Community Forum

DNS Servers are Intermittently Unresponsive

Xfinity Forum Archive
About the archive project

Xfinity Forum Archive...

This is an archived section of the community.

Content in this area has been identified as outdated or irrelevant.

This change was done in an effort to make the forum easier to use and to keep only the most helpful and recent content active.

Post your questions in the Xfinity Community

Frequent Visitor

DNS Servers are Intermittently Unresponsive

THE SITUATION

1. Comcast's DNS servers become unresponsive at random intervals for anywhere between 5 and 40 minutes at a time.
2. The periods of unresponsiveness happen all day long, but are worst in the evenings between 5:00PM and 10:00PM then again after 12:00AM.
3. Websites and pings will not respond by name (DNS lookup fails), but will respond immediately when accessed directly by their IP addresses.
4. Streaming audio from online radio stations and downloads started when things are working are NOT interrupted when DNS becomes unresponsive.
5. My mom, also a Comcast internet subscriber, who lives over 2 miles away has the EXACT same problem.
6. I and my mom are well below the bandwidth cap.
7. It happens regardless of whether I am behind my router or connected directly to the cable modem.
8. Resetting the modem will sometimes fix things for about 5 minutes or so before the problem comes back (probably just a coincidence).
9. A technician has been to my house and pronounced my equipment and signals to be in good working order.
10. If I start a ping just before the DNS becomes unresponsive, the ping will continue to work after the DNS stops responding since it already has the IP address.
11. VPN connections established before the DNS becomes unresponsive continue to work and I can access any internet address via my employer's DNS servers through the VPN tunnel.

This exact same problem first manifested itself about three years ago after many years of perfect service through @Home, AT&T Broadband and finally Comcast.  A Comcast-side equipment bandwidth upgrade fixed the problem, and all was perfect again until about 8 months ago.

The problem has been getting progressively worse since then.  Now, my internet connection is effectively dead for 90% of the evening hours and is unreliable for about 40% of the time during the day.

Comcast tech support has been utterly useless: they have cut me off during our phone conversations by resetting my modem without warning (I have Comcast voice too...), they have promised to elevate my issue and assured me I would get a call (it never came), they have sent a technician out who claims my connection is fine (it always works when they are here or when I call for help).

Even when the DNS is responsive, it has been taking longer and longer to provide IP addresses.  Web sites that used to come up instantly now take 30 seconds and up to a few minutes to fully display during brief windows of responsiveness during the trobulesome times.  If I go to a web site by using the IP address directly though, it will display instantly.  However, during the daytime, my connection is usually very fast: most web pages appear almost instantly and downloads are faster than ever.

I hope someone can help me.  I am an electrical engineer and am quite familiar with networking technology (I develop and support embedded ethernet products).  The situation described above and the data below convinces me that the problem is on Comcast's end, specifically with their DNS servers.  Please prove me wrong if you can.  It would be much easier if there is something I can fix myself than to continue fighting with the polite but ultimately useless phone support personnel.


THE DATA

MY CABLEMODEM

ARRIS DOCSIS 3.0 / PacketCable 1.5 Touchstone Telephony Modem
HW_REV: 7
VENDOR: Arris Interactive, L.L.C.
BOOTR: 1.2.1.20
SW_REV: 7.1.103
MODEL: TM702G


WHEN CONNECTION IS BAD

CABLE MODEM STATS

RF Parameters
Downstream
                DCID Freq          Power         SNR         Modulation    Octets       Correcteds Un
Downstream 1    1    693.00 MHz    -1.21 dBmV    36.17 dB    256QAM        944461383    248        0
Downstream 2    2    699.00 MHz    -1.34 dBmV    37.09 dB    256QAM        566036033    256        0
Downstream 3    3    705.00 MHz    -1.90 dBmV    36.84 dB    256QAM        513562806    252        0
Downstream 4    4    711.00 MHz    -2.15 dBmV    37.09 dB    256QAM        602094573    240        0

Upstream
              UCID Freq         Power         Channel Type         Symbol Rate    Modulation
Upstream 1    1    36.40 MHz    39.75 dBmV    DOCSIS2.0 (ATDMA)    5120 kSym/s    64QAM


