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Connection drops for a few seconds intermittently

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jaroop
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Connection drops for a few seconds intermittently

We recently migrated to a new office and now have a Comcast-provided Cisco DPC3941B powering our network, connected to two gigabit switches (HP V1910, 1920), a VoIP gateway with an IPv4 public static IP, and two access points (re-purposed netgear routers in AP mode).

 

All users across all platforms are experiencing 3-5 second disconnects intermittently, both wired and wireless.  Happens even with a direct connection to the DPC3941B.

 

Tried to do some troubleshooting with WireShark, PingPlotter and the only issues I can see is a fair amount of packet loss to the first hop after our modem ONLY via IPv6.. could this be the cause of the issue? Clients that disable IPv6 seem to encounter the issue less often, but it does not correct it entirely.

 

Below are plots to google.com and comcast.net via IPv6 showing roughly 30-40% packet loss on the 2nd hop: www.google.com2.png

 

www.comcast.net.png

 

 

Appreciate any insight someone might have or pointers in the right direction as to other things we can troubleshoot. Thanks!

Accepted Solution

Re: Connection drops for a few seconds intermittently

We've had several techs come out, and have been escalated to 'tier 2' twice now.  First time they labeled it an area issue, and that it would be fixed.  After no results, reaching out to them revealed that said 'area issue' didn't even apply to us.

 

Asked me to gather data about connection drops, I wrote a simple script that curl'd www.comcast.net continuously and logged when it was unable to.  The data suggests that our connection drops almost every 5 minutes like clockwork.

 

I'm fairly positive that they never deauthorized our static IP when we moved from one location to another, and we're getting a conflict, but no one believes me.

 

Thoughts?

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Accepted Solution

Re: Connection drops for a few seconds intermittently

I'm having this problem too.

 

Here's my setup: I have a 5 static IPs on this connection. I have 4 servers and a router for the rest of my network.

 

I can start a ping on my static IP gateway and get about 40% packet loss. I tried running this ping from my workstation (through my router), from one of my servers (directly connected to the modem) and from my router (also connected directly to my modem). They all show the same behavior and they all start dropping packets at the same time.

 

Here's another interesting issue: whenever I try to connect to my modem's web interface (10.1.10.1), whenever I see packet loss, the modem's web interface also stops responding. I tried changing the cable between my modem and my router, same problem. I tried connecting my laptop directly to the modem and I still get the same problem.

 

I can ping anything within my local network and I have no problem. I can also ping my server's external IP addresses and have no problem either.

 

Now, I know that before I upgraded my internet connection, we had a 50mpbs connection with a Netgear modem. And when I logged in to the Netgear modem, the WAN address was a random IP address assigned from their DHCP. It was my understanding that any static IP routing was happening through a tunnel that was configured between the device and their network and everything was being tunneled through that IP, assigned by their DHCP server. Now, that Cisco modem is showing its WAN IP address to be my static IP's gateway. Maybe the modem has different capabilities, I don't know, but I never had any issue with the Netgear modem before.

 

Anyone else ever had an issue like that?

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8 REPLIES
Trusted Forum Contributor

Re: Connection drops for a few seconds intermittently

Since the loss isn't continuing on down the trace that isn't your issue, which is excellent as addressing packet loss issues with Comcast is pain..

 

Can you go to http://10.1.10.1/ and post your modem signal levels for us? Ideally, try to grab them while users are experiencing the issue and while it has subsided. 

jaroop
Visitor

Re: Connection drops for a few seconds intermittently

I will try and get these values when the issue happens, but disconnects are so short (and the Cisco so slow at loading pages normally) that it's difficult.  It might be noteworthy that during any downtime I can ping the gateway and any other host on the local network, DNS and general outbound connectivity are what fails (IM clients disconnect, etc.)

 

Screen Shot 2016-01-07 at 9.39.30 AM.png

jaroop
Visitor

Re: Connection drops for a few seconds intermittently

We've had several techs come out, and have been escalated to 'tier 2' twice now.  First time they labeled it an area issue, and that it would be fixed.  After no results, reaching out to them revealed that said 'area issue' didn't even apply to us.

