TCP/IPv4 - automatic IP and DNS setup don't work

[jsmith200]

I have a TP-Link TL-WR941ND router (192.168.0.1). A laptop is connected to it via a Ethernet cable. I have no internet connection if the Internet Protocol Version 4 of the laptop is set to obtain IP and DNS addresses automatically. If I login the router and use the ping function in the Diagnostic page in the System Tool to ping www.cnn.com, it works. That means the router has Internet connection but the laptop doesn't.

If I change the properties in Protocol Version 4 and set the IP to 192.168.0.99 and DNS to 192.168.0.1 and 10.10.10.10, then, the laptop has Internet access.

Meanwhile, cell phone has no Internet connection when connected to the router.

What could be the problem? The router had been working fine until this weekend.

 

[anotherdrew]

It sounds like the DHCP (the protocol that assignes IP addresses to devices that request one) is turned off or broken. Log into your router and look for DHCP. Did you get this router from someone else? They may have disabled it because they had another router providing DHCP. If you did get the router from someone else, you may want to do a factory reset and reconfigure the router.

 

[bskchaos]

DHCP is not enabled on the router. Seems that router is configured as an access point, connect the internet at port 1-4. Avoid using the WAN port.

 

[jsmith200]

It sounds like the DHCP (the protocol that assignes IP addresses to devices that request one) is turned off or broken. Log into your router and look for DHCP. Did you get this router from someone else? They may have disabled it because they had another router providing DHCP. If you did get the router from someone else, you may want to do a factory reset and reconfigure the router.

I checked the router's DHCP settings. It was enabled. The router was set to assign IP range from 192.168.0.100 to 192.168.0.199. There were 7 devices connected to the router. The IP ranged from 192.168.0.100 to 192.168.0.108 (105 and 106 were not assigned).

Strangely, in the DHCP clients list, I didn't find 192.168.0.99. The IP of the laptop was 192.168.0.104. I refreshed the list several times and got the same result. IPCONFIG showed the laptop's IP to be 192.168.0.99 which did not appear in router's DHCP client list.

A TV was among the 7 devices connected to the router. Although the TV had been turned off for several hours, it still showed up in the DHCP client list and clicking the refresh button to refresh the list did not change that. This and the laptop's IP made me think that the DHCP list was not refreshed regardless how many times I clicked the "refresh" button.

 

[jsmith200]

DHCP is not enabled on the router. Seems that router is configured as an access point, connect the internet at port 1-4. Avoid using the WAN port.

I did connect the laptop to port #4 on the router. And the DHCP server on the router was enabled.

 

[anotherdrew]

I checked the router's DHCP settings. It was enabled. The router was set to assign IP range from 192.168.0.100 to 192.168.0.199. There were 7 devices connected to the router. The IP ranged from 192.168.0.100 to 192.168.0.108 (105 and 106 were not assigned).

Strangely, in the DHCP clients list, I didn't find 192.168.0.99. The IP of the laptop was 192.168.0.104. I refreshed the list several times and got the same result. IPCONFIG showed the laptop's IP to be 192.168.0.99 which did not appear in router's DHCP client list.

A TV was among the 7 devices connected to the router. Although the TV had been turned off for several hours, it still showed up in the DHCP client list and clicking the refresh button to refresh the list did not change that. This and the laptop's IP made me think that the DHCP list was not refreshed regardless how many times I clicked the "refresh" button.

Very strange. Of the 7 devices connected to the router, are any the others a windows computer? If so, pull up a command prompt and do "ipconfig /release" and then "ipconfig /renew". Do the commands work? DHCP lease times can be hours or days and the it might be an issue only when a devices asks to refresh the DHCP information. I am not surprised the TV is listed as a client even though it is off. That is normal. Try unplugging the TV's Ethernet cable and then refreshing the list.

Of the 7 devices listed ... do any have internet connectivity?

I assume you have restarted your router.

 

[jsmith200]

Very strange. Of the 7 devices connected to the router, are any the others a windows computer? If so, pull up a command prompt and do "ipconfig /release" and then "ipconfig /renew". Do the commands work? DHCP lease times can be hours or days and the it might be an issue only when a devices asks to refresh the DHCP information. I am not surprised the TV is listed as a client even though it is off. That is normal. Try unplugging the TV's Ethernet cable and then refreshing the list.

Of the 7 devices listed ... do any have internet connectivity?

I assume you have restarted your router.

I have restarted the router several times with no avail. It is only after I reboot the router that the client list is updated, not showing the turned-off devices anymore. However, it doesn't show the laptop either even though the laptop has Internet connection. Another device that has Internet connection is a Samsung tablet. Two Huawei cell phones and another router don't have Internet connection.