--------------------------------------------------
PING TO COMCAST.NET
--------------------------------------------------
ping www.comcast.net
ping: unknown host www.comcast.net


--------------------------------------------------
PING TO GOOGLE.COM
--------------------------------------------------
ping www.google.com
ping: unknown host www.google.com


--------------------------------------------------
PING TO 209.85.225.99 (a Google server)
--------------------------------------------------
ping 209.85.225.99
PING 209.85.225.99 (209.85.225.99) 56(84) bytes of data.
64 bytes from 209.85.225.99: icmp_seq=1 ttl=53 time=23.3 ms
64 bytes from 209.85.225.99: icmp_seq=2 ttl=53 time=25.3 ms
64 bytes from 209.85.225.99: icmp_seq=3 ttl=53 time=25.1 ms
64 bytes from 209.85.225.99: icmp_seq=4 ttl=53 time=25.6 ms
64 bytes from 209.85.225.99: icmp_seq=5 ttl=53 time=29.2 ms
64 bytes from 209.85.225.99: icmp_seq=6 ttl=53 time=24.0 ms
64 bytes from 209.85.225.99: icmp_seq=7 ttl=53 time=25.7 ms
7 packets transmitted, 7 received, 0% packet loss, time 6007ms
rtt min/avg/max/mdev = 23.358/25.495/29.210/1.716 ms


--------------------------------------------------
TRACEROUTE TO GOOGLE.COM

(Note: I use Linux.  traceroute -I is the equivalent of tracert on Windows)
--------------------------------------------------
traceroute -I www.google.com
www.google.com: Name or service not known


--------------------------------------------------
TRACEROUTE TO 209.85.225.99 (a Google server)
--------------------------------------------------
traceroute -I 209.85.225.99
traceroute to 209.85.225.99 (209.85.225.99), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  2.859 ms  3.869 ms  4.793 ms
 2  71.57.50.1 (71.57.50.1)  31.396 ms * *
 3  68.86.117.241 (68.86.117.241)  31.825 ms * *
 4  * * *
 5  * * *
 6  * * *
 7  * * *
 8  72.14.236.178 (72.14.236.178)  23.978 ms  24.798 ms  25.265 ms
 9  * * 72.14.232.141 (72.14.232.141)  36.106 ms
10  209.85.241.35 (209.85.241.35)  34.668 ms  37.695 ms 209.85.241.37 (209.85.241.37)  44.943 ms
11  72.14.239.18 (72.14.239.18)  44.167 ms  44.499 ms 209.85.248.106 (209.85.248.106)  38.890 ms
12  209.85.225.99 (209.85.225.99)  36.478 ms  37.307 ms  39.532 ms


--------------------------------------------------
TRACEROUTE TO 75.75.75.75 (Comcast Primary DNS)
--------------------------------------------------
traceroute -I 75.75.75.75
traceroute to 75.75.75.75 (75.75.75.75), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  1.343 ms  2.342 ms  3.264 ms
 2  71.57.50.1 (71.57.50.1)  19.012 ms * *
 3  * * *
 4  68.87.231.69 (68.87.231.69)  20.652 ms * *
 5  * * *
 6  * * *
 7  * * 75.75.75.75 (75.75.75.75)  15.963 ms


--------------------------------------------------
TRACEROUTE TO 184.51.206.8 (COMCAST.NET)
--------------------------------------------------
traceroute -I 184.51.206.8
traceroute to 184.51.206.8 (184.51.206.8), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  1.405 ms  2.343 ms  3.373 ms
 2  71.57.50.1 (71.57.50.1)  18.136 ms * *
 3  68.86.117.241 (68.86.117.241)  20.016 ms * *
 4  * * *
 5  * * *
 6  * * *
 7  * * 184.51.206.8 (184.51.206.8)  16.927 ms
(note that only IP addresses are displayed - when connection works, domain names are shown with the IP in parentheses)


--------------------------------------------------
TRACEROUTE TO 184.51.206.42 (COMCAST.NET)
--------------------------------------------------
traceroute -I 184.51.206.42
traceroute to 184.51.206.42 (184.51.206.42), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  1.316 ms  2.258 ms  3.226 ms
 2  71.57.50.1 (71.57.50.1)  20.147 ms * *
 3  68.86.117.241 (68.86.117.241)  21.916 ms * *
 4  * * *
 5  * * *
 6  * * *
 7  * * a184-51-206-42.deploy.akamaitechnologies.com (184.51.206.42)  14.074 ms
(DNS started responding at end of traceroute)



