Hi all,
I am not a network expert. I'll try my best to express my situation to the best of what i have grasped and after discussing with some network administrators. I think it is just an intention issue that they are not allowing my system to connect.

so this is a school where i work. i am a teacher. there are about 100 pcs . I am the only one that have installed Linux in my school pc. (Thankfully they did not object) . For the last 6 years i had no issue connecting to the network and using internet for our regular school work. They even have a firewall setup . So when i open firefox , a firewall page opens . i am just supposed to enter my userid and password and my internet works. This is all happening through lan connection. ( i can anytime choose to use the wifi as well) recently we shifted to a new building. our pcs were transported to this new building. they did a fresh network install in the entire place. August month we started. During August month for 15 days my Lan worked just like before. its the same Linux pc i use and same os. Everyone else are as usual windows. Then i noticed intermittently the Lan would not connect in my pc. noticed few others were having similar issues. i ignored it thinking teething issue as we are in a new building and network is still getting fine tuned. but as days went it is just my Linux pc not connecting to Lan. i tried reconnecting physically no effect. pulled my lan wire and connected to my collegues windows pc it works there . pulled his lan cable and connected to my linux pc and still not connecting. i thought something broke in my os . Reinstalled. updated kernel. still same issue. ran live iso. still same trouble lan would not connect. wifi would connect everytime and i could use net. but the wifi is weak and keeps disconnecting. by this time i understood the problem is not my pc but something is wrong at the server side. i contacted my admin. he tried to hide the issue under the rug by bringing a windows laptop and showing that the net is working using my lan .so he concluded my linux pc is the issue. Either he is a novice or pretending . luckily i found two outsourced guys who were visiting for network repairs in my school. i described the issue to them . they said some policies or rules have been set in the server. that is why my linux is not connecting. Normally it shouldn't happen. Linux follows generic rules. So it should connect but server side is doing something . I told him why wifi connects well. He said wifi will connect always. Lan will give an issue. he said the only solution is to use static IP. So what he did was connected my pc to wifi . copied the mac id and some ip details from my terminal and sent to the admin. Now they have to do something there to allow my pc to connect. its been 2 weeks this has not happened. Please tell me is this all true . is there more details that i may not be aware of. I need to complain to my school head and explain the situation clearly. what exactly should i tell him so he understands. i tried setting my pc to static . pasted new ip that i got from wifi connection. The lan managed to connect but now i don't get the firewall page. nothing opens. So static ip got me closer to my goal. I am guessing they need to set something from their end. please guide.

Hi
Nothing new there, happens all the time.
Organisations have policies, SLAs, support models, etc to adhere by and a fleet of 100 devices would be considered a very small environment.
If your students bring byod laptops/devices... then yours would be considered same and should be supported.

Lets begin with what Linux flavour you are running and also year/make/model of your laptop.
Then reboot your laptop, connect to the wired only and as 'root' copy/paste the dmesg command into a text file and upload it here.

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The firewall page seems to be more of a WIFI captive portal. It is used to "log" the connection to the user more than anything, much like a hotel does.

So there are various methods for Lan Security. The admins copying a MACid might be port security, which allows only that MACid to talk
to that port. Lets assume they did this (often a port will go down if it detects the wrong mac on it, but some just won't allow it to work.)

The network on the LAN might not be the same as the one on WIFI, it often isn't. What I usually do is tcpdump/wireshark the interface on your Linux box. Often you can see router advertisements to figure out what actual network is there or broadcast messages. It might be the same network as wifi but your static won't work unless you figure this out.

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Thanks that is reassuring

Forgot to mention. Initally i even thought that my lan port is damaged. So i tested a usb lan socket dongle. i had one. But that too showed same behaviour. All of these confirmed me that issue has to be server side.

Also that firewall page is a fortinet captive portal as rightfully pointed out by another expert.
This is a
Hp Desktop AIO 120 2110 il
Year is probably around 2013
link for product image and description
http://www.bsocialshine.com/2014/09/...e-desktop.html
https://www.flipkart.com/hp-omni-120...m24be4e3e4bb89

You may think this is a very old PC. it is . but with linux everything works at good speed.

Linux Mint 20.2
kernel 5.15.0-33
processor 64 bit Intel G630 2.7GHz x 2
Ram 4 GB
Network controller: Ralink corp. RT5390 Wireless 802.11n 1T/1R PCIe
Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit

root dmesg output saved in text file

Attached Files

dmesg output.txt (54.2 KB, 17 views)

I did tcpdump. There was a continuous flow of output. i did ctrl c . Do you want to me save the output to text file and upload here? .
The last 3 lines of the output was this .
154 packets captured
154 packets received by filter
0 packets dropped by kernel

Had a look at the file you provided.
Saw Netlabel and wondered what was that doing in there... but it should not be impacting.
Then I saw 'systemd' in there, apologies but not going to troubleshoot that trainwreck.

Your local NIC appears good though it is showing down
[ 25.188537] RTL8211DN Gigabit Ethernet r8169-0-300:00: attached PHY driver (mii_bushy_addr=r8169-0-300:00, irq=MAC)
[ 25.469338] r8169 0000:03:00.0 enp3s0: Link is Down.

I would download a 'live' iso of either Devuan or Slackware iso, burn it to a usb stick and boot from it.
If the issue still occurs while testing from a non-systemd flavour of Linux, then it is likely not your laptop.

May the force be with you.

Link down, not good.

I am wondering if tcpdump worked right.

Make sure when you tcpdump, you get the right device, tcpdump -v -i enp3sO. tcpdump tells you the device on the first line.

If the link is down, I suspect port security.

i have done that . uploaded the textfile.

Attached Files

tcpdump output.txt (9.3 KB, 4 views)

Devuan showed same behaviour. Was searching for network . uploading screen shot.

Attached Thumbnails

 

What was the network for WIFI and settings? IP and netmask or broadcast, default route.

I think I see 2 networks on the wire, 10.23.24.0 and 10.23.4.0.

Guys it got fixed. There was some cable issue at the network side someplace elsewhere. today a tech support found that problem. the moment he fixed that cable. here in my floor in my linux mint pc the lan instantly started. recently my windows users were experiencing network drops. so the problem was bigger and had to be checked thoroughly . it finally got fixed. there was no issue at my end at all.

Guys it got fixed. There was some cable issue at the network side someplace elsewhere. today a tech support found that problem. the moment he fixed that cable. here in my floor in my linux mint pc the lan instantly started. recently my windows users were experiencing network drops. so the problem was bigger and had to be checked thoroughly . it finally got fixed. there was no issue at my end at all.