laptops or office computers are actually on the domain there just stand alone computers.

 

Most of the network is on the way out. i have 3 new managed switches to replace 3 of the old netgear ones. a whole new set of desktops and laptops and liceses for Windows 7. (Currently on XP). So as of the summer holidays most of it will be started from scratch anyway. (and everyone will be on the domain!)

 

Thanks for all your help.

[Michael]

It does look like a fibre fault or indeed a duplex mis-match. Personally I try and avoid media converters, as it's one more link in the chain to go wrong. Installing fibre modules, such as a Cisco GLC-MM-SX will give you a dedicated 1Gbps link over OM1, OM2 or OM3 fibre and allow you to manage it properly both ends. All major manufacturers adhere to this standard.

[Clkj]

It does look like a fibre fault or indeed a duplex mis-match. Personally I try and avoid media converters, as it's one more link in the chain to go wrong. Installing fibre modules, such as a Cisco GLC-MM-SX will give you a dedicated 1Gbps link over OM1, OM2 or OM3 fibre and allow you to manage it properly both ends. All major manufacturers adhere to this standard.

 

Yeah its looking likely to be the fibre. whole network went agian today apart from the 2 switches that are not connected via the fibre. I didnt have time to do alot of testing today but im planning on connecting all 4 switches together not through the fibre and seeing if it works. If we get back up and running then im assuming its the fibre. I also want to test if 2 computers can communicate on the switches that arnt connecting the the network (if that makes sense) to rule out problems with the switches.

 

Working at 2 schools means i dont have alot of time when something like this goes wrong. I cant leave one school to go to the other as im on 2 seperate contracts for each. Meaning it just has to wait which isnt great.

[Clkj]

It was one of the media converters by the way!

 

Thanks for everyones help.

[plexer]

Did you only replace one?

 

I'd recommend replacing both especially if you didn't get the exact same make/model as a replacement.

 

Ben