WHEN CONNECTION IS GOOD

CABLE MODEM STATS

RF Parameters
Downstream
                DCID Freq          Power         SNR         Modulation    Octets       Correcteds Un
Downstream 1    1    693.00 MHz    -1.61 dBmV    36.17 dB    256QAM        535632602    195        0
Downstream 2    2    699.00 MHz    -1.59 dBmV    37.09 dB    256QAM        306932230    205        0
Downstream 3    3    705.00 MHz    -2.18 dBmV    36.84 dB    256QAM        253104511    199        0
Downstream 4    4    711.00 MHz    -2.45 dBmV    37.09 dB    256QAM        330585914    195        0

Upstream
              UCID Freq         Power         Channel Type         Symbol Rate    Modulation
Upstream 1    1    36.40 MHz    39.75 dBmV    DOCSIS2.0 (ATDMA)    5120 kSym/s    64QAM


--------------------------------------------------
PING TO GOOGLE.COM
--------------------------------------------------
ping google.com
PING google.com (74.125.225.19) 56(84) bytes of data.
64 bytes from 74.125.225.19: icmp_seq=1 ttl=55 time=12.7 ms
64 bytes from 74.125.225.19: icmp_seq=2 ttl=55 time=16.1 ms
64 bytes from 74.125.225.19: icmp_seq=3 ttl=55 time=17.5 ms
64 bytes from 74.125.225.19: icmp_seq=4 ttl=55 time=12.7 ms
64 bytes from 74.125.225.19: icmp_seq=5 ttl=55 time=15.3 ms
64 bytes from 74.125.225.19: icmp_seq=6 ttl=55 time=83.9 ms
64 bytes from 74.125.225.19: icmp_seq=7 ttl=55 time=12.9 ms
7 packets transmitted, 7 received, 0% packet loss, time 41460ms
rtt min/avg/max/mdev = 12.736/24.491/83.922/24.324 ms


--------------------------------------------------
PING TO COMCAST.NET
--------------------------------------------------
ping www.comcast.net
PING a1526.g.akamai.net (198.63.194.72) 56(84) bytes of data.
64 bytes from 198.63.194.72: icmp_seq=1 ttl=55 time=23.4 ms
64 bytes from 198.63.194.72: icmp_seq=2 ttl=55 time=19.8 ms
64 bytes from 198.63.194.72: icmp_seq=3 ttl=55 time=21.5 ms
64 bytes from 198.63.194.72: icmp_seq=4 ttl=55 time=16.2 ms
64 bytes from 198.63.194.72: icmp_seq=5 ttl=55 time=18.3 ms
64 bytes from 198.63.194.72: icmp_seq=6 ttl=55 time=19.6 ms
64 bytes from 198.63.194.72: icmp_seq=7 ttl=55 time=30.5 ms
7 packets transmitted, 7 received, 0% packet loss, time 60540ms
rtt min/avg/max/mdev = 16.238/21.394/30.567/4.301 ms

--------------------------------------------------
PING TO COMCAST PRIMARY DNS @ 75.75.75.75
--------------------------------------------------
ping 75.75.75.75
PING 75.75.75.75 (75.75.75.75) 56(84) bytes of data.
64 bytes from 75.75.75.75: icmp_seq=1 ttl=59 time=12.3 ms
64 bytes from 75.75.75.75: icmp_seq=2 ttl=59 time=11.2 ms
64 bytes from 75.75.75.75: icmp_seq=3 ttl=59 time=13.7 ms
64 bytes from 75.75.75.75: icmp_seq=4 ttl=59 time=14.8 ms
64 bytes from 75.75.75.75: icmp_seq=5 ttl=59 time=12.3 ms
64 bytes from 75.75.75.75: icmp_seq=6 ttl=59 time=12.7 ms
6 packets transmitted, 6 received, 0% packet loss, time 5006ms
rtt min/avg/max/mdev = 11.280/12.904/14.886/1.151 ms


