Question DNS not working properly ?

[Celauron]

I've encountered an issue which I can't understand or solve myself, and been scouring forums for a month now - intermittently my pc or any devices connected to a router would lose connection to the internet. When this happens if I click on the Ethernet button in Windows and check its status "it says IPv4 connectivity: no internet available". Then I could either switch it off and on, or use troubleshooter, which does exactly the same thing and results in "The default gateway is not available" error. Meanwhile - router itself works, wi-fi works, and I even accessed it from my phone to check it multiple times. Similarly - sometimes wi-fi connection on my phone stops working and displays "err_name_not_resolved", while internet connection on pc is working perfectly fine.

If I connect to VPN or manually enter google or any other public DNS either in router settings or phone - internet connection starts working again. Which points to DNS issues on the router.

My Ethernet Adapter is I219-V built in Asus motherboard, and my router is Asus rt AC68U

I don't have any specific settings or changed anything on the router page, and even removed some open ports I needed to check if the issue remains. I have tried reinstalling drivers, changing various settings, assigning default ip directly into tcp/ipv4 (resulted in no internet at all for some reason) but nothing has worked so far. The only thing I ever did to my router is updating its firmware and rarely opening specific ports, I did not change any other settings for years.

 

[bill001g]

If you think it is the DNS you can manually set it in the IPv4 settings. I would set it to 1.1.1.1 or 8.8.8.8 I would disable the ipv6 while you are in the setting screens.

Note DNS can now be overridden in many browsers. This can be a good thing since it supports encrypted DNS but it can be confusing if the DNS server used in the browser is different than the system dns and there is a problem with a DNS server.

The problem is if your internet goes down it will tell you it has DNS issues....well duhh can't get to any servers including the DNS servers. So a message saying there is a DNS problem may not be a actual DNS issue.

The best test is to leave a constant ping run to 1.1.1.1 in a background window. If the internet goes down you will see packet loss on this.

I guess it depends on how long these outages are. If they are longer can you get into the router and try a ping test from there. The asus routers have the ability to run ping commands from the router itself. You can use both name and/or numeric values so it can test dns server issue in addition to simple network connectivity.

There also should be a system log, it might give you a indication if the internet is going down.

 

[Celauron]

If you think it is the DNS you can manually set it in the IPv4 settings. I would set it to 1.1.1.1 or 8.8.8.8 I would disable the ipv6 while you are in the setting screens.

Note DNS can now be overridden in many browsers. This can be a good thing since it supports encrypted DNS but it can be confusing if the DNS server used in the browser is different than the system dns and there is a problem with a DNS server.

The problem is if your internet goes down it will tell you it has DNS issues....well duhh can't get to any servers including the DNS servers. So a message saying there is a DNS problem may not be a actual DNS issue.

The best test is to leave a constant ping run to 1.1.1.1 in a background window. If the internet goes down you will see packet loss on this.

I guess it depends on how long these outages are. If they are longer can you get into the router and try a ping test from there. The asus routers have the ability to run ping commands from the router itself. You can use both name and/or numeric values so it can test dns server issue in addition to simple network connectivity.

There also should be a system log, it might give you a indication if the internet is going down.

I was using Google dns for about year without issues. I simply entered 8.8.8.8 and 8.8.4.4 in my router settings. However, - issues started WHILE I was using Google dns. I can't even call this an outage, since PC would simply lose internet connection until I restart the Ethernet adapter manually or through troubleshooter, at the same time wi-fi was working and connection was available on other devices. So the internet was working, but DNS or DHCP wasn't.

I have checked system logs multiple times - and they do not mention anything at all when the "outage" happens. The issue also seems to happen regardless of which DNS I am using - it happened with default (no specific dns selected and getting it from ISP) and google, quad, adguard. In fact - I thought that the whole reason for the issue is that ISP is somehow interfering with Google or other public DNS services, since all outages happen after 10PM, and usually no more than 1 or 2 times in a span of a few hours. After that - everything could be working fine for days. It didn't happen yesterday, for example, after I switched to ISP DNS... but that resulted in my phone no longer connecting to the internet without VPN or using mobile connection, and I had to manually enter Google dns services in my iphone settings for wi-fi to work. The fact that phone is unable to get DNS also points to router issues, I think?

I will try leaving ping window. Though I am not technically savvy to even understand what exactly it will accomplish. Found a ping tool in router settings as well.

