Temporary Loss of DNS Server

[Thczv F. Thczv]

I run an RT-AC66U with ASUSWRT-Merlin 378.55 as my main router with the connection to the internet. This router provides DHCP for all of the devices on the network, and also provides WIFI. It seems to work fine, except that it is a bit far from my desk. I also run a R7000 with XWRT-Vortex 378.56_2 as a separate WIFI access point only. The R7000 access point connects to the AC66U for internet access. When it works it is great, and much faster than the AC66U. But when I connect via WIFI to the R7000, periodically my PC forgets how to find the DNS server, and the internet stops working. It usually gets restored within a few minutes. When I connect to the AC66U, my PC always remembers how to find the DNS server.

Any idea how to troubleshoot this? I already cleared the settings and reconfigured the R7000 once. I'm not sure how to figure this out.

Thanks,
Dave

 

[coxhaus]

Why not switch the routers around and see if the problem changes or goes away?

 

[Thczv F. Thczv]

Why not switch the routers around and see if the problem changes or goes away?

That could be worth a try. Do you happen to know whether it is possible to save and restore settings between these different units? The firmware is very similar.

 

[Zirescu]

On the R7000, is it configured DHCP back to the AC66U or Static?

 

[Thczv F. Thczv]

On the R7000, is it configured DHCP back to the AC66U or Static?

The R7000 is configured static. I could try using DHCP back to the AC66U. That would be an easy one to test.

 

[ColinTaylor]

But when I connect via WIFI to the R7000, periodically my PC forgets how to find the DNS server, and the internet stops working.

What do you mean exactly by "forgets how to find the DNS server"? It sounds like you have lost all network connectivity rather than just the route to DNS.

Look in the system logs of the PC for the time the problem occurs. Are there any errors? Does the network disconnect?

If there is nothing obvious, try the following while the problem is happening:

1) ping the IP address of the access point to confirm you are still connected to it.
2) ping the IP address of the router to confirm the access point is connected to the router.
3) ping 8.8.8.8 to confirm the router is still connect to the internet.
4) ping the IP address of whatever DNS server the router is configured to use.

If all the above are OK post the complete (unedited) output of the following command from the PC (assuming it's Windows):

ipconfig /all

 

[Thczv F. Thczv]

ColinTaylor, you are right. It is the loss of all network connectivity, rather than just the DNS. It just manifest as the loss of DNS because that is the network service that fails most often when I am trying to access the internet. I confirmed that when the problem happens, I can't ping even the access point, much less anything beyond. Following up on what Zirescu said, I also tried using DHCP for the access point, rather than static settings. That didn't help. In my troubleshooting, I ruled out a Windows configuration problem because my PC connects to the router's wifi just fine. But in case it helps, here is the output (below) from ipconfig /all.

Windows IP Configuration

Host Name . . . . . . . . . . . . : Thczv-Laptop
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : RCI.lan

PPP adapter rcivpn:

Connection-specific DNS Suffix . : RCI.lan
Description . . . . . . . . . . . : rcivpn
Physical Address. . . . . . . . . :
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 192.168.16.65(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . :
DNS Servers . . . . . . . . . . . : 192.168.16.3
NetBIOS over Tcpip. . . . . . . . : Enabled

Ethernet adapter Local Area Connection 2:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : TAP-Windows Adapter V9
Physical Address. . . . . . . . . : 00-FF-99-16-EF-4F
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes

Wireless LAN adapter Wireless Network Connection 3:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft Virtual WiFi Miniport Adapter #
2
Physical Address. . . . . . . . . : 84-A6-C8-7F-0D-6A
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes

Wireless LAN adapter Wireless Network Connection 2:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft Virtual WiFi Miniport Adapter
Physical Address. . . . . . . . . : 84-A6-C8-7F-0D-6A
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes

Wireless LAN adapter Wireless Network Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel(R) Centrino(R) Wireless-N 2230
Physical Address. . . . . . . . . : 84-A6-C8-7F-0D-69
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::20da:30a4:b1ad:5a3b%18(Preferred)
IPv4 Address. . . . . . . . . . . : 192.168.1.200(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : Thursday, January 14, 2016 8:55:20 AM
Lease Expires . . . . . . . . . . : Friday, January 15, 2016 11:04:52 AM
Default Gateway . . . . . . . . . : 192.168.1.1
DHCP Server . . . . . . . . . . . : 192.168.1.1
DHCPv6 IAID . . . . . . . . . . . : 444901064
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-18-37-A5-E0-84-A6-C8-7F-0D-69

DNS Servers . . . . . . . . . . . : 8.8.8.8
8.8.4.4
NetBIOS over Tcpip. . . . . . . . : Enabled

Tunnel adapter isatap.{C529F218-7CD3-473F-88D8-0851FC12413A}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft ISATAP Adapter
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Tunnel adapter isatap.{B696AC4A-CFFD-48FD-BC15-4FF0EAEB7761}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft ISATAP Adapter #2
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Tunnel adapter isatap.{9916EF4F-573C-492B-A6E7-7FE4B2C6C11F}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft ISATAP Adapter #3
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Tunnel adapter isatap.{ECA2E916-630B-4EE6-9A1A-9E91B4AA8C96}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft ISATAP Adapter #4
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Tunnel adapter isatap.RCI.lan:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . : RCI.lan
Description . . . . . . . . . . . : Microsoft ISATAP Adapter #5
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

 

[ColinTaylor]

ColinTaylor, you are right. It is the loss of all network connectivity, rather than just the DNS. It just manifest as the loss of DNS because that is the network service that fails most often when I am trying to access the internet. I confirmed that when the problem happens, I can't ping even the access point, much less anything beyond. Following up on what Zirescu said, I also tried using DHCP for the access point, rather than static settings. That didn't help. In my troubleshooting, I ruled out a Windows configuration problem because my PC connects to the router's wifi just fine. But in case it helps, here is the output (below) from ipconfig /all.

OK. When you lose connectivity to the access point what do you see in the Windows Event Log? Do you see the wireless network adapter disconnecting from the access point, or does it think it is still connected?

What about the wireless icon in the Windows taskbar? Is it showing as connected, disconnected, searching, etc?

 

[Thczv F. Thczv]

OK. When you lose connectivity to the access point what do you see in the Windows Event Log? Do you see the wireless network adapter disconnecting from the access point, or does it think it is still connected?

What about the wireless icon in the Windows taskbar? Is it showing as connected, disconnected, searching, etc?

At first the wireless icon doesn't change. I see network problems (VPN drops, DNS lookups fail, etc) before the wireless icon changes. Eventually the wireless icon will change and show a yellow exclamation point. Network status typically shows that I am connected to the network, but don't have internet access. Though, as I said, I can't ping the access point. The Windows event viewer mainly shows warnings about DNS lookups failing. I get some errors about Secure Socket Tunneling Protocol failing to connect, which I think is the VPN failing.

 

[ColinTaylor]

I am suspecting that it might be a VPN issue (I hadn't realised you were using a VPN).

It would not be that unusual that you can't ping the access point if the VPN is active. Unless you have split tunnelling configured the ping would be routed through the VPN.

Do you use the VPN all the time? If not, does the problem only occur when the VPN is active?

 

[Thczv F. Thczv]

I am suspecting that it might be a VPN issue (I hadn't realised you were using a VPN).

It would not be that unusual that you can't ping the access point if the VPN is active. Unless you have split tunnelling configured the ping would be routed through the VPN.

Do you use the VPN all the time? If not, does the problem only occur when the VPN is active?