--------------------------------------------------
TRACEROUTE TO COMCAST.NET
--------------------------------------------------
traceroute -I www.comcast.net
traceroute to www.comcast.net (184.51.206.8), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  2.942 ms  3.983 ms  5.004 ms
 2  71.57.50.1 (71.57.50.1)  21.020 ms * *
 3  te-6-4-ur08.mtprospect.il.chicago.comcast.net (68.86.117.241)  22.485 ms * *
 4  * * *
 5  * * *
 6  * * *
 7  * a184-51-206-8.deploy.akamaitechnologies.com (184.51.206.8)  14.063 ms  16.318 ms


--------------------------------------------------
TRACEROUTE TO GOOGLE.COM
--------------------------------------------------
traceroute -I www.google.com
traceroute to www.google.com (74.125.225.18), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  1.367 ms  2.465 ms  3.512 ms
 2  71.57.50.1 (71.57.50.1)  20.496 ms * *
 3  te-6-4-ur08.mtprospect.il.chicago.comcast.net (68.86.117.241)  20.774 ms * *
 4  * * *
 5  * * *
 6  * * *
 7  * 66.208.228.202 (66.208.228.202)  14.582 ms  13.696 ms
 8  * * *
 9  * * *
10  * * *
11  * * *
12  * * 74.125.225.18 (74.125.225.18)  15.785 ms

--------------------------------------------------
TRACEROUTE TO COMCAST PRIMARY DNS @ 75.75.75.75
--------------------------------------------------
traceroute -I 75.75.75.75
traceroute to 75.75.75.75 (75.75.75.75), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  1.387 ms  2.303 ms  3.272 ms
 2  71.57.50.1 (71.57.50.1)  17.975 ms * *
 3  te-6-4-ur08.mtprospect.il.chicago.comcast.net (68.86.117.241)  19.791 ms * *
 4  po-10-ur07.mtprospect.il.chicago.comcast.net (68.87.231.69)  17.544 ms * *
 5  * * *
 6  * * *
 7  * * cdns01.comcast.net (75.75.75.75)  40.577 ms


--------------------------------------------------
TRACEROUTE TO 184.51.206.42 (COMCAST.NET)
--------------------------------------------------
traceroute -I  184.51.206.42
traceroute to 184.51.206.42 (184.51.206.42), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  1.211 ms  2.137 ms  3.039 ms
 2  71.57.50.1 (71.57.50.1)  18.978 ms * *
 3  te-6-4-ur08.mtprospect.il.chicago.comcast.net (68.86.117.241)  20.640 ms * *
 4  * * *
 5  * * *
 6  * * *
 7  * a184-51-206-42.deploy.akamaitechnologies.com (184.51.206.42)  13.642 ms  13.560 ms







Expert

Re: DNS Servers are Intermittently Unresponsive

The forum administrator here will be made aware of your issue for a potential escalation.



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

Thanks.  I look forward to hearing from them.

 

I just had another DNS "outage" starting at 1:28PM CDT and lasting about 4 minutes.  During that time I was able to work normally through a VPN connection I established on my laptop eariler this morning, but the problems described above were there for my desktop which was not communicating via VPN.

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

Might this have something to do with the phasing out of the Domain Helper servers? (I use the opt-out/DNSSEC servers)  I found this on the DNSSEC FAQ:

We are trialing DNSSEC to see how it scales on production DNS servers under load, preparing our production network for DNSSEC and any associated processes needed to troubleshoot any potential DNSSEC-related technical errors which may occur.

 

If it does, I can say with a fairly high degree of certainty that DNSSEC doesn't scale well under load. Smiley Happy

 

I have found over a dozen other posts from the last month alone describing problems just like mine, all without any resolution which would suggest that this is a widespread problem (many of the posts were also from the Chicago area). 

Others may not realize what the likely source of the problem really is.  My mother for example thought it was just that the web sites she was trying to reach were down or no longer active so she didn't bother to complain.  Tests I have run on her machine revealed the same problems I have been experiencing.  I wonder how many other non-technical customers are experiencing the same problems, but don't have the knowledge to do their own troubleshooting or to accurately describe the problem to Comcast tech support personnel?

