Question Repeated Disconnects; Can't Reach DHCP Server ?

[BenWVU]

Up until several weeks ago, I had no internet issues. I frequently lose internet access to all of my devices, now; wired and wireless.

My browsers and Windows network adapter diagnosis say that the DHCP server can't be reached.

I use an Arris SB8200 modem and a TP-Link Archer C7 v4.0 router. My desktop is hardwired to the router.

I have tried the following:

• Rebooting the router (no change)
• Connecting the desktop directly to the modem (no change)
• Using a different router (no change)
• Using a different modem (no change)
  • I used a new modem for a week and returned it after the first disconnect happened.
• Calling the ISP (no problem identified)
• Having an ISP tech visit (no problem identified)
  • He checked the coax cables and grounding. Of course, the internet was fine while he was here.
• Rebooting the modem (this usually works, but the problem returns in anywhere from a week to 5 minutes)

I'm going nuts. What should my next step be? What could be the root cause?

 

[kanewolf]

Up until several weeks ago, I had no internet issues. I frequently lose internet access to all of my devices, now; wired and wireless.

My browsers and Windows network adapter diagnosis say that the DHCP server can't be reached.

I use an Arris SB8200 modem and a TP-Link Archer C7 v4.0 router. My desktop is hardwired to the router.

I have tried the following:

• Rebooting the router (no change)
• Connecting the desktop directly to the modem (no change)
• Using a different router (no change)
• Using a different modem (no change)
  • I used a new modem for a week and returned it after the first disconnect happened.
• Calling the ISP (no problem identified)
• Having an ISP tech visit (no problem identified)
  • He checked the coax cables and grounding. Of course, the internet was fine while he was here.
• Rebooting the modem (this usually works, but the problem returns in anywhere from a week to 5 minutes)

I'm going nuts. What should my next step be? What could be the root cause?

What do the LEDs on the router show when you have an outage?

 

[BenWVU]

What do the LEDs on the router show when you have an outage?

Red for internet, otherwise green.

Modem lights are all green and blue; normal.

 

[stonecarver]

Okay quick question did you swapped out the power brick for modem. Yes it seems like a stupid question to ask but sometimes that's the fix. I can't tell you how many times this really is the issue. If you did change it out at least we can cross that out.

 

[kanewolf]

Red for internet, otherwise green.

Modem lights are all green and blue; normal.

You need to open a cmd.exe window and run ipconfig.exe /all
That will provide a snapshot of your network adapter status. Do it once when you have no issues and save it. Then repeat when you are having issues.
Post both screen shots to imgr or some hosting site.

 

[BenWVU]

You need to open a cmd.exe window and run ipconfig.exe /all
That will provide a snapshot of your network adapter status. Do it once when you have no issues and save it. Then repeat when you are having issues.
Post both screen shots to imgr or some hosting site.

I was able to check this the last time it happened. The output during and after the interruption was identical...

 

[kanewolf]

I was able to check this the last time it happened. The output during and after the interruption was identical...

If they are the same, then your "DHCP server can't be reached", may be a false diagnosis.

 

[BenWVU]

If they are the same, then your "DHCP server can't be reached", may be a false diagnosis.

That was my thought, too.

I did a factory reset and reconfigured the router and am crossing my fingers, but I don't have high hopes.

One of my tested routers is an older TP Link Archer C7, but the other is an Asus GT-AC2900 that is less than a year old. I would be surprised if both decided to die at the same time, however, neither perform like they should; the Asus has a known defect with its 2.4 GHz radio and the Archer seems to have faulty 5 GHz, starting today. Of course, my desktop is hard wired, so all of that should all be irrelevant.

I still might pick up another router and try it for a while (and return it if the issue crops up, again, like I did a modem). Part of me thinks it's on my ISP's side, even though they haven't been able to identify anything.

 

[bill001g]

It is not going to be on the ISP side. DHCP is only used on your lan between your router and the pc. Even then there is almost no traffic. DHCP is only used when the pc first boots and then again when you hit 1/2 the reservation time. Most people set the dhcp reservation time to a few days if not a week. Still you will not see messages generally at 1/2 the time it might put a error in the event log but it continues to function until the time actually completely expires.

The brute force approach to hide any dhcp issue is to just use a fixed/static IP on your pc and not use DHCP.

