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Problem with Comcast Node -- 30% Packet Loss

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Frequent Visitor

Problem with Comcast Node -- 30% Packet Loss

I have been having a steadily worsening problem with my Comcast Node in Center City Philadelphia.  It used to be on occasion in the 6-8 PM time frame that I would experience sporadic, high packet loss.  Now, it seems to be worsening and occurs most of the day and most days.  By running a ping -t for an extended period of time, I will receive 15-20% packet loss to the FIRST node from my cable modem (found as first hop through a tracert to www.google.com).  Periodically there will be no packet loss and the internet will be solid/fast/no issues, but usually several times every 10-15  minutes, the packet loss will start and the internet becomes unusable -- no ability to go to basic web pages, no streaming, etc, etc.

 

I have had a technician out already who fixed my signal issues.  The signals on the modem are now within range as I understand it and can see on the modem status pages.  But within minutes after the technician has left, the intermittent packet loss started again.  I have called Comcast multiple times, have another technician coming tomorrow, have reset the modem, reset the router, plugged directly into the cable modem, etc, etc.  Furthermore, the last technician traced the coaxial wire from the Comcast box on the street (right beside my doorstep) into my house (approximately 20 feet of coaxial cable run, directly into the cable modem, no odd/weird setup).  

 

Given that it appears to be worsening, from my reading it appears to be a Comcast signal problem.  I'm wondering how to get this escalated so that it can be investigated and addressed.  I have spoken to my neighbors and they claim to have the same problems, but they do not have the same level of ability to look into the problems that I do, so can't be sure they are experiencing the same problems, although they say they do.  Below are some pings from when the problem is happening:

 

Request timed out.
Reply from 96.120.78.113: bytes=32 time=891ms TTL=254
Reply from 96.120.78.113: bytes=32 time=12ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=265ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=636ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=1002ms TTL=254
Reply from 96.120.78.113: bytes=32 time=13ms TTL=254
Request timed out.
Reply from 96.120.78.113: bytes=32 time=1153ms TTL=254
Reply from 96.120.78.113: bytes=32 time=14ms TTL=254
Reply from 96.120.78.113: bytes=32 time=10ms TTL=254
Reply from 96.120.78.113: bytes=32 time=11ms TTL=254
Reply from 96.120.78.113: bytes=32 time=11ms TTL=254
Reply from 96.120.78.113: bytes=32 time=11ms TTL=254

Ping statistics for 96.120.78.113:
Packets: Sent = 304, Received = 209, Lost = 95 (31% loss),
Reply from 96.120.78.113: Approximate round trip times in milli-seconds:
Minimum = 9ms, Maximum = 3679ms, Average = 292ms

 

Can anyone help get this diagnosed/fixed???  Any help would be appreciated!

 

Accepted Solution

Re: Problem with Comcast Node -- 30% Packet Loss

I believe the QoS with bandwidth limits has fixed my problem.  This Bufferbloat issue appears to have been the culprit all along.  I no longer have the high packet loss and the internet works as expected, for the first time in a long time!  I'm calling this done for now!

View answer in context
Frequent Visitor

Comcast Node Issue - >50% Packet Loss!

I have had numerous calls in to 1-800-Comcast and have had numerous technicians visit (3rd one coming in 2 days) and I wanted to see if someone could help me escalate my issue.

 

My neighbors and I have had steadily worsening intermittent packet loss.  Over the past two years it started off infrequently (usually in the 6-8 PM time frame), maybe a day/week, but is now to the point where it is multiple times per hour, for most of the day.  I have done all the usual things of rebooting the cable modem, technician has checked signal strength, traced wire from comcast connection to house (from a Comcast box 20 feet directly to cable modem, simple), connected directly to cable modem, etc, etc.  It is not an issue with my cable modem nor setup, as it is also happening to my neighbors to the point where Comcast is not usable.

 

I did a tracert to www.google.com and found the first hop outside my router is a Comcast (assume) node at 96.120.78.113.  By ping -t that address for an extended period of time, it shows massive packet loss (58% as can be seen below).  Can someone please help us escalate to have the node/upstream looked at?

 

Reply from 96.120.78.113: bytes=32 time=899ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=1300ms TTL=254
Reply from 96.120.78.113: bytes=32 time=35ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=640ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=1057ms TTL=254
Reply from 96.120.78.113: bytes=32 time=10ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=459ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=767ms TTL=254

Ping statistics for 96.120.78.113:
Packets: Sent = 51, Received = 21, Lost = 30 (58% loss),
Approximate round trip times in milli-seconds:
Minimum = 10ms, Maximum = 1300ms, Average = 512ms

 

It is intermittent, sometimes it will work, sometimes it will get the packet loss (typically in the evenings, but now almost constantly, even during the middle of the day).  Streaming internet TV, skype, speedtest fails (connection issues), and even just going to google.com do not work when the packets are being lost.  And then it gets better and our speedtest shows full speed and we see no packet loss.