 

[bill001g]

You want to set the DNS in your PC not in the router.

The default is to use your router as a proxy to in most cases the ISP dns. You changed the router dns to google rather than the ISP which fixes the issue with ISP crappy dns. The other thing that causes problems more than the ISP dns is the proxy.
What you need to do is set the DHCP server in the router to give your end device the actual dns server rather than its own address which is how the proxy is done. You can also manually set the dns in the end device.

 

[Celauron]

You want to set the DNS in your PC not in the router.

The default is to use your router as a proxy to in most cases the ISP dns. You changed the router dns to google rather than the ISP which fixes the issue with ISP crappy dns. The other thing that causes problems more than the ISP dns is the proxy.
What you need to do is set the DHCP server in the router to give your end device the actual dns server rather than its own address which is how the proxy is done. You can also manually set the dns in the end device.

I think I know how to set it on the PC directly - in ethernet adapter settings -> ipv4, and just enter 8.8.8.8, but you lost me on the second part. How do I configure DHCP server in the router?

https://imgur.com/a/etS2mo4

View: https://imgur.com/a/etS2mo4


This is how my DHCP page is looking at the moment. I did add my PC to DHCP list few days ago, though it didn't do anything and the issue still happened.

Also - what's the danger of setting DNS in my router? Asus seems to have a button for it and even gives you a list of popular DNS services, it also helps with the phone issue, since I don't have to enter DNS manually on the phone.

This is how WAN page looks at the moment

https://imgur.com/Bq5FXM4

View: https://imgur.com/Bq5FXM4

https://imgur.com/BZPWrpj

View: https://imgur.com/BZPWrpj

 

[bill001g]

It is pretty simple just put the the dns servers you want to use in the 1 and 2 fields in the first screen. I would turn off the option for the router to give its IP also.

If you look at IPCONFIG /all you will see a field called DNS server. The default is it will be set to the router IP. When you use this option in the router it will show the 2 different IP you specified.

I can see no downside to doing this and I always do it. It tends to be pretty much the only way to set the dns value in some devices like phones.

The value in the wan doesn't matter much since that is the DNS the router itself uses and what the router will proxy to if you do not specify the dns server. I don't understand what the proxy function is suppose to buy you. It can cache some results but dns is such low volume I can't see it speeding stuff up.

The reason I still set it manually in the IPv4 settings is to use the new options in windows to use encrypted DNS. I don't know if you can do this via dhcp. Then again the encrypted DNS is used mostly by browsers so you can let the DHCP assign it to the computer but use the browser settings to set the encryption options. It is only very recently that microsoft added this encrypted dns option. I know one of the machine I do not allow updates on does not have it.

 

[Celauron]

The value in the wan doesn't matter much since that is the DNS the router itself uses and what the router will proxy to if you do not specify the dns server. I don't understand what the proxy function is suppose to buy you. It can cache some results but dns is such low volume I can't see it speeding stuff up.

The reason I still set it manually in the IPv4 settings is to use the new options in windows to use encrypted DNS. I don't know if you can do this via dhcp. Then again the encrypted DNS is used mostly by browsers so you can let the DHCP assign it to the computer but use the browser settings to set the encryption options. It is only very recently that microsoft added this encrypted dns option. I know one of the machine I do not allow updates on does not have it.

I am still a bit confused - what is the difference between setting DNS servers in those two fields, and selecting it on the WAN page with the router button? Just now I put Google dns in those two fields, did ipconfig /all and now I see 8.8.8.8 and 8.8.4.4 in DNS field, so it seems to be working.

What about Ethernet adapter though?

https://imgur.com/QvpU3Mn

View: https://imgur.com/QvpU3Mn


Do I also need to put it in ipv4 settings, or not since I did it on the DHCP page? I honestly don't know anything about Windows encrypted DNS, not even sure I need it just for personal use.

After about 10 minutes since I set DNS to google servers - I got the same issue again, and lost internet connection. I was running ping and it simply timed out.

 

[bill001g]

The ones in the WAN is what ISP put in their DHCP server to give out to their customers.

The ones you put in the DHCP server on your router gives this out to devices on your lan.

The ones you put in the IPv4 setting override the ones you get via DHCP.

If you lost a ping to say 1.1.1.1 then the problem is your internet connection is going down. It is not actually a DNS problem. When you ping a numeric IP you are not using DNS.

You could leave a second ping run to your router IP at the same time as the 1.1.1.1 This will confirm the problem is not your router crashing or something strange and is on the internet.