Expert

Re: DNS Servers are Intermittently Unresponsive

In the interim try using alternate third party DNS servers such as the OpenDNS or the Google offerings. 



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

Thanks.  I've tried third party DNS servers, and they work well if my PC is connected directly to the cable modem.  Unfortunately, my router's feature for using alternate DNS servers doesn't work well and it defaults to the Comcast assigned DNS no matter what I put in (known issue with my router).  Based on the setup of my home network, directly connecting to the cable modem for anything but an occasional test is impractical.

 

Until my router's manufacturer releases a patch (not likely for this model router), I'm stuck with Comcast's DNS servers unless I buy a new router.  Hopefully, someday I'll get what I'm paying for from Comcast since their DNS servers are much faster for me - when they are working.

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

I also just noticed that even though I am using the opt-out server (as my account settings will attest to), I am still experiencing domain hijacking by the Domain Helper.  When I go to www.example.com, I get a Comcast page with friendly suggestions rather than the correct site which is a redirect to the iana.org page explaining what example.com is and how it is reserved for documentation.  So there is definitely something fishy going on with Comcast's DNS servers...

 

Expert

Re: DNS Servers are Intermittently Unresponsive

If your current config is pointing to the anycast DNSSec servers at 75.75.75.75 or 75.75.76.76 then that can't happen as their Domain Helper service is not enabled/used on those servers.



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Diamond Problem Solver

Re: DNS Servers are Intermittently Unresponsive

I just have to jump in here and share that I am also in the NW suburbs, and have not changed the default domain helper settings in my account.  I pickup the normal Chicago region DNS servers at 68.87.72.134 and 68.87.77.134.  I have none of the DNS issues that the OP has, so I am wondering what is different on his setup that no one else in the region is seeing.  If this was even remotely widespread, there would be many posters here complaining here or on BBR.

 

I am a default kind of guy, and don't modify anything unless necessary, and don't have any DNS issues.

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

EG, my router is absolutely pointing to 75.75.75.75 / 75.75.76.76 for DNS.  Impossible or not, it IS happening.  Something is very wrong.  Every test I can think of shows 75.75.75.75 being used.  And for the record, all my machines are set to use the DNS provided by my router (full DHCP rather than DHCP Address Only).

 

I may try the opt-in/default servers as suggested by JaylnAlg and see if that fixes things, but I seem to remember them being no better when I switched several months ago.  However, customers are being migrated away from those and by the end of the month, everyone will be on a DNSSEC server like 75.75.75.75.

 

I wouldn't be surprised if the DNSSEC server in particular was the source of the problem, but since everyone will be using them shortly, Comcast should be aware of the issues.

 

Edited to add: I just ran Wireshark and can confirm that I am using 75.75.75.75.  However, I am no longer getting hijacked and I have made no changes whatsoever.  It is almost as if someone at Comcast is watching and tweaking things, because I have had almost no outages this evening.  Every night for the last couple of months between 5PM and 10PM I have essentially had no internet connection except for brief windows that popped up randomly.  Tonight, things are perfect (so far).

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

Up until 10:00, this was the best night for connectivity in over a year.  Everything was fast.  Then at 10:00, I had another DNS server connection problem that lasted until 10:04.  I'll add updates to this post if I get more...

Expert

Re: DNS Servers are Intermittently Unresponsive


@k9xf wrote:

Up until 10:00, this was the best night for connectivity in over a year.  Everything was fast.  Then at 10:00, I had another DNS server connection problem that lasted until 10:04. 

 

 

How do you know this was a DNS issue exactly ? Got at least a trace to that server at that moment ?



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

The same way I determined that it was a DNS issue illustrated above.  I did pings and traceroutes on both domain names (failed) and IP addresses (succeeded).  The results were the same as above, but because timing numbers didn't vary appreciably, I didn't bother to save them.  I verified that my VPN connection to my corporate server was still active on my laptop (it was).

On one of my computers, I keep open two terminal windows, a web browser with pages open to the cable modem and my router, and sometimes wireshark so that I can troubleshoot these random outages as they occur.  If you feel it is necessary for me to capture the data every time I have one of these outages to add to the compilation above, I can certainly do so.  I just don't think it will add anything since the behavior is the same as I have already described above.