 

This is something on Comcast's end, and I just need someone at Comcast to fix their gear.  Can someone help me get this escalated to expert tech support?

Frequent Visitor

Re: Comcast Node Issue - >50% Packet Loss!

The saga continues, but I had an idea.  I left ping on overnight (1 hop away to the comcast node/router/whatever) and into the next day, almost 24 hours.  Rock solid from the morning throughout the day, but come the evening, massive packet loss.  See the *64242* pings sent.  

 

Ping statistics for 96.120.78.113:
Packets: Sent = 64242, Received = 59865, Lost = 4377 (6% loss),
Approximate round trip times in milli-seconds:
Minimum = 6ms, Maximum = 3995ms, Average = 74ms

 

Only 6% loss (because it was good all day), but when it's bad, it's BAD.  Here's a small ping from the evening when my issues began again (from around 5 PM to the wee hours of the day is when it's bad)

 

Reply from 96.120.78.113: bytes=32 time=794ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=1072ms TTL=254
Reply from 96.120.78.113: bytes=32 time=11ms TTL=254
Reply from 96.120.78.113: bytes=32 time=1233ms TTL=254
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=319ms TTL=254
Request timed out.
Request timed out.
Reply from 96.120.78.113: bytes=32 time=1174ms TTL=254
Reply from 96.120.78.113: bytes=32 time=10ms TTL=254
Request timed out.

Ping statistics for 96.120.78.113:
Packets: Sent = 21, Received = 8, Lost = 13 (61% loss),
Approximate round trip times in milli-seconds:
Minimum = 10ms, Maximum = 1233ms, Average = 597ms

 

Average over 1/2 a second for a ping!  Internet = unusable.  I think I've got this narrowed down, tech is coming tomorrow at 3 PM (hope it's acting up by then).  If so, maybe I'll get some support.  But I'll post back either way.

Cable Expert
Moved:

Re: Comcast Node Issue - >50% Packet Loss!

Cable Expert

Re: Problem with Comcast Node -- 30% Packet Loss

You should...

  • Run a test to an IP address on the Internet, such as a web server, email server or other computer that should have high-availability and accepts ICMP traffic.
  • Run a test to a local IP address on your network such as a router or another computer, that accepts ICMP traffic to determine local network connectivity.
  • Run a test to your modem/gateway's local IP address, such as 192.168.100.1 or 10.0.0.1. This can help determine connectivity between your computer and your modem.
  • Run a test to 127.0.0.1 to ensure your network interface card is responding.

You shouldn't...

  • Run a test to a CMTS or node. The network interfaces in these pieces of equipment are designed to de-prioritize ICMP traffic and will provide false-positives. Our team has more accurate means to determine if there is a problem in your area.
  • Run a test to 75.75.75.75, 75.75.76.76 or other Comcast DNS server. These servers de-prioritize ICMP traffic and will provide false-positives of high latency or dropped packets.
  • Run a test to your modem/gateway's external IP address while on your network.
  • Run a test while connected to a VPN service. Due to their nature, VPN services create a false-positive rich environment and won't return accurate results.
  • Run a test while connected wirelessly, unless a comparison test has first be performed while directly connected to the modem/gateway.



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Frequent Visitor

Re: Problem with Comcast Node -- 30% Packet Loss

Hi Nerdbug.

Thank you for the info.

 

I did not run my tests using ICMP traffic but both TCP and UDP traffic.

Cable Expert

Re: Problem with Comcast Node -- 30% Packet Loss

@fotopfotop 

I've asked a Comcast employee to help you. You should expect a reply in this thread. 




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We ask that you post publicly so people with similar questions may benefit from the conversation.
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I am an XFINITY Forum Expert and I am here to help.
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Frequent Visitor

Re: Problem with Comcast Node -- 30% Packet Loss

Thanks for responding, I really appreciate it!  I've done most of what you said already, and now have done the rest...

 

You should...