DHCP is also many times used between your router and the ISP. The same process is done but you will not see a message on your pc it might be on the router or maybe the modem since it is kinda involved. If you look at the modem logs it will show if there is any issue with the internet connection.

Are you sure it was a DHCP message and not DNS. DNS ones are more common and they generally mean the internet went down.

 

[BenWVU]

It is not going to be on the ISP side. DHCP is only used on your lan between your router and the pc. Even then there is almost no traffic. DHCP is only used when the pc first boots and then again when you hit 1/2 the reservation time. Most people set the dhcp reservation time to a few days if not a week. Still you will not see messages generally at 1/2 the time it might put a error in the event log but it continues to function until the time actually completely expires.

The brute force approach to hide any dhcp issue is to just use a fixed/static IP on your pc and not use DHCP.

DHCP is also many times used between your router and the ISP. The same process is done but you will not see a message on your pc it might be on the router or maybe the modem since it is kinda involved. If you look at the modem logs it will show if there is any issue with the internet connection.

Are you sure it was a DHCP message and not DNS. DNS ones are more common and they generally mean the internet went down.

I'm certain that my browser flags it as a DHCP error, not DNS.

My desktop (which goes offline along with everything else when this happens) has been assigned a fixed IP.

My modem never has any error logs when this happens. Its status lights never change either.

All of that points to it being a router issue, but I've been testing, resetting, and getting interruptions using two different routers...

 

[bill001g]

A browser should never see dhcp it would be a message from windows. Check the event viewer.

If you have a fixed IP you are not using DHCP so you can never get DHCP errors.

 

[BenWVU]

A browser should never see dhcp it would be a message from windows. Check the event viewer.

If you have a fixed IP you are not using DHCP so you can never get DHCP errors.

I'm certain that's what the error message was (accurate or not) because I wrote it down before it started working again.

I gave the Windows troubleshooter a shot and I'm pretty sure it said the same thing.

I'll need to check the Event Viewer.

 

[BenWVU]

A browser should never see dhcp it would be a message from windows. Check the event viewer.

If you have a fixed IP you are not using DHCP so you can never get DHCP errors.

There's only one event close to the time that this happened last, but it happened about 10 minutes earlier, so I'm not sure it's even relevant.

Event

Also, here is a message from my router's page, during one of the interruptions, stating that it's an ISP DHCP problem. I forgot that I saved it.

Router Page

 

[bill001g]

That makes a little more sense. The pc is not losing the DHCP the router is.

The pc is losing DNS but that is a stupid message because the whole internet connection is down so of course you can't see the DNS server,along with every other site on the internet.

It is not likely a actual DHCP message. It could in theory be that the ISP had their DHCP server function go down and the wan IP happened to hit the DHCP renewal limit while the server was down. It is much more likely the whole internet connection dropped and the router attempted to reconnect while it was still down. Since it could not get a IP address you get that warning but it does not really mean just the DHCP server was down.

Get into the modem and see what it says. The modem IP should be 192.168.100.1. I bet the internet dropped.

 

[BenWVU]

That makes a little more sense. The pc is not losing the DHCP the router is.

The pc is losing DNS but that is a stupid message because the whole internet connection is down so of course you can't see the DNS server,along with every other site on the internet.

It is not likely a actual DHCP message. It could in theory be that the ISP had their DHCP server function go down and the wan IP happened to hit the DHCP renewal limit while the server was down. It is much more likely the whole internet connection dropped and the router attempted to reconnect while it was still down. Since it could not get a IP address you get that warning but it does not really mean just the DHCP server was down.

Get into the modem and see what it says. The modem IP should be 192.168.100.1. I bet the internet dropped.

The modem only has two events logged during that time period, but I can't even be sure what time they were logged. For some reason it lost track of what time it was for a while and logged timestamps from the 1970's. All I know is these are the only ones logged between 6/28 and today.

"Honoring MDD; IP provisioning mode = IPv4"

"SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

Edit: Also note that the modem lights never change to indicate a problem during the interruptions.

 

[bill001g]

The sync message means the modem had issues talking to the ISP equipment. It likely had a small outage but generally you will see lots of these messages when it is having a bigger issue.

Hard to say but if the router is complaining about not getting DHCP messages from the ISP that is a ISP problem.