The next step if you call the ISP and they still claim to see nothing is to run tracert 1.1.1.1. The goal here is to get the IP addresses in the path the command itself will not likely show any errors unless you are very lucky.

You want to now leave ping run to hop1 (should be your router IP) hop2- this should be the first ISP router and represent the connection between your house and the ISP. And finally run the ping to 1.1.1.1.

What you hope to see is no loss to hop 1 but you see loss to hop 2. This pretty much proves it is the ISP. If you give them the ping to 1.1.1.1 they will try to blame the server. Very random outages are somewhat hard for the ISP to find. What you might try is to download at 50% of what you pay for. You can set something like steam to only use a maximum bandwidth. The run the ping tests again. Generally traffic on the connection makes the problem worse. The reason to limit the speed is it is normal to get packet loss if you are using 100% of the bandwidth and is not a valid test.

 

[Celauron]

If you lost a ping to say 1.1.1.1 then the problem is your internet connection is going down. It is not actually a DNS problem. When you ping a numeric IP you are not using DNS.

That's just it - connection on my phone continued to work, so wi-fi was up and that means that it's not probably ISP. But I will try running ping on the router, or 3 like you suggested.

Question is - should I continue using google dns while doing this or not?

 

[bill001g]

Ok I though you said all your devices were losing connectivity.

If it is just 1 pc then it is more likely something with the pc rather than the router or internet.

I assume you mean you put 8.8.8.8 in when you say google dns. That is one of the best ones to use, I just use cloudflare 1.1.1.1 because they allowed encrypted dns before google and I never changed back.

So what you now want to do is leave a ping run to your router IP. Your goal here is to see if you are losing connectivity to the router ip. This will show if you are losing basic network connectivity or it is something more complex. It almost has to be this. Since you ping by IP address and get loss AND you know the internet is functional because other devices work that pretty much leaves the pc or the cable going to the router as the cause.

You might also see something interesting if you do IPCONFIG /all while it is broken. You are looking to see if it is in status disconnect which indicates a hardware issue, most likely the cable or the port is connected but there is something wrong with the IP addresses.

 

[Celauron]

Ok I though you said all your devices were losing connectivity.

If it is just 1 pc then it is more likely something with the pc rather than the router or internet.

I assume you mean you put 8.8.8.8 in when you say google dns. That is one of the best ones to use, I just use cloudflare 1.1.1.1 because they allowed encrypted dns before google and I never changed back.

So what you now want to do is leave a ping run to your router IP. Your goal here is to see if you are losing connectivity to the router ip. This will show if you are losing basic network connectivity or it is something more complex. It almost has to be this. Since you ping by IP address and get loss AND you know the internet is functional because other devices work that pretty much leaves the pc or the cable going to the router as the cause.

You might also see something interesting if you do IPCONFIG /all while it is broken. You are looking to see if it is in status disconnect which indicates a hardware issue, most likely the cable or the port is connected but there is something wrong with the IP addresses.

I actually did ipconfig /all while it was down and nothing was changed from when it was working. Yeah I am using 8.8.8.8 and 8.8.4.4

What doesn't make sense and I think is also related to the issue - is that everything works fine if I only enable VPN or use any custom DNS on either phone or pc. Previously I never had to use dns at all. Yesterday, DNS on router literally wouldn't assign an address to my phone so the internet didn't work until I selected google dns. Today, I disabled everything, set dns to receive from ISP and disabled vpn - and everything works fine both on the phone and on the pc.

Overall it feels like an issue with the router (I replaced cable earlier, just in case), specifically something to do with DNS or DHCP momentarily stopping working.

 

[Celauron]

So what you now want to do is leave a ping run to your router IP. Your goal here is to see if you are losing connectivity to the router ip. This will show if you are losing basic network connectivity or it is something more complex. It almost has to be this. Since you ping by IP address and get loss AND you know the internet is functional because other devices work that pretty much leaves the pc or the cable going to the router as the cause.

You might also see something interesting if you do IPCONFIG /all while it is broken. You are looking to see if it is in status disconnect which indicates a hardware issue, most likely the cable or the port is connected but there is something wrong with the IP addresses.

