No dns sever?

[stubuzz]

The place where i live gets frequent power cuts. I have a router/access point in my room that is connected to the buildings main server and after the power goes off i sometimes cannot connect to the net though Ethernet because it is not getting auto dns sever allocation. It will say connected to the net but opening the browser shows a no dns error. However, i can connect and use the net on a WiFi connection. If i manually add the ipv4 address to the Ethernet connection in settings, it will work again.

 

Is the router faulty or could it be an ip address conflict? Any ideas?

 

 

 

[degrub]

Maybe there are multiple things going on. I’m assuming you are using MS Windows.

 

If, by manually entering a tcp/ip address for your device and changing “get address automatically “ to “ manual” , you restore access to the internet, that means that a router with a DHCP server is not active on your LAN AND the ip address lease on your device is uncommonly short duration. Your device should not be loosing its IP address just because of a power failure on the network. It retains its address until its address lease expires or it is rebooted.

 

If you are entering a tcp/ip address in the field “preferred dns server” or “alternate dns server”, then that indicates that the dns server you would normally access, either automatically or manually, is not reachable. 
 

So , figuring out where that failure is occurring depends on if the device in your room is a router or an access point.  Is the device provided by the building management or by you ?

Does building management provide the access to the internet or do you ?

 

If you go to windows start menu and enter cmd in the search box, select the cmd program entry and type 

ipconfig /all

it will return the details of all of your network configuration including your current ip address and lease expiration, DHCP server ip address,  DNS server addresses, and default gateway.

 

you can do this when everything is working and when it stops working to see what, if anything, has changed. You can run the PING command to determine if the ip address for the DHCP server, the DNS server, and the Gateway are reachable from your device.

 

ping 192.168.1.1 for example.

 

 

 

 

 

[stubuzz]

1 hour ago, degrub said:

 Is the device provided by the building management or by you ?

Does building management provide the access to the internet or do you ?

The device is provided by the building management. I think it is configured as an access point.

 

1 hour ago, degrub said:

DHCP server ip address,  DNS server addresses, and default gateway.

When working, the addresses for ethernet and wifi are the same, but not net connection when opening a browser on ethernet. If you manually change the dns address and save it the ethernet works for about 15 seconds. Note: the wifi connection works all of the while.

 

It seems that the only way to fix this is to to a hard reset on the main server and router. Then 9/10 times the problem will resolve itself.

[Tim K]

I'm confused do you lose DNS ip  or   your LAN adapter's IP?

You can set DNS by hand (Windows) once for the LAN adapter and it will never go away.

If you are losing LAN's ip which goes to 169.x.x.x (auto-generated if dhcp is not available) then you can also set it manually but pick the IP at the end range of the dhcp pool. like x.x.x.200 or x.x.x.150.  Shouldn't cause a conflict.
Of course set it to the same values as when everything is working.

too big MTU value can also cause HTTP traffic to break while other software keeps working fine (ICQ/SKYPE/ torrents/ ftp).

also try disabling tcpip v6 for LAN adapter.

[shdmn]

Just configure your computer to use Google DNS servers.

 

On Windows go into Control Panel > Network and Internet > Network and Sharing Center > Network connection settings > Properties > click on TCP/IP4 then click on "Properties" button.

 

Change "Obtain DNS server address automatically"

to

"Use the following DNS server addresses"

8.8.8.8
8.8.4.4

 

 

[beautifulthailand99]

I do

 

cmd and at the dos prompt

 

ipconfig /flushdns

ipconfig /release

ipconfig /renew which always seems to work for me.

[shdmn]

10 minutes ago, beautifulthailand99 said:

I do

 

cmd and at the dos prompt

 

ipconfig /flushdns

ipconfig /release

ipconfig /renew which always seems to work for me.

That probably won't fix this problem because it appears to be due to DHCP on the router they are connecting to and/or the ISP.  Manually adding Google DNS IPs on their computer will fix those sorts of problems.  It may also increase DNS lookup speed, so not a bad idea to do it even if not having problems.

[beautifulthailand99]

3 minutes ago, shdmn said:

That probably won't fix this problem because it appears to be due to DHCP on the router they are connecting to and/or the ISP.  Manually changing the DNS IP used on their computer to the Google DNS servers will fix all those sorts of problems.

Thanks I keep getting this problem and this fixes it or seems to do you know if it's just luck. It happens virtually every week.

[cjinchiangrai]

I used to have this regularly when the router would reboot and assign a default IP before the switch rebooted. If you unplug the router for a few seconds it should reacquire the IP after a power failure.

[KhunHeineken]

3 hours ago, shdmn said:

Just configure your computer to use Google DNS servers.

 

On Windows go into Control Panel > Network and Internet > Network and Sharing Center > Network connection settings > Properties > click on TCP/IP4 then click on "Properties" button.

 

Change "Obtain DNS server address automatically"

to

"Use the following DNS server addresses"

8.8.8.8
8.8.4.4

 

 

Go one further and set the DNS in the router. 

 

Cloudflare is ok. 1.1.1.1. 

 

It's reported as being the fastest.