Expert

Re: DNS Servers are Intermittently Unresponsive

Well if 'you' feel that enough data has been posted here then anything more is futile I guess. As I've stated, the forum admin has been notified...



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

As I said, I'd be happy to post more data if you want it.  I was just explaining why I didn't post it in the first place - I didn't think more of the same would help since the data was essentially identical to what I provided in my first post.  I guess I'm wrong.  No need to be snarky.  I'll happily fill this thread with the text output of pings and traceroutes and signal strenth with every outage.

 

However, I did feel that posting the times of any recent outages I experienced might be valuable to the admin in case they can get someone to look at the server logs and check out the load and other relevant data for those times.  If the server reports nothing out of the ordinary, then perhaps it isn't the DNS server after all, but rather something between me and the server.  Or, if there is something out of the ordinary, they would now have a hint as to what the problem might be.  Or maybe its useless, in which case they can simply discard it, but I've seen it asked for in other posts complaining about similar problems.

 

Is there any other information I've missed that you feel might help?  I'm open to suggestions.

Retired Administrator
Moved:

Re: DNS Servers are Intermittently Unresponsive

Retired Administrator

Re: DNS Servers are Intermittently Unresponsive

 


@k9xf wrote:

As I said, I'd be happy to post more data if you want it.  I was just explaining why I didn't post it in the first place - I didn't think more of the same would help since the data was essentially identical to what I provided in my first post.  I guess I'm wrong.  No need to be snarky.  I'll happily fill this thread with the text output of pings and traceroutes and signal strenth with every outage.

 

However, I did feel that posting the times of any recent outages I experienced might be valuable to the admin in case they can get someone to look at the server logs and check out the load and other relevant data for those times.  If the server reports nothing out of the ordinary, then perhaps it isn't the DNS server after all, but rather something between me and the server.  Or, if there is something out of the ordinary, they would now have a hint as to what the problem might be.  Or maybe its useless, in which case they can simply discard it, but I've seen it asked for in other posts complaining about similar problems.

 

Is there any other information I've missed that you feel might help?  I'm open to suggestions.


Are you able to post a tracert without the router when you experience the problem?

 

Just 'Dete'
Retired Help Forums Admin



Community Icon
I am a Retired Official Comcast Employee, and I no longer actively support the forum.
Official Employees are from multiple teams within Comcast: Product, Support, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.

Was your question answered? Mark it as an accepted solution!solution Icon
Community Icon
I am an Retired Official Comcast Employee.
Official Employees are from multiple teams within Comcast.
We ask that you post publicly so people with similar questions may benefit.
Was your question answered? Mark it as an accepted solution!solution Icon
Community Icon
Retired Comcast Employee.
Please post so people with similar questions may benefit.
Was your question answered?
Mark it as a solution!solution Icon

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

Yes, I'll do that during the next DNS "outage" (for lack of a better term).  Of course, shortly after I created this thread, my connection has suddenly improved dramatically - two nights of virtually uninterrupted surfing for the first time in 8 months.  I have made no changes to anything on my end whatsoever.  It is almost as if someone at Comcast saw this and flipped a switch.  Smiley Wink

 

I have a laptop next to my cablemodem and router ready to go as soon as the problem manifests itself again.  All I need to do is swap a cable.

 

Thank you very much for getting involved.  I really appreciate it.

Retired Administrator

Re: DNS Servers are Intermittently Unresponsive

 


@k9xf wrote:

Yes, I'll do that during the next DNS "outage" (for lack of a better term).  Of course, shortly after I created this thread, my connection has suddenly improved dramatically - two nights of virtually uninterrupted surfing for the first time in 8 months.  I have made no changes to anything on my end whatsoever.  It is almost as if someone at Comcast saw this and flipped a switch.  Smiley Wink

 

I have a laptop next to my cablemodem and router ready to go as soon as the problem manifests itself again.  All I need to do is swap a cable.

 

Thank you very much for getting involved.  I really appreciate it.


Happy to help - let us know!

 

Just 'Dete'
Retired Help Forums Admin



Community Icon
I am a Retired Official Comcast Employee, and I no longer actively support the forum.
Official Employees are from multiple teams within Comcast: Product, Support, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.

