When 3 is NOT the magic number - using consumer grade switches/hubs in a school...

[Koldov]

Ok, I will preface this by saying my networking-fu is pitiful...

 

When I took over at my school we had just had a BSF refit of our network (cat 6, new switches etc).

 

However, one of the ICT suites was only given 6 network ports for a central pod with 8 computers on it... As I was just starting out in the job, I simply squeezed one of those computers inbetween a couple of others at the side of the room.

 

This still left 7, but I used an old consumer grade switch to split one port into two and it seemed to work fine.

 

A recent change in class sizes and teachers needing to use their own laptop instead of one of the pupil computers to do the teaching has led to me needing to put that computer back onto the central pod.

 

I simply moved the computer back into the space on the pod and plugged into the switch on the desk, unfortunately it wouldn't pick up an IP address. Rebooting everything seemed to make it work for a second or two and then got the old familiar yellow triangle and no network connection. It seemed to be that the last computer booted failed to pick up an IP address. I gave them all a static IP and rebooted everything but the same issue was still present, I tried various combinations of old switches and hubs and cables, but everytime one of the three would fail to connect.

 

These were various Linksys/Netgear switches or hubs, some Fast Ethernet (10/100), some Gigabit, some 4 port, some 6 port - it didn't seem to make a difference.

 

TL;DR

 

Am I missing something blatantly obvious - I can split the network port into two but not three?

[FN-GM]

There might be a limit to the number of mac address allowed on the port on the uplink switch you're connecting to.

[MatthewL]

If you take the switch out of the equation and plug the computer into the port direct does it work?

[chazzy2501]

Technician 101: Do not fudge something for people because you can. State that there is only 6 ports so only 6 PCs or they can get a networking guy back to do the job correctly. Unfortunately you've gone down the accommodation route (noob move) now you'll be fudging and making do then ultimately taking the blame when it fails.

 

oh, put the networks back to automatic, (manual entry typos are easy) yellow triagle can mean no ip, no internet, (different issues) if you assume that your always getting the same error you'll get stuckin a loop. Always with these problems is to remove everything do your steps 1 at a time and PROVE (to yourself) that every step is as you expect (no assumptions) (ipconfig each PC as you connect, ping 8.8.8.8)

[Koldov]

Thanks for all the helpful answers!

 

@FN-GM wins the prize of making me slightly less grumpy today...

 

Port security on the switches set to 2 devices according to our network support!

 

 

I didn't even know that was a thing! Drove me nuts most of last week in the middle of upgrading the ICT suite to Win 10, it was the last thing I needed....

[MatthewL]

I learnt something too today, didn't know you could do that.

[FN-GM]

Great news!

 

Port security should always be enabled to limit the number of Mac Addresses, even if it say 10. It will stop a a couple of attacks.

 

1. DHCP starvation - If you don't limit the Mac Addresses you can get some software to generate a new Mac and request new IP Addresses, it then loops around and des the same thing. Within 30 seconds or so it can use up all the addresses on your DHCP scope. This will mean legitimate clients won't be able to get an address.

 

2. Mac Address Table Overflow - Some other software can be used to fill the Mac Address table of the switch. When this happens the switch turns itself into a hub. When this happens they can they eves drop on the network and see the data.

Edited February 25, 2019 by FN-GM

[DrBeaker]

Technician 101: Do not fudge something for people because you can. State that there is only 6 ports so only 6 PCs or they can get a networking guy back to do the job correctly. Unfortunately you've gone down the accommodation route (noob move) now you'll be fudging and making do then ultimately taking the blame when it fails.

 

oh, put the networks back to automatic, (manual entry typos are easy) yellow triagle can mean no ip, no internet, (different issues) if you assume that your always getting the same error you'll get stuckin a loop. Always with these problems is to remove everything do your steps 1 at a time and PROVE (to yourself) that every step is as you expect (no assumptions) (ipconfig each PC as you connect, ping 8.8.8.8)

 

Any more Technician 101 tips to share? I'm always interesting to hear other techie war stories etc. My daily mantra is USERS LIE!