  • Run a test to an IP address on the Internet, such as a web server, email server or other computer that should have high-availability and accepts ICMP traffic.  I started with ping -t to www.google.com and noticed the dropped packets.  Then I did a tracert to see where it's slowing down.  I found that it is slowing down on my first hop in the tracert, a comcast CISCO node.  I now always have both ping -t www.google.com and ping -t <comcast node> and they fail on packets in lock step when the issues start.  
  • Run a test to a local IP address on your network such as a router or another computer, that accepts ICMP traffic to determine local network connectivity.  No issue here.  I can ping my wife's computer with almost no latency.  Same with pinging other routers (in my network, 192.168.1.1, 192.168.1.50, 192.168.1.100), no latency.
  • Run a test to your modem/gateway's local IP address, such as 192.168.100.1 or 10.0.0.1. This can help determine connectivity between your computer and your modem.  No issue with pinging the modem on 192.168.100.1 (my modem), no latency.  I cannot get to 10.0.0.1...  I have never used that IP.  Could that be something, or is that a different modem?
  • Run a test to 127.0.0.1 to ensure your network interface card is responding.  No issue here, no latency.  FYI, I  have 3 computers that I use periodically and cell phones.  I've done pings from the routers as well and when the packets are being dropped, all devices do not work -- not a device issue.

You shouldn't...

  • Run a test to a CMTS or node. The network interfaces in these pieces of equipment are designed to de-prioritize ICMP traffic and will provide false-positives. Our team has more accurate means to determine if there is a problem in your area.  Great, but if I ping google/amazon/yahoo/etc, I get the same packet loss in lock step as pinging the node.  When the packet loss occurs, the internet stops working, cannot even bring up google webpage for the most part.
  • Run a test to 75.75.75.75, 75.75.76.76 or other Comcast DNS server. These servers de-prioritize ICMP traffic and will provide false-positives of high latency or dropped packets.  Ok, I do not do that, but understood.
  • Run a test to your modem/gateway's external IP address while on your network.  I think I understand that, I have not done that.
  • Run a test while connected to a VPN service. Due to their nature, VPN services create a false-positive rich environment and won't return accurate results.  Correct, I have no VPN
  • Run a test while connected wirelessly, unless a comparison test has first be performed while directly connected to the modem/gateway.  I have a hard line and have been doing both hard line and wireless tests.  I have pings from the router to the modem (the router admin function has a ping function) and they experience the packet loss as well.
So, apart from the 10.0.0.1 not responding, it is not my network (which I am sure of), and it has something to do with Comcast's services, likely beyond the modem.  It's not just ping -- I cannot stream video, I cannot surf the web, I cannot do anything, ping was just a tool to narrow down the problem.  Any other ideas?  Can a comcast person look at that Cisco router and see how it is performing?  I'm willing to wager that's the problem.
Official Employee

Re: Problem with Comcast Node -- 30% Packet Loss

Hello @fotopfotop. I'd be happy to run diagnostics for you in effort to troubleshoot your internet service issues. Please send me a private message and include your full name, service address, and account number so I can access your account and start with Node/ Plant/Modem diagnostics. 




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Frequent Visitor

Re: Problem with Comcast Node -- 30% Packet Loss

So the saga continued after the latest tech visit, then I think I resolved it...

 

Tech came out today and did some re-wiring within the house (and grounded the cable) around 3-4 PM today (usually before packet loss starts).  Didn't have issues before he came, and once he did the fixes speed was rock solid as well.  I did start having some issues towards the end of his visit, but a modem reboot and router reboot seemed to fix it.  Service was rock solid until late at night, then started the 50% packet loss again.

 

I started to wonder if it was the modem (SB6141), but then I stumbled upon this thing called "bufferbloat".  It seemed to make sense, as I originally thought the service was deteriorating compared to last year, but realized it only really got bad when I downloaded to a slower service -- bufferbloat.  Look it up on the web.  The fix is to go into your router configuration and use the bandwidth limiter or Quality of Service features to limit the bandwidth to at or just under your speed from Comcast (so no actual speed reduction).

 

I can turn on the QoS and the problem goes away.  I turn it off, and it's immediately back.  This is also why when I reboot the router and modem, it sometimes gets better for a few minutes (before the buffers get all jammed up or whatever).  And it's a bigger problem with fast hardware and "slower" speed, which I experience more now, because I downgraded my service.  I'm going to keep this on for a while, but I think this is the answer -- limit speeds to at or below Comcast upload and download on your router, and I'm fixed!  I'll report back if it stays solid the next few days.

Frequent Visitor

Re: Problem with Comcast Node -- 30% Packet Loss

I believe the QoS with bandwidth limits has fixed my problem.  This Bufferbloat issue appears to have been the culprit all along.  I no longer have the high packet loss and the internet works as expected, for the first time in a long time!  I'm calling this done for now!