Was your question answered? Mark it as an accepted solution!solution Icon
Community Icon
I am an Retired Official Comcast Employee.
Official Employees are from multiple teams within Comcast.
We ask that you post publicly so people with similar questions may benefit.
Was your question answered? Mark it as an accepted solution!solution Icon
Community Icon
Retired Comcast Employee.
Please post so people with similar questions may benefit.
Was your question answered?
Mark it as a solution!solution Icon

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

Well, the problem is back.  The outages don't seem to last as long and are not quite as frequent.  I'm trying to get a traceroute while directly connected to the cable modem, but every time it has happened so far, I haven't been fast enough and DNS starts working again as soon as I make the switch.  When I switch back from the direct connection, everything works again through my router.

 

I have come up with a workaround (a very easy one for Linux users) that also works around my router's bug where it won't use a custom DNS server address.  On one PC I have created a local DNS cache.   Lookups go to the local cache first, then the cache software will go to Comcast if the cache has no entry and finally to Google's DNS if Comcast fails.   So far, I have experienced no symptoms of the outages on this particular PC, while my other PCs are still plagued with them.

 

Based on this evidence, what other possibilities are there other than faulty DNS servers on Comcast's end?  I'm open to suggestions.

Silver Problem Solver

Re: DNS Servers are Intermittently Unresponsive

You can go into C:\Windows\System32\drivers\etc>  and edit the Hosts file to provide static DNS entries  for your most used sites.  (Faster than DNS lookup)

 

If you want to Google it, use "Windows Hosts" to narrow it down.

 

Frequent Visitor

Re: DNS Servers are Intermittently Unresponsive

I've done that before with my Linux machines (/etc/hosts file).  However, that has serious limitations.  Most web sites today have dozens of links to ads and other services that require the resolution of many addresses before the page will even begin to display something remotely readable.  A local DNS cache is far more flexible and just as fast as using the hosts file.  The cache will not only store my most frequenly visited web sites, but it will also remember all those additional links that are needed.  Plus, it will resort to a traditional lookup from Comcast's (or any open) DNS servers if no local entry is found.

Silver Problem Solver

Re: DNS Servers are Intermittently Unresponsive

Sounds like you have it pretty well worked out.

Please post back and let uw know how it works out for you.

Regular Visitor

Re: DNS Servers are Intermittently Unresponsive

I can confirm this happening in Portland. Although I am here looking for info on the second compete outage today (firewall looses connection, can't get a dhcp address even though modem is up) the dns server outages started happening earlier this week. Since I run my own dhcp and dns relay, I added verizon 4.2.2.1 dns servers as secondaries. I also got the hijack page even though I've opted out multiple times.






Problem Solver

Re: DNS Servers are Intermittently Unresponsive

I'm seeing this too in Chicago. The Comcast servers at 75.75.75.75 and 75.75.76.76 will stop responding for perhaps 30 seconds, then start working again. Packet captures typically show two requests to each server with no response. That will happen several times for around 30 seconds, then everything starts working again. Occasionally things get weird and I'll see a bunch of "Server failure" responses from server addresses to which I never sent a query:

 

                    68.87.72.141

                    68.87.72.142

                    68.87.72.133

                    68.87.72.137

 

Those addresses seem awfully familiar.

 

Thankfully, I'm blissfully unaware of most of this unless I look at the firewall logs for DNS traffic to/from addresses other than my assigned Comcast name servers. I'm running BIND in a "forward first" configuration. If the assigned upstream servers don't work, it just does the lookup itself.

New Poster

Re: DNS Servers are Intermittently Unresponsive

Comcast will have to fix the DNS wierdness, but I might have a better work-around to use in the meantime.  

 

You said that limitations in your router prevent you from using alternate DNS server IP's (OpenDNS or Google) in your home network.  You have also found a manual (computer by computer) way to work around this.

 

Here's another temporary fix.  You don't have to use your router as the DHCP server for your network.  You can turn that function off in the router, and use one of your computers to provide DHCP - over which you will have much more fine grain control.  That includes the ability to set DNS servers for all your network clients to point wherever you choose.  (I am not explaining all these services because it sounds like you know your way around networking.  If I am not assuming correctly, please call me on that and I will

spell it out in more detail.)

