I have been seeing periodic drops in internet access from LAN connected devices lately (last 2 months), and I haven’t been able to figure about exactly what is going on. There doesn’t seem to be a pattern, and it resolves itself after a few hours.
- I can access the internet from my router
- All devices on LAN can reach each other, both wired and WiFi
- All devices on LAN can reach router, both wired and WiFi
- I haven’t changed anything in router settings
- I haven’t added new devices to my local network
- I can’t find any IP conflicts
- It’s a simple flat network with two APs, a single switch, no VLAN separation
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Lots of good suggestions here already but what is your upstream DNS provider and is it your ISP DNS from DHCP?
Sounds to me like your DNS on the router itself is crashing.
There’s a couple of things you could do. Set up something like pihole or adguard home, and set the forwarding to something other than your internal DNS server.
Personally, I use AGH, and the default quad9 for forwarding all but my own domains. Those get handled by my OPNsense router’s Unbound DNS and/or DNSMasq, depending on which domain (local or one of owned domains)
Everything other than those gets forwarded to quad9’s public DoH service.
The basic workflow of network troubleshooting is:
- Check if it’s a DNS problem
- If not, check why it is a DNS problem anyway, but you failed to recognize it.
I mean, i have narrowed it down to some kind of DNS issue, I just don’t know what. Right now everything is working again (I haven’t changed anything), so I’ll have to keep looking next time it stops working. It’s just weird it works for days/weeks at a time, and then suddenly breaks for a few hours until it “magically” fixes it self again without me doing anything.
When this happens, can you ping something on the internet from LAN using ip address and not a dns name ?
If it works, it could be an issue on the dns side (not reachable or not answering)From my laptop I can ping outwards using IP, but not names (e.g. openwrt.org), but I can reach my DNS from my laptop
From my laptop I can ping outwards using IP, but not names (e.g. openwrt.org), but I can reach my DNS from my laptop
Okay, well, that’s a pretty good indication that marud’s guess is right and it’s DNS-related, if you can reach hosts by IP but not by name. Is the laptop Linux?
Is the laptop Linux?
It is yes
Okay. It’s going to be a little harder to diagnose it since the problem isn’t immediately visible, but you’ve got all the Linux toolset there, so that’s helpful.
Is the DNS server you’re trying to use from the LAN machines running on the OpenWrt machine, or off somewhere on the Internet?
EDIT: Or on the LAN, I guess.
EDIT2: Oh, you answered that elsewhere.
I am using my routers DNS, and it’s reachable from my laptop.
Have you tried doing a DNS lookup from the router (pinging a host by name, say) when you were having the problems?
If so and it didn’t work, that’d suggest that the problem is the upstream DNS server. If that’s the problem, as IsoKiero suggests, you might set the OpenWrt box to use a different DNS server.
If so, and it worked, that’d suggest that the issue is the OpenWrt host’s DNS server serving names. It sounds like OpenWrt uses dnsmasq by default.
If not…that’d probably be what I’d try next time the issue comes up.
Have you tried doing a DNS lookup from the router (pinging a host by name, say) when you were having the problems?
Yes this works when I’m having issues. I guess I’ll try looking in to my routers DNS next time i have issues. For now it’s working again (I still haven’t changed anything)
Yes this works when I’m having issues.
Okay, gotcha. In that case, my guess is that the most-likely issue is with the DNS daemon that OpenWRT is using, which is most-likely dnsmasq.
You could confirm that your DNS configuration on the LAN hosts is actually using OpenWRT as the DNS server if you wanted — I could walk through that, if you’re not sure. But from a test-when-it’s-happening situation, I’d probably:
-
Install
digon the Mint box, if it’s not already installed. That’s a DNS diagnostic program that doesn’t use your system resolving mechanism, talks directly to DNS, so it cuts out any other factors. It’ll be in the bind9-dnsutils package.$ sudo apt install bind9-dnsutils -
Install
digon the OpenWRT box.$ opkg update $ opkg install bind-dig -
Confirm that you can successfully run it on both the OpenWrt box and your laptop when there are no problems (your router’s LAN address probably being something like 192.168.1.1):
$ dig @your-router-LAN-address www.google.com -
Confirm that you can successfully run it on both the OpenWrt box and your laptop when there are no problems using whatever outside DNS server you have the OpenWrt box set to use (assuming 1.1.1.1 here):
$ dig @1.1.1.1 www.google.com -
Next time you have problems, repeat the above. If both the
digon your OpenWrt box and on your laptop using the OpenWrt DNS server now fail, then it’s probably pretty safe to say that it’s the DNS server on the OpenWrt box at fault. If just the one on your laptop fails, then it’s going to be a communication issue between your LAN box and the OpenWrt DNS server.
