FritzBox loses LAN connection, maybe? IDK, this is weird.

[ZeroKey]

This is a weird one, I can't even figure out where to start in figuring this out.

 

Hello everybody!

I recently started having issues with my network, specifically my LAN connected devices.

 

My network is set up the following way:

Outside fiber -> Telekom fiber modem -> FritzBox 7590 (router) -> ca. 10m (~33ft) CAT5e LAN cable -> TP-Link TL-SG105 -> 2 PCs and a wired WLAN-AP.

 

 

Tl;dr (for details, read the rest): I randomly lose LAN connection to my router. I can sometimes get it back. When I get it back, I sometimes still can't reach the router or the internet. Surefire way to fix it is rebooting the router. Have no clue what is going on.

 

 

I should mention, the cases I'm describing here are not all one event but multiple events where sometimes one of the solutions I tried worked BUT there was one event where I did everything in the described order.

Here it gets weird: When I walk out of my room I directly walk past the switch. It's on the bottom of a shelf with the LAN cable running underneath the shelf. When I come back to my PC, I've lost LAN connection. Further, the line coming in on the switch shows up as disconnected.

So, my first thought was, maybe the cable and the super janky LSA connector I use to connect the end of the cable coming out of the wall to another cable that then goes into the switch slightly moves when I walk past it (this building is about 90 years old) and there is a bad connection. So, I pulled it apart, confirmed it works fine with a multi meter and put it back together. Issue persists. It's also not guaranteed to fail when I walk past it. Instead, it fails randomly.

Next thing I did was log into the FritzBox with my phone to see what it can tell me. LAN shows up as disconnected. I go and just change all the ports. Go from port 0 on the FritzBox to port 1 and shuffle all ports on the switch. LAN shows up as connected on the FritzBox again but no devices. Weird... I check my PC and it tells me, no internet access but LAN is connected. Even weirder... I'm pretty much at a loss and start throwing stuff at the wall to see what sticks. /ipconfig renew is the first thing I think of, and it tells me the DHCP-Server isn't replying. But I can see that something assigned an IP to my PC. I change the port speed on the FritzBox from 1Gbit to 100Mbit and boom, my PC shows up as connected to the FritzBox, but I still don't have internet AND I can’t reach the FritzBox from my PC. So, renew again, I think. Still no reply from the DHCP-Server. What?! Switch the port back to 1Gbit and nothing changes. PC still shows up, still can't reach the FritzBox or reach the DHCP server. Only thing left that I could think of, is reboot the FritzBox and now everything works fine. A few hours later (I've walked in and out of my room multiple times now) I walk out of my room and come back: LAN connected but no internet access. Huh? Try to reach the FritzBox with my PC, nope. Log in with my phone, LAN connected but no devices. I just, what?

 

I know enough about networking to know that I know nearly nothing and not enough to even begin figuring this out. I know a thing or two about wires, wiring and how important shielding is to know that the LSA connector is jank but works fine and isn't affected by the floor subtly shifting when I walk past it. If pulling on the cable (dw, I'm not yanking on it) to get it out underneath the shelf doesn't affect it then why would walking past it? Beyond that I have absolutely no clue what is going on.

 

I did run the cable my self and there are no points where someone could walk over it or even damage it in any way. What I'm saying is, it's done right.

 

Any help in diagnosing the issue or even fixing it would be much appreciated.

 

English isn't my first language if there are any points where something isn't clear, I apologize and please don't hesitate to ask for clarification.

 

Thanks in advance,

Zero

Edited July 24, 2023 by ZeroKey
Added tl;dr

[Senzelian]

First things first: You need to get rid of all the unnecessary information in your op. Way too much text.

 

So from what I understand, the issue comes from the ethernet cable that's connecting your switch and router. You said you tested this cable with a multimeter and that it's somehow held together via some sort of LSA+ "connector". How exactly have you tested the connection and what sort of "connector" are you referring to? Is it a keystone? Is it a network socket?

(btw. don't call it a FritzBox. It's a router. This is an international forum, people don't know what a FritzBox is)

[ZeroKey]

6 minutes ago, Senzelian said:

First things first: You need to get rid of all the unnecessary information in your op. Way too much text.

 

So from what I understand, the issue comes from the ethernet cable that's connecting your switch and router. You said you tested this cable with a multimeter and that it's somehow held together via some sort of LSA+ "connector". How exactly have you tested the connection and what sort of "connector" are you referring to? Is it a keystone? Is it a network socket?