 

You can make one of your Linux computers a DHCP server.  That is available in most Linix distros (though it can take some fiddeling to get it configured). Windows XP has the DHCP service hidden away, though it can be revealed with a registry hack.  Windows 7 and Vista do not include a DHCP server service, but there are DHCP services for Windows that you can download.  Here are a few:

 

 

 

Again, this doesn't solve the problem, (Only Comcast can do that.) But at least it will shield your home network from it's effects.

 

 

 

 

 

 

Silver Problem Solver

Re: DNS Servers are Intermittently Unresponsive

Nice post.  Thanks for the Info and Links

 

New Poster

Re: DNS Servers are Intermittently Unresponsive

I had these exact same problems in January.  I would switch to Google's servers when the problems happened.  The next day or so I would change back to Comcast servers.  Eventually I'd run into an "outage" again and flip back to Google.  

 

It would be nice to use the Comcast servers (e.g. to avoid known issues with Akamai mapping when using Google's servers), but they have just not been reliable enough.

 

I've been using Google's servers for a few months with not a single problem.  I'll switch back to Comcast again and see if the problems persist.

 

 

New Poster

Re: DNS Servers are Intermittently Unresponsive

I also live in West Chicago and had the same long-term, random DNS outages as described by the OP and others here. Went through the typical Comcast three-ring circus of customer service: (Ring 1 - know-nothing minimum wage phone techs; Ring 2 - useless equipment replacements; Ring 3 - combat fatigue and acceptance of inferior service at high prices).

 

Since the massive DNS outages here and in Boston, I can't open more than one tab at a time without getting a DNS error. Usually if I reload the page five or six times it will eventually 'catch' and load. Sometimes they load only portions of the data, and the page appears old-school BBS style with no graphics or formatting, especially sites like youtube, twitter, or wikipedia.

 

I don't expect any real resolution to this problem from Comcast, but at least I got to throw my voice into the mix.

 

New Poster

Re: DNS Servers are Intermittently Unresponsive

Just for kicks, I also switched my router and adapter to Google DNS (My laptop is on auto since it travels a lot).  Problem solved. Pages open fast and I can keep opening them rapid fire with no DNS failures. It's pretty solidly confirmed in my mind - Comcast's DNS servers are the problem.

 

Regular Contributor

Re: DNS Servers are Intermittently Unresponsive

I am having similar troubles outside the Chicago area. Everything has been good for years, and just went to  potatoes.

 

Tried using OpenDNS myself, no help. Just no throughput. Upload normal at 4mbs.

 

Modem is changing frequencies, something it never did.

New Poster

Re: DNS Servers are Intermittently Unresponsive


@theelviscerator wrote:

I am having similar troubles outside the Chicago area. Everything has been good for years, and just went to  potatoes.

 

Tried using OpenDNS myself, no help. Just no throughput. Upload normal at 4mbs.

 

Modem is changing frequencies, something it never did.


I used google dns specifically, not OpenDNS. My D/L seems normal (by comcast standards) at about 3-6 mbps during primetime now. Make sure when you switch to Google you set IPv6 and IPv4, both options

Expert

Re: DNS Servers are Intermittently Unresponsive

DNS has nothing to do with actual throughput/transfer rate..



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
New Poster

Re: DNS Servers are Intermittently Unresponsive


@EG wrote:

DNS has nothing to do with actual throughput/transfer rate..



And I saw no change in my transfer, but I have had no service interruptions or bad DNS errors since I changed.

Regular Contributor

Re: DNS Servers are Intermittently Unresponsive

I realize that name servers have nothing to do with throughput, but web pages refusing to load is causing my drop in dl speed.

Expert

Re: DNS Servers are Intermittently Unresponsive

I understand what you are saying, but that's not technically correct. DNS deficiencies can cause delays in webpage loading (especially complex ones)/perception but that has nothing to do with a "drop" in actual download speed/througput with file transfers.



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
New Poster

Re: DNS Servers are Intermittently Unresponsive

same problem here.  unacceptable.  we pay way too much to comcast each month for there to be these issues.   DNS server is intermittently unresponsive.  we are located in richmond tx 77407.  problem started here within the last month but in the last week happens every day.  no help or solutions from comcast.