I recently moved into a room in a dormitory. This room has a wired internet connection.

The problem is that when I plug the cable into my laptop (HP Pavilion g15) it doesn't detect anything, it is like there is no cable and I tried everything from changing the cable to trying my laptop in another room.

It is actually a problem in the whole building, some students can connect, others can't. My friend's laptop can connect to the network using my room's connection.

My question is : Can the ISP block a connection so that the laptop can't even detect the network ?

UPDATE : -When I said "like there is no cable", I meant literally, windows doesn't detect that there is an ethernet cable connected.

-I tried all possible scenarios (changing the cable, connecting my laptop in a different room,etc) but nothing worked, it seems that the network allows some laptop to connect from any room and denies other laptops access also from all rooms. I also made sure that my ethernet port is working by connecting it to a router.

-There is no registration process to get access, you just insert the cable.

-I had already notified the housing office with the issue and they contacted the ISP, they have been trying to solve the issue for 3 weeks now and I really don't know why it is that difficult for them.

UPDATE : It has been a year and I almost forgot about this question but here is what happened next in case someone is interested :

The issue persisted for about a month, some laptops were able to access the network from all rooms (i.e. wall plugs), other laptops can't even detect it also from all rooms.

I contacted the people in charge in the dorms but they were extraordinarily slow so I had to do something on my own. I bought a small Wifi repeater, plugged the Ethernet cable into it and it worked right away with no extra config.

After a week or two some IT guys came to the building and installed routers in all the rooms (even for those who had no problem connecting). These were regular routers and they installed it just as I installed the repeater (which I took back to the store).

No one knew what was the original problem. I think they even decided to install the routers because they didn't know what was wrong. The single most strangest internet problem that happened to me.

  • 12
    The ISP won't (And probably can't), be blocking anything that leads some computers to have the internet and some not.
    – barlop
    Commented Mar 18, 2018 at 23:41
  • 1
    You might be able to do some more troubleshooting about which laptops can connect and from which connection points. You could also experiment with long cat5 cables
    – barlop
    Commented Mar 18, 2018 at 23:42
  • 2
    Does your friend use the same cable in the same position in the same wall plug, and they have internet access while you don't? Does your friend's computer have a static address, or gets one through DHCP right away? Does your laptop work with the same cable connected to something, else like a router? Try plugging a router into the lan cable and see if it has access/gets an address, then to your computer (wired or wirelessly)?
    – Xen2050
    Commented Mar 19, 2018 at 1:30
  • 7
    @barlop an ISP (his campus absolutely can block some computers from accessing the internet and/or LAN
    – Keltari
    Commented Mar 19, 2018 at 5:28
  • 2
    @Keltari You wrote " an ISP (his campus absolutely can block " <-- An ISP is different from the campus / team that runs the university's router(s).
    – barlop
    Commented Mar 19, 2018 at 5:37

7 Answers 7


First, yes, your ISP can block your computer. Can they do it permanently and perfectly? ... probably not, but they can make it hard enough that you don't bother doing it and find another solution.

That's not the real question though. The real question is: "Did your ISP block your connection to their network?" I suspect, unless they believe they have a reason to, that they did not. This suspicion comes from the fact that you're in a dorm, which implies a school, which implies a liberal approach to information access.

I strongly suggest relaying your issue to the folks in charge of supporting the network connections for your dorm or your school (helpdesk, tech support, IT, network ops, etc.). They may have a registration requirement before you connect that you haven't finished going through, or perhaps your roommate by connecting first became the "registered" user, and you need to make an explicit request for your computer to be added / registered / permitted.

If they believe they have a reason not to permit you access, you will learn that most quickly by contacting them.

  • 32
    Sounds like MAC address filtering
    – Keltari
    Commented Mar 19, 2018 at 5:27
  • 8
    It could be, or it could be 802.1x as mentioned in another answer, or it could be a mis-configuration / configuration choice as mentioned in a comment to another answer, or it could be that the laptop is not participating in Network Access Control, or not able to view a web page with instructions on connecting or many things. Commented Mar 19, 2018 at 5:35
  • 3
    +1 for contacting School IT support, they will, should know better than anyone what is going on and how to proceed to help connect. Also it is possible that you have to connect and then go to a webpage and accept a set of terms and agreements?
    – Robby1212
    Commented Mar 19, 2018 at 12:51
  • Many colleges have special conditions to allow you to connect to the network. Usually, the moment you attempt to use the internet the network redirects you to an intranet page prompting you to "scan" your computer and download things to ensure your computer is virus free, as well as making you agree to some terms and conditions. Think of when you go to use public internet, you almost always have to agree to something. Sometimes this page doesn't come up automatically, leaving you stuck with no internet access. The IT department on campus should be able to help you with this.
    – Mohgeroth
    Commented Mar 19, 2018 at 14:46
  • 2
    This is not quite consistent with "like no cable"; I can detect the difference between MAC filtering and an unplugged cable with 100% reliability.
    – Joshua
    Commented Mar 19, 2018 at 20:50

This doesn't sound like an ISP issue, it sounds like the dormitory may have implemented 802.1X authentication on their Ethernet. If so, your laptop needs to have the proper profile installed so that it can connect to the LAN.