I did a bunch of additional troubleshooting to see if the VPN makes a difference. FYI, I do have split tunneling configured. But when I left the VPN inactive for a couple of days (over the weekend) and kept pinging the DNS every 5 seconds, I didn't have any network drops. Once I activated the VPN, I did get some network outages. But here is what is really odd: If I connect to the router's wifi (rather than the AP wifi), and activate the VPN, I have no problem at all with network outages. That makes me think it isn't a problem with my VPN settings. Is there some reason why a R7000 with XWRT-Vortex 378.56_2 (operating as an access point) would freak out over a VPN, whereas an RT-AC66U with ASUSWRT-Merlin 378.55 (operating as a router) wouldn't? Aren't those firmwares very similar?

 

[ColinTaylor]

Are there any clues in the XWRT-Vortex's syslog? Apart from that I can't help you. Have you tried asking the XWRT-Vortex developer?

 

[sfx2000]

I did a bunch of additional troubleshooting to see if the VPN makes a difference. FYI, I do have split tunneling configured. But when I left the VPN inactive for a couple of days (over the weekend) and kept pinging the DNS every 5 seconds, I didn't have any network drops. Once I activated the VPN, I did get some network outages. But here is what is really odd: If I connect to the router's wifi (rather than the AP wifi), and activate the VPN, I have no problem at all with network outages. That makes me think it isn't a problem with my VPN settings. Is there some reason why a R7000 with XWRT-Vortex 378.56_2 (operating as an access point) would freak out over a VPN, whereas an RT-AC66U with ASUSWRT-Merlin 378.55 (operating as a router) wouldn't? Aren't those firmwares very similar?

Hmmm... Am I the only one that sees a very large security issue here?

Running a Router/AP as a VPN client totally bypasses all the firewall goodness and NAT protections that most SOHO routers provide, opening the entire LAN to the internet for inbound traffic...

Wow...

 

[ColinTaylor]

Er, I'm not sure I understand you. If I understand correctly the VPN client is running on his Windows PC not the router/AP. See post #7 "PPP adapter rcivpn".

 

[onepush]

Can I piggyback off this thread?

I'm using a VPN client (PIA) and under Redirect Internet traffic - I have it set to all traffic. In my WAN settings I've input my VPN's DNS IP addresses, but should I also input these DNS servers under "DHCP Server" configuration n the LAN tab?

Right now the setting says "enabled the DHCP server" and has a range of 2-254. But, there are no IP addresses in DNS Server 1/DNS Server 2.

I want to make sure all devices connected to my router go through the VPN (as well as all traffic).

EDIT: Also in response to sfx2000, I followed this guide to setup my Router: https://vpntips.com/vpn-router-install/

Should I have set up a VPN server instead? I'm a complete n00b obviously.

 

[Thczv F. Thczv]

I think I figured out my problem. It was actually a combination of problems. #1, a seldom used network printer (that wasn't even accessible via wifi) was setup to use 192.168.1.200. #2, even though I set my PC to use DHCP, there was a hidden preference for 192.168.1.200 (which I first noticed after ColinTaylor suggested I past ipconfig /all. Thanks!). So whenever I connected to the same network that the printer was using (hosted by the AP), there was an IP address conflict that caused the network to drop periodically. It took a little research to figure out how to clear old IP address preferences ("netsh winsock reset catalog", "netsh int ip reset reset.log"). Now I expect the problem to go away. Thank you all for your efforts.

 

[ColinTaylor]

Great detective work there! I hope that solves all your problems.

My assumption is that Windows "preferred" IP address is just the one it got from DHCP the last time. So that the next time it will ask for the same address. Of course it's up to the DHCP server to decide whether it will give out that address or not. So theoretically, if one device got 192.168.1.200 from DHCP and then the router was rebooted, another device could subsequently ask for an address and also be given 192.168.1.200 because the router has no memory of having given out that address.

I guess this is only a problem when a device is connected to an access point because any devices connected to the router would have their network connections refreshed if the router was rebooted. Devices connected to the access point would be unaware that anything had happened.

 

[Thczv F. Thczv]

I think the network printer was manually set to use 192.168.1.200 as a static IP, which is why the conflict kept persisting. That printer is proving difficult to reconfigure. But the problem should go away now that I have my PC set to use a different IP. Crossing fingers.