 

Asked me to gather data about connection drops, I wrote a simple script that curl'd www.comcast.net continuously and logged when it was unable to.  The data suggests that our connection drops almost every 5 minutes like clockwork.

 

I'm fairly positive that they never deauthorized our static IP when we moved from one location to another, and we're getting a conflict, but no one believes me.

 

Thoughts?

PreventRage
New Member

Re: Connection drops for a few seconds intermittently

This seems very close to familiar.

 

Starting a few weeks ago the internet would appear to disappear from all devices (wired or wireless) on our LAN. LAN connectivity was fine. In my case the outgage would be every hour or so (not regular) and would last for anywhere from a minute to ten minutes.

 

I think you're way ahead of me on tool knowledge. I just opened a couple of command prompts and typed ping -t 75.75.75.75 in one of them and ping -t 75.75.76.76 in the other. Every once in a while one of them has a single ping time out. Presumably nothing. And then every once in a while they both disappear for a period of several minutes.

 

First interesting bit though. During the disconnect moments I can still connect to the little website in the cable modem. And if I from go to the test....

 

Ooh. Right there. It's just broke. Now this very website is in the awkward offline mode.

 

And now we're back. About three minutes.

 

.. anyway. If I do ping tests from within the cable modem during the "outage" they always work. I've removed all intervening switches - my whole site is now just the cable modem and two PCs plugged directly into it.

 

 

jaroop
Visitor

Re: Connection drops for a few seconds intermittently

Super interesting, glad we're not alone.  A co-worker was in the office this weekend and noticed less drops with only a few devices connected and actively using the network, could you tell me how many devices you have connected on average? We have around 40. However, this theory isn't super sound as I have tried it with a single device and none of our equipment attached and still got the drop.

 

What geographical area are you in?

 

If we're both experiencing the issue.. and we're not in the same geo area, I'm gonna guess it's these Cisco gateways.. I'm at my wit's end, over here.

 

 

jmaslak
New Contributor

Re: Connection drops for a few seconds intermittently

If you have only one IP, the modem is still doing NAT.

 

The 3941 is unreliable with NAT - connections will randomly die.  The symptoms are things like web browsers seeming to hang / time out, etc.  It won't be everyone in the office at once, nor will it be predictable.

I've documented this in the IPv6 forum.

jaroop
Visitor

Re: Connection drops for a few seconds intermittently

Is there any modem Comcast offers that has no issues? I would love to just purchase my own and do my own routing to boot, but Comcast won't allow it with a static IP..

sgermain06
New Member

Re: Connection drops for a few seconds intermittently

I'm having this problem too.

 

Here's my setup: I have a 5 static IPs on this connection. I have 4 servers and a router for the rest of my network.

 

I can start a ping on my static IP gateway and get about 40% packet loss. I tried running this ping from my workstation (through my router), from one of my servers (directly connected to the modem) and from my router (also connected directly to my modem). They all show the same behavior and they all start dropping packets at the same time.

 

Here's another interesting issue: whenever I try to connect to my modem's web interface (10.1.10.1), whenever I see packet loss, the modem's web interface also stops responding. I tried changing the cable between my modem and my router, same problem. I tried connecting my laptop directly to the modem and I still get the same problem.

 

I can ping anything within my local network and I have no problem. I can also ping my server's external IP addresses and have no problem either.

 

Now, I know that before I upgraded my internet connection, we had a 50mpbs connection with a Netgear modem. And when I logged in to the Netgear modem, the WAN address was a random IP address assigned from their DHCP. It was my understanding that any static IP routing was happening through a tunnel that was configured between the device and their network and everything was being tunneled through that IP, assigned by their DHCP server. Now, that Cisco modem is showing its WAN IP address to be my static IP's gateway. Maybe the modem has different capabilities, I don't know, but I never had any issue with the Netgear modem before.

 

Anyone else ever had an issue like that?

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