Switch - Cant obtain an IP address

Playboy

Ok so here is the problem. Im living on a University Campus and I connect to the internet through their network from my room. I have to register my mac address with them before I can access the internet. I have a laptop and and a desktop and I used to use both from the connection with a switch. I had to register both mac addresses with the IT services before I could go online with either.

When I first bought a switch I just plugged it in and it worked fine. After a couple of days the power died in the flat and when I booted everything back up the I couldnt obtain an ip address on either machine through the switch. I returned the switch and got a new one and this worked fine out of the box.

So I moved to a new room on campus after a couple of months and my pc got damaged so I had to replace the motherboard. I decided to do a full upgrade while I was at it and it took me a few weeks so I relied on my laptop connected directly to the wall and not through the switch for my internet. When I finished upgrading I registered the new mac address with the IT services.

Now both my laptop and destop connect to the internet when connected directly to the wall socket and not the switch. When both are connected through the switch only the desktop connects to the internet. The laptop cant obtain an IP address. So I connect the laptop to the wall directly and I copy the values from ipconfig/all and configure the laptops ip, gateway, dns etc manually. I connnect the latop back through the switch my laptop says it is connected but I cant access IE or msn, skype etc. My desktop still connects fine through the switch though.

I have tried swapping the cables .. turning off the switch for a few hrs to no avail. There is no reset button on the switch. Am thinking of buying a new switch but they arent cheap and I would rather not.

Thx guys

ethernet

Do switches have MAC addresses also? If so, register that as well.

I don't advise you copy the values from ipconfig from one machine to another as setting both to use the same IP address will cause a conflict.

Playboy

ethernet wrote: »

Do switches have MAC addresses also? If so, register that as well.

I don't advise you copy the values from ipconfig from one machine to another as setting both to use the same IP address will cause a conflict.

Hi ethernet. As far as I am aware I dont think switches have a mac address. I didnt copy the values from one machine to the other .. what I did was to obtain the values from the laptop when connected directly to the wall socket and online .. and replace the assigned 169 IP address when the laptop cant obtain an IP address when connected through the switch. I hope that clears it up a bit .. sorry for the confusion

Snowbat

Before you do anything else, contact IT services, tell them what you told us and ask if this should still work.

They may have made changes to their DHCP setup that would prevent IP addresses being assigned to *both* of your MAC addresses if they're on the network at the same time. For instance, if they've mapped both MAC addresses to a single IP address, trying to connect both machines concurrently would cause an IP address conflict and one connection would stop working.

Playboy

Thx Snowbat .. will get in touch with them

Playboy

Ok after a long wait for a reply .. this is what I was told.

"Due to some hacking activity early this year we implemented a feature on the switches which limits the ports to only switch traffic to/from a single mac address. The nature of the hacking/attacks used spoofed virtual mac addresses to impersonate valid machines with the intention of stealing login info etc.

So, no, as it stands you can only use one PC on a port at any one time.

(however ... a savvy user might share a 2nd computer through another network adapter on the first (NAT) )"


So it looks like there is a way around it .. but I dont really understand what he means? Any help guys?

Snowbat

He is hinting that if one of your machines has two network interfaces, you can use internet connection sharing:
http://support.microsoft.com/kb/306126

Alternatively, you could use a router (register the router's MAC address with IT services). Steer clear of routers with built-in ADSL modems - they don't have the RJ45 WAN port you need.

bricks

Then give him the MAC address of the router.
You can then plug in as many devices as you wont behind your router.

Playboy

ok thx a lot guys!