This is what I found in the log, while pc has lost connection today again:

Aug 13 19:35:09 dnsmasq-dhcp[28457]: DHCPREQUEST(br0) 192.168.1.125 xx:xx:xx:xx:xx:xx
Aug 13 19:35:09 dnsmasq-dhcp[28457]: DHCPACK(br0) 192.168.1.125 xx:xx:xx:xx:xx:xx User
Aug 13 19:35:09 dnsmasq-dhcp[28457]: DHCPREQUEST(br0) 192.168.1.125 xx:xx:xx:xx:xx:xx
Aug 13 19:35:09 dnsmasq-dhcp[28457]: DHCPACK(br0) 192.168.1.125 xx:xx:xx:xx:xx:xx User

Instead of xx:xx:xx:xx:xx:xx - there was a mac address of my PC. While this happened - I was using google dns 8.8.8.8 and 8.8.4.4 in the lan settings.

 

[bill001g]

This is getting into the area of using linux stuff to do DHCP which I have limited knowledge. Most routers are linux based.

I think if I remember correctly this function is to put the IP address of the machine into the DNS server on the router. This lets you use some name like PC1.localnetwork.com or whatever and it translates it to the address that can change as DHCP assigns different IP.
I don't know , everything where I used to work used microsoft domain server to do a very similar function as well as all the other group policy etc etc.

It is mostly a name more than anything else.

The DHCPREQUEST is a very common message it just means the pc either asked for a new IP or it asked to keep using its current one.

If you want to see the messages you can run wireshark on the pc and capture all the data. You can in very great detail see what is being send back and forth.

So maybe brute force this and put a fixed IPv4 IP in the pc, as well as fixed DNS. I am not sure what the range your router uses in the dhcp range. Technically you want to place fixed IP outside the dhcp pool. I would try 192.168.1.250 that one is high enough it seldom gets duplicated.

This will eliminate DHCP and DNS as the problem.

 

[Celauron]

This is getting into the area of using linux stuff to do DHCP which I have limited knowledge. Most routers are linux based.

I think if I remember correctly this function is to put the IP address of the machine into the DNS server on the router. This lets you use some name like PC1.localnetwork.com or whatever and it translates it to the address that can change as DHCP assigns different IP.
I don't know , everything where I used to work used microsoft domain server to do a very similar function as well as all the other group policy etc etc.

It is mostly a name more than anything else.

The DHCPREQUEST is a very common message it just means the pc either asked for a new IP or it asked to keep using its current one.

If you want to see the messages you can run wireshark on the pc and capture all the data. You can in very great detail see what is being send back and forth.

So maybe brute force this and put a fixed IPv4 IP in the pc, as well as fixed DNS. I am not sure what the range your router uses in the dhcp range. Technically you want to place fixed IP outside the dhcp pool. I would try 192.168.1.250 that one is high enough it seldom gets duplicated.

This will eliminate DHCP and DNS as the problem.

Today I was running pings to ISP and router, and when it happened - apparently I lost connection to router as well. So I assume that PC requests or renews lease and doesn't receive a response from router. I've changed the address to .250, also forced it to use google dns everywhere I could, will see what happens next. Router reset is next. I had no issues for 3 days before that.

 

[bill001g]

Pretty much the only way you do not get a ping back from the router IP when you have set the IP manually is if the router crashes. Even if the internet goes down the router will respond to the ping.

 

[Celauron]

Pretty much the only way you do not get a ping back from the router IP when you have set the IP manually is if the router crashes. Even if the internet goes down the router will respond to the ping.

Unless it's some weird issue which happens momentarily and fixes itself on the router, but not on the pc - I am not sure. Lost connection again today, reset router to default settings, and 20 minutes later lost connection again. Running wireshark now, but I can bet I am not getting more disconnects today. I even cleaned every connection and cable just in case beforehand.

 

[Ralston18]

Interesting thread:

@Celauron

Can you see the router from where you are working?

When connections are lost do any of the router's LED's change?

I am wondering if the router is experiencing power losses....

Maybe a loose power connection, faulty outlet/circuit, or some failing component in the router.

Something to look at just as a matter of elimination.

 

[bill001g]

You can tell if it is the router or something else if you have another device preferably also ethernet attached.

You should be able to ping this other device many times even if the router is hung. The lan ports on a router act as a simple switch. Even though it is on the same physical silicon as the router processor the lan ports act as if this was a separate switch chip.
Of course it depends on how broken the router is. If you have a real switch you could put in front of the router that would make the test more valid.

This is mostly to try to eliminate the pc or cable.

But as indicated above you generally will see the lights change on the router if it would reboot for example. maybe the log in the router says something interesting.