Assuming that the problem is the OpenWrt DNS server, and assuming that it’s dnsmasq, to troubleshoot further, I might try looking at its logs, or installing
tcpdumpon the OpenWrt box and running that, something like$ tcpdump -nvvv -i any udp port domain. That should let you see both the incoming DNS queries going to the OpenWrt DNS server as well as the queries that it is sending upstream (the-nwill preventtcpdumpfrom itself sending DNS queries to look up IP addresses, which would generate more noise, the-vvvto show all possible information about the packets, and the-i anyto show all packets on all interfaces). That’ll let you see whether it’s getting flooded with DNS queries and to see what queries it’s sending to the upstream DNS server out on the Internet.That won’t alone solve your problem, but it’d be the next step I’d try to narrow down what’s going on.
-
I’m not sure what you mean when you say that you’re seeing “periodic drops”. Like, you’re sending pings from a wired-LAN device to somewhere on the Internet and not getting a response? Inbound TCP connections from the Internet aren’t being forwarded to a device on the LAN?
Internet access from all devices in my house simply stops working entirely for a few hours, sometimes there’s weeks between this happening, sometimes only a few days. But when this happens, I can still reach internet from my router without issue.
Does restarting your router help in these moments? Might just be an underpowered router
Do your devices use the router’s DNS? If so is it still reachable? From the client? From the router machine?
Might be some kind of DHCP bug too but I’m not well versed in it
Restart doesn’t fix it unfortunately.
I am using my routers DNS, and it’s reachable from my laptop.
If you’re using your router as DNS, it’s using something else as DNS. Check those configs. One entry might be invalid or intermittently down. Try switching to another provider.
Also check that you’re actually using the router as the DNS. When you do an nslookup you can specify DNS server. Next time you have the issue try
Nslookup example.com 9.9.9.9
If that replies then it’s not a network issue it’s your DNS config, either locally or on the router itself.
Okay. So, I don’t know exactly what you’re doing to test that, but I’m going to assume, say, trying to go somewhere in a Web browser.
First off, I have occasionally seen problems myself where consumer broadband routers that have been on for a long time wind up briefly becoming unresponsive. Probably some sort of memory leak or something. So if you haven’t rebooted the thing and seen whether all your problems magically stop showing up, I’d probably try that. Quick and easy.
Okay. Say that doesn’t do it.
When you confirm that the router can reach the Internet during this period of outage, how are you doing that? Going to a management Web UI from a wired-LAN device and trying to ping some host on the Internet?
When you confirm that the router can reach the Internet during this period of outage, how are you doing that?
it’s a gl.inet brume2 running openwrt, I SSH into it and can ping outwards to anything and my speed test from the CLI tells me i have 900Mbit available
Ah, gotcha, cool. If it’s OpenWrt and you have shell access, that should make it easier to diagnose. When you are checking that you don’t have connectivity from your local LAN device, you tried pinging the same out-there-on-the-Internet host, and that failed?
Yes I use the same destination fro testing on my laptop and the router.
I think I’ve narrowed it down to a DNS issue, I just don’t know exactly what. I can ping outwards from my laptop when using IPs but not names. But my laptop can reach my DNS.
For whatever reason ISPs tend (at least in here) to be pretty bad at keeping their DNS services up and running and that could cause issues you’re having. Easy test is to switch your laptop DNS servers to cloudflare (1.1.1.1, 1.0.0.1) or opendns (208.67.222.222, 208.67.220.220) and see if the problem goes away. Or even faster by doing single queries from terminal, like ‘dig a google.com @1.1.1.1’.
If that helps you can change your router WAN DNS server to something than what operator offers you via DHCP. I personally use opendns servers, but cloudflare or google (8.8.8.8, 8.8.4.4) are common pretty decent choices too.
How is your DNS configured / implemented?
Just default for my gl.inet, haven’t changed anythingon that part.
Given that you’re having issues with the DNS, I’d look at this.
Specifically, are you using the ISP DNS as an upstream lookup, or have you configured another DNS as the upstream?
Is the ISP DNS locking you out because you’re hammering it?
Does the ISP block traffic on Port 53?
When you’re having issues, can you look up addresses using a different DNS?
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I’ve seen in this thread:
Fewer Letters More Letters DHCP Dynamic Host Configuration Protocol, automates assignment of IPs when connecting to a network DNS Domain Name Service/System IP Internet Protocol SSH Secure Shell for remote terminal access TCP Transmission Control Protocol, most often over IP
5 acronyms in this thread; the most compressed thread commented on today has 12 acronyms.
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