 

[anotherdrew]

I have restarted the router several times with no avail. It is only after I reboot the router that the client list is updated, not showing the turned-off devices anymore. However, it doesn't show the laptop either even though the laptop has Internet connection. Another device that has Internet connection is a Samsung tablet. Two Huawei cell phones and another router don't have Internet connection.

The laptop is not showing because it is not getting it's address through DHCP, so therefore it is not a DHCP client. Clearly something has gone wrong in the routers software. I think it is time for a factory reset.

https://www.tp-link.com/ae/faq-497.html

If that does not work, you can manually assign IP addresses to your devices. I would also start looking around for a new router.

 

[BuddhaSkoota]

If I change the properties in Protocol Version 4 and set the IP to 192.168.0.99 and DNS to 192.168.0.1 and 10.10.10.10, then, the laptop has Internet access.

You stated that you set the IP to 192.168.0.99, therefore it would not show up in the router's DHCP list since you've manually assigned that address.

Also, I noticed that you have 2 private IP addresses set for DNS, but in different subnets. I'm wondering if that's intentional and if you inadvertently have 2 DHCP servers running on your network

 

[anotherdrew]

You stated that you set the IP to 192.168.0.99, therefore it would not show up in the router's DHCP list since you've manually assigned that address.

Also, I noticed that you have 2 private IP addresses set for DNS, but in different subnets. I'm wondering if that's intentional and if you inadvertently have 2 DHCP servers running on your network

192.168.0.1 as DNS makes sense. That is the router.
10.10.10.10 ... that is nothing (well, you can't get to it).

 

[jsmith200]

OK. Thanks. Now, I see why the laptop doesn't show up in the DHCP client list.

Regarding the DNS server, only 192.168.0.1 would suffice.

Well, I was suspecting there might be a hardware problem until I replaced the router with another one of the same model and the SAME THING happened again. I had to manually assign IP and DNS (well, not sure if I had to assign DNS server but I did it like before anyway) or there was no Internet connection. Things become more exciting now.

 

[anotherdrew]

For DNS you can toss in 8.8.8.8 (google DNS).

The router has been discontinued by TP-link ... maybe they put in a self destruct routine set for 6/20/2018 ... ok, I'm reaching, but that is how wacky this issue is. Brand new router does the same thing right out of the box? I'm lost ..... was going back and rereading all the posts. You said there was another router ... please explain.

 

[jsmith200]

For DNS you can toss in 8.8.8.8 (google DNS).

The router has been discontinued by TP-link ... maybe they put in a self destruct routine set for 6/20/2018 ... ok, I'm reaching, but that is how wacky this issue is. Brand new router does the same thing right out of the box? I'm lost ..... was going back and rereading all the posts. You said there was another router ... please explain.

Both routers are about 7 years old. They are not right out of box.

The topology of my network is like this:

ADSL modem -> router A -> two other routers

Two other routers are connected to router A. One has been turned off. So, on router A, only port #3 light is on (this is if I don't connect the laptop to router A.) All the three routers, router A, its replacement, and the one connected to port #3 are same model. To simplify trouble shooting process, I have pulled the cables so now no routers are connected to router A.

I have another two TP-LINK routers. I could use them to replace router A and see what happens but am hesitating to do that. Right now, two routers have the exact same problems. It seems like software problems.

 

[jsmith200]

OK. I reset the router to factory default and that cured the problem. Sorry to bother you guys for such a simple fix. Although I still don't understand why both routers had the same behavior, it doesn't matter now.

 

[anotherdrew]

[strike]So, you can have multiple router provide DHCP, but it can become an issue if they are on the same network (ie, if all your routers are at 192.168.0.1 then which one am I connecting to?). Best practice if your going to do it that way is have router A on 192.168.0.1 and B on 192.168.1.1 and C on 192.168.2.1. OR, turn DHCP off on routers B and C and let router A do all the DHCP (in this setup the best thing is also to not use the WAN port or B and C and just plug the line from A into LAN1 on both B and C. Then B and C become WiFi capable switches and router A is your only real router.)

So, what you have done is good. Make the network as simple as possible until things are working again. With the laptop being the only thing plugged into A, the laptop will work if you put in a manual IP address. What happens if you set the laptop to get an IP address automatically? You may have to use the commands "ipconfig /release" and "ipconfig /renew" to have it go and get new IP information. Are the commands successful. After the renew are you assigned an IP address in the DHCP range (100-199)? Can you connect to the internet? If you can not connect to the internet with "www.google.com", what happens if you put "172.217.9.142" into the browser address bar? If this works then the internet works, but your DNS does not.[/strike]

Woot ... glad it's fixed ... enjoy!