 

[ex_bubblehead]

This behavior is not uncommon at all for an almost 10 year old router. I've had to replace several of this model for clients over the past couple of years due to such failures. Rebooting the router returns everything to normal, for a while. My theory is that since they're powered up all the time that the heat has a cumulative effect that culminates in what you are seeing.

 

[Celauron]

Sorry for not answering earlier - since my last post, I've experienced one outage, which might have been related to VPN (not sure). I was waiting for more issues, but so far nothing is happening.

You should be able to ping this other device many times even if the router is hung. The lan ports on a router act as a simple switch. Even though it is on the same physical silicon as the router processor the lan ports act as if this was a separate switch chip.
Of course it depends on how broken the router is. If you have a real switch you could put in front of the router that would make the test more valid.

The router appears to be working fine, since while one device loses the connection - everything else is working fine and the router page is accessible from other devices. I did replace cables, but I can't check connections inside walls or to the ISP hardware. I was running pings to router and when the disconnect happens - pings fail. I used to have CCTV cameras connected via cable, but right now I just don't have any other ethernet cable running anywhere else to test it. If there's an issue with hardware - I would assume it would be cables running to ISP hardware, which was frequently disturbed by workers recently, but that wouldn't explain how the PC or router keep having issues with DNS/DHCP randomly.

Interesting thread:

@Celauron

Can you see the router from where you are working?

When connections are lost do any of the router's LED's change?

I am wondering if the router is experiencing power losses....

Maybe a loose power connection, faulty outlet/circuit, or some failing component in the router.

Something to look at just as a matter of elimination.

I've explained in the first post, but I do not think that router stops working at all - rather, the PC loses connection and gets "The default gateway is not available ", so both internet AND router page become inaccessible. It happens momentarily and while PC doesn't have internet - router itself continues working and other devices, such as phones, smart tv, tablet all still have connection to router (according to it's page which I access through phone while it happens).

Then, I would just restart the Ethernet adapter in Windows (not even restarting the router) and PC gets its connection back.

I would assume that if router would actually go down and then back up - it would lose connection to all other devices and actually take a minute to restart - this never happens, even the logs appear to be clean and working normally.

I've also experienced my phone similarly not having internet connection and unable to open router page, while internet on PC was working fine and router page was showing that everything is working.

Right now, I am starting to think that the issue is related to my ISP, perhaps blocking popular DNS services. When the issue first occurred I was using Google DNS, then I would switch it off, try other DNS, still get issues. Right now I am using DNS provided by ISP. I've also reset my router to factory settings, but the only setting which seems to be different from what I was using is UPNP and secure UPNP being enabled, which seems to be unrelated.

This behavior is not uncommon at all for an almost 10 year old router. I've had to replace several of this model for clients over the past couple of years due to such failures. Rebooting the router returns everything to normal, for a while. My theory is that since they're powered up all the time that the heat has a cumulative effect that culminates in what you are seeing.

It would seem reasonable, if only router ever actually stopped working, or needed to be rebooted. It never loses connection to all the devices, and never reboots. I've also been checking the temperature, rechecked and dusted all connections, and everything seems fine. Though eventually I will replace it if everything else fails.

 

[bill001g]

This is a rather old thread and I forget what has been recommended so I apologize if I repeat myself, I put very similar things into many thread and forget which.

The best solution if you think the ISP or any other device is messing with the DNS is to use encrypted dns.
I think you can now use either 8.8.8.8 or 1.1.1.1 but I tend to use cloudflare 1.1.1.1.

I would first try it in the setting in the web browser. Most web browsers now support this.

Depending on the patch level windows now also supports this. There should be a option to use encrypted DNS in the IPv4 settings.

But this is a far different issue than "default gateway not available". The default gateway is a IP address set by the router/dhcp server. It does not use DNS. It would never work if it used DNS because it needs to send traffic to a external DNS server BUT that traffic must first pass through the default gateway to get there. So you must always know the gateway IP before you use DNS...or really pretty much anything.

I would start to suspect the router has issues. Maybe try a firmware update if there is one. Since it affect multiple devices it is not likely the end devices. The other possibility would be if you have a conflict for the router/gateway ip. Maybe you have some other device...like a second router..using the same IP. arp -a might give you a clue. The mac address you see for the gateway IP should be the same as your router, and it should not change. If you have teen hackers in your house there ARP poison attacks that can cause this but it can only be done from a device already on your network it can not be done from someone external.