We used this mechanism at a company I worked for, so that visitors couldn't connect their laptops to our internal network (I think there was a separate "public" LAN that they could use to access the Internet).

  • 1
    I thought 802.1x at first, too, but if that were the case Windows would still detect something on the network line. 802.1x allows enough traffic to complete authentication. Commented Mar 19, 2018 at 21:43
  • @JoelCoehoorn I can't think of anything that could make it seem like there's no cable at all -- if there's any kind of filtering or blocking, it needs to be able to communicate enough for the switch to decide whether to block it.
    – Barmar
    Commented Mar 19, 2018 at 22:16
  • When I was in college 15 years ago, we had to sign up to have the port activated. They actually physically plugged in a patch cable for each room (I know this because I worked for ResNet one year). It was a different era :), but I wonder today if they might need to set the port to administratively enabled. I can't think what would make it work for the friend's laptop to work. Even MAC filtering would show the basic link up in Windows :( Maybe a failing power supply on the switch. Commented Mar 19, 2018 at 22:26
  • Wait... I got it! STP could do this! If someone bridges their wifi connection to their LAN port, connects to the institution wifi, and then plugs into the LAN port, STP will kill the port dead. Commented Mar 19, 2018 at 22:29
  • So the port would be live momentarily, but dead by the time he looks at it. Would the network admins have to re-enable the port manually to undo it?
    – Barmar
    Commented Mar 19, 2018 at 22:50

Talk to the people who run the network (presumably, your campus IT department's helpdesk).

It's quite common for networks to be set up so that only authorized machines can connect. For example, at my workplace, each network port has a list of computers that are allowed to connect to it. By default, that list is "none at all"; my desktop computer has its own dedicated port that no other computer can use, and my laptop also has its own port (though I mainly use the wifi for that). This is done by storing the MAC address of the machine – the hardware analogue of a phone number that's used to transfer data to that specific machine.

It would be unsurprising if your campus network has such a policy. University resources are provided only to members of the university and, more specifically to people who have agreed to the network's acceptable use policy. They will also want to protect the network from people doing dumb things like attaching an open wifi router to it, allowing anybody out on the street to access the internet through the university's connection.


A campus network is not an ISP by every definition - they are providing internet service, but not in the same for-profit, individually billed manner as ISPs commonly do.

Whereas ISPs commonly use some kind of account credentials to grant or deny access to the router (or directly connected computer) at a customer's home, campus networks (and some old school cable networks) commonly use an authorization scheme based on the so called MAC address that is unique to every Ethernet network card (or network port built into a computer's main board). You will need to talk to whoever runs that campus network for instructions on how to get the address of your computer(s) authorized.

Alternatively, there might be 802.11x authentication in use on that network - again, the responsible staff should be able to tell you.

By the way, only plug network cables into jacks where you are SURE they are intended as Ethernet connectors, and for YOU to use. A random RJ45 outlet in a building could just as well be ISDN, or a network you have no business using, or entirely something else. Also, while you CAN change the MAC address of your computer in some cases, DO NOT do that. The trouble and confusion you can cause to network maintainers that way will not make them your friends.


This would not be an ISP level issue - it sounds like an issue with the switches on the other side of those wall jacks - Maybe an issue with port speed/duplex negotiation, or an issue with STP configuration.

  • 3
    heh, If I recall my CCNA classes correctly they could have set up sticky switchports and forgot. If a switchport has never been used before it'll stick to one port, and if its set to be sticky and the mac addresses are not saved to NVRAM... and they reboot....
    – Journeyman Geek
    Commented Mar 19, 2018 at 3:17

Did your try with both straight through and crossover cables?

Nowadays, I would expect every network card to support automatic crossover, but if it didn't, it could lead to the reported behaviour if you were using a crossover cable (or fail only when using a straight through cable, if the wrong cable/setting was used when patching the room).

Computers that are using a network card with automatic crossover would work on the same socket with the same cable, and the 'failing' machine could work on a different socket where the wiring was done differently, or it is connected to a switch supporting automatic crossover.

  • Rather than trying random things, it makes much more sense to just ask the college's IT support people. Commented Mar 20, 2018 at 20:22

Have you confirmed that your laptop ethernet connection works on any other network when you plug in with a wired connection?

Sounds like you've already tested with a known good on the problem connection in your room and it's working?

Do you have a manual IP address assigned to your physical network adapter?

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