(btw. don't call it a FritzBox. It's a router. This is an international forum, people don't know what a FritzBox is)

It's a two minute read and I included every piece of info that I have so people don't have to ask for more info.

 

The issue is, that I lose LAN connection to my router but I also don't. I sometimes lose LAN connection for some reason but when I get it back I can't reach the router or the internet. The router however is still connected to the internet and WLAN works fine. Rebooting the router fixes the issue.

 

The LSA connector looks like this (not exact same model). I don't know what the correct term for this thing is so, I called it a connector. Sorry for the lack of clarity on that sentence, I didn't check the cable with a multi meter I ohmed out the LSA thing, to see if any of the connections had high resistance and I checked for current leaks to see if maybe the connections where interfering with one another. As I said, I know a thing or two about wires and wiring, it's part of my job.

 

If I call it a router without offering any further description of what it is I WILL get questions about what router I'm using. Calling it by it's name, avoids that.

 

Either I'm reading way to much into this, or I really don't like your tone. Feels condescending.

[Senzelian]

15 minutes ago, ZeroKey said:

Either I'm reading way to much into this, or I really don't like your tone. Feels condescending.

I've been on this forum for a little while as you can see and history shows that OPs with large amounts of text and tech people don't recognize don't generate any views. That's why I'm saying it. I'm not trying to be an asshole, I'm just trying to get to the point. That people won't know which router you're talking about isn't an excuse. You can still mention the model name within the OP.

 

That LSA+ coupler is something you should get rid of. No matter if it's causing an issue or not. Either get the appropriate cable for the job or terminate the cable with RJ45 jacks and connect them together with a RJ45 coupler like this one: 

 

Spoiler

 

I'm not sure what's causing you to not be able to restore the ethernet connection after the link loss, but I feel like it's a separate issue. If you don't experience the link loss in the first place, it wouldn't be an issue, so I'd ignore that for now.

 

For properly testing ethernet connections I highly recommend getting a good quality ethernet cable tester. They're cheap and can spare you a headache. 

 

Edit: Also do experience similar issues with any other LAN-connected devices? What else is connected to the switch?

[ZeroKey]

2 minutes ago, Senzelian said:

I've been on this forum for a little while as you can see and history shows that OPs with large amounts of text and tech people don't recognize don't generate any views. That's why I'm saying it. I'm not trying to be an asshole, I'm just trying to get to the point.

 

That LSA+ coupler is something you should get rid of. No matter if it's causing an issue or not. Either get the appropriate cable for the job or terminate the cable with RJ45 jacks and connect them together with a RJ45 coupler like this one: 

 

  Reveal hidden contents

 

I'm not sure what's causing you to not be able to restore the ethernet connection after the link loss, but I feel like it's a separate issue. If you don't experience the link loss in the first place, it wouldn't be an issue, so I'd ignore that for now.

 

For properly testing ethernet connections I highly recommend getting a good quality ethernet cable tester. They're cheap and can spare you a headache. 

I see, I will put a tl;dr ahead of the text so people can get a quick glimpse of the issue and if they need more info they can read the rest.

 

Yeah, the coupler is shit, I know. I will fix that. I've been uneasy about it from the moment I bought it but I was lazy.

 

Good idea on the cable tester. I'll look into that.

[Senzelian]

3 minutes ago, ZeroKey said:

I see, I will put a tl;dr ahead of the text so people can get a quick glimpse of the issue and if they need more info they can read the rest.

 

Yeah, the coupler is shit, I know. I will fix that. I've been uneasy about it from the moment I bought it but I was lazy.

 

Good idea on the cable tester. I'll look into that.

pm or quote me if you require further help. I'm in Germany as well and know these damn AVM ShitBoxes all too well, (they're actually pretty good most of the time) but before we get out the big guns, try shooting for the easy to fix things.

[ZeroKey]

22 hours ago, Senzelian said:

pm or quote me if you require further help. I'm in Germany as well and know these damn AVM ShitBoxes all too well, (they're actually pretty good most of the time) but before we get out the big guns, try shooting for the easy to fix things.

Got one of those cheapo chinesium network cable kits. Included plugs but not cable boots for some reason. Still... 17€, I'm not complaining.

Had a short on one of the lines. Got rid of the crappy coupler and properly terminated the cable, albeit with a cable boot made out of electrical tape.  Will observe if the issue comes back.

Thanks for your help! Let's hope this fixed everything.