 

[Celauron]

This is a rather old thread and I forget what has been recommended so I apologize if I repeat myself, I put very similar things into many thread and forget which.

The best solution if you think the ISP or any other device is messing with the DNS is to use encrypted dns.
I think you can now use either 8.8.8.8 or 1.1.1.1 but I tend to use cloudflare 1.1.1.1.

I would first try it in the setting in the web browser. Most web browsers now support this.

Depending on the patch level windows now also supports this. There should be a option to use encrypted DNS in the IPv4 settings.

But this is a far different issue than "default gateway not available". The default gateway is a IP address set by the router/dhcp server. It does not use DNS. It would never work if it used DNS because it needs to send traffic to a external DNS server BUT that traffic must first pass through the default gateway to get there. So you must always know the gateway IP before you use DNS...or really pretty much anything.

I would start to suspect the router has issues. Maybe try a firmware update if there is one. Since it affect multiple devices it is not likely the end devices. The other possibility would be if you have a conflict for the router/gateway ip. Maybe you have some other device...like a second router..using the same IP. arp -a might give you a clue. The mac address you see for the gateway IP should be the same as your router, and it should not change. If you have teen hackers in your house there ARP poison attacks that can cause this but it can only be done from a device already on your network it can not be done from someone external.

I was using 8.8.8.8 and 8.8.4.4 (also something called quad9 which claimed to be extra protected) when the issues started happening, first inside router settings, then inside windows settings. I'll try browser settings now.

I still didn't get any issues so far after switching to ISP DNS, and I did update router when the issues began. Also reset it few days ago. Mac address seems to be correct as well.

I can see wi-fi devices connected to my network, 2 phones, 2 tv's, one table, one pc. All of them check out - those are my devices. But I did think that it almost looks like some "attack" which temporarily cause a device to lose connection with a router or something, but it sounds paranoid. I live in an apartment building, there are kids here, but I doubt they got nothing better to do than try to hack my pc.

Not entirely sure what ARP is.

 

[bill001g]

If someone want to just harass you it is possible to spoof a message that causes all your devices to disconnect. It is pretty pointless because the end device just reconnect in most cases and it does not compromise any security. Not very likely because it is a lot of effort to do this.
Would be simpler to just jam every ones wifi by just using their own wifi on the same channels and then constantly coping data....then again you have lots of people that do that and they are not even attempting to do anything bad.

Wifi disconnects are just one of those things you have to accept when you use wifi. It is generally caused by interference which is massive when you live near lots of other people.

If you have issues with a ethernet connection disconnecting and you are sure it is not the pc or the cable all that is left is some issue with the router.

 

[Celauron]

If someone want to just harass you it is possible to spoof a message that causes all your devices to disconnect. It is pretty pointless because the end device just reconnect in most cases and it does not compromise any security. Not very likely because it is a lot of effort to do this.
Would be simpler to just jam every ones wifi by just using their own wifi on the same channels and then constantly coping data....then again you have lots of people that do that and they are not even attempting to do anything bad.

Wifi disconnects are just one of those things you have to accept when you use wifi. It is generally caused by interference which is massive when you live near lots of other people.

If you have issues with a ethernet connection disconnecting and you are sure it is not the pc or the cable all that is left is some issue with the router.

To be honest, I am at a loss here - been two days since I switched to quad9 DNS, I changed settings inside browser, inside router, inside windows. Yet everything seems to be fine. Some sites are claiming that my ISP does in fact block ALL of those popular DNS services, but whenever I ping them - everything is working fine. And pc or the phone hasn't lost connection yet. I guess that leaves some peculiar router issue, perhaps slowly dying, memory not working correctly or maybe cache issues.

PC uses ethernet connection, not sure how someone would harass me and force disconnects from the router. Also, I have firewall/antivirus, and the router has its own firewall, and I am using VPN, and was using DNS. Hard to imagine how I could've protected my PC more, unless I'd put it inside a condom. So it probably wasn't someone harassing me after all.

 

[Celauron]

Just in case someone ever has a similar issue - I was able to fix it by using an old external ethernet card, instead of buit-in ethernet port. The motherboard is actually relatively new (few months) but Asus quality has been going downhill, so not very surprising. Separately, I have also found an issue with Avast antivirus - it's core web shield was occasionally blocking ALL internet access and confusing the diagnostic of the issue.