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Comcast XFINITY → [DNS] DNS Server Not Working

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« Question about speed tier costs • Looking at buying - Speeds drop when I enter my area? »

graysonf
MVM
join:1999-07-16
Fort Lauderdale, FL

graysonf

MVM

2013-Mar-26 11:48 am

[DNS] DNS Server Not Working

DNS servers assigned by DHCP to me are 75.75.75.75 and 75.75.75.76.

However, 75.75.75.76 is not working. Is any one else seeing this?

[fred@iDEQscope ~]$ nslookup
> server 75.75.75.76
Default server: 75.75.75.76
Address: 75.75.75.76#53
> news.alt.net
;; connection timed out; no servers could be reached

> server 75.75.75.75
> Default server: 75.75.75.75
Address: 75.75.75.75#53
> news.alt.net
Server: 75.75.75.75
Address: 75.75.75.75#53

Non-authoritative answer:
Name: news.alt.net
Address: 208.90.168.18
>
actions · 2013-Mar-26 11:48 am ·

YukonHawk
join:2001-01-07
Patterson, NY
1 edit

YukonHawk

Member

2013-Mar-26 12:06 pm

disregard
actions · 2013-Mar-26 12:06 pm ·

jaynick
lit up
Premium Member
join:2001-02-06
Sterling Heights, MI

1 recommendation

jaynick to graysonf

Premium Member

2013-Mar-26 12:08 pm

to graysonf
Try 75.75.76.76
actions · 2013-Mar-26 12:08 pm ·

cp
Premium Member
join:2004-05-14
Wheaton, IL

cp to graysonf

Premium Member

2013-Mar-26 12:10 pm

to graysonf
what the heck?

[root@computer ~]# dig @75.75.75.75 google.com
 
; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6_3.6 <<>> @75.75.75.75 google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 37933
;; flags: qr rd ra; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
 
;; Query time: 16 msec
;; SERVER: 75.75.75.75#53(75.75.75.75)
;; WHEN: Tue Mar 26 16:08:43 2013
;; MSG SIZE  rcvd: 12
actions · 2013-Mar-26 12:10 pm ·

graysonf
MVM
join:1999-07-16
Fort Lauderdale, FL

graysonf to jaynick

MVM

2013-Mar-26 12:12 pm

to jaynick
That one is not assigned to me by DHCP. I am questioning the one that is and doesn't work.
actions · 2013-Mar-26 12:12 pm ·
graysonf

graysonf to cp

MVM

2013-Mar-26 12:14 pm

to cp
So, neither work for you?
actions · 2013-Mar-26 12:14 pm ·

cp
Premium Member
join:2004-05-14
Wheaton, IL

cp

Premium Member

2013-Mar-26 12:15 pm

It doesn't appear so.

75.75.75.75 is giving me a connection refused.
75.75.75.76 is timing out...

I'm not on a Comcast network atm...
actions · 2013-Mar-26 12:15 pm ·

bradyr
YCCD - Network Operations
Premium Member
join:2008-10-27
Sonora, CA
(Software) pfSense
Netgear CM1200
Ubiquiti UAP-AC-HD

bradyr

Premium Member

2013-Mar-26 12:46 pm

on comcast network:

ryan@skynet:~$ dig @75.75.75.75 google.com
 
; <<>> DiG 9.8.1-P1 <<>> @75.75.75.75 google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22577
;; flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 0, ADDITIONAL: 0
 
;; QUESTION SECTION:
;google.com.                    IN      A
 
;; ANSWER SECTION:
google.com.             139     IN      A       74.125.224.99
google.com.             139     IN      A       74.125.224.104
google.com.             139     IN      A       74.125.224.100
google.com.             139     IN      A       74.125.224.110
google.com.             139     IN      A       74.125.224.96
google.com.             139     IN      A       74.125.224.98
google.com.             139     IN      A       74.125.224.105
google.com.             139     IN      A       74.125.224.103
google.com.             139     IN      A       74.125.224.102
google.com.             139     IN      A       74.125.224.97
google.com.             139     IN      A       74.125.224.101
 
;; Query time: 25 msec
;; SERVER: 75.75.75.75#53(75.75.75.75)
;; WHEN: Tue Mar 26 09:42:51 2013
;; MSG SIZE  rcvd: 204
 
ryan@skynet:~$ dig @75.75.76.76 google.com
 
; <<>> DiG 9.8.1-P1 <<>> @75.75.76.76 google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53816
;; flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 0, ADDITIONAL: 0
 
;; QUESTION SECTION:
;google.com.                    IN      A
 
;; ANSWER SECTION:
google.com.             118     IN      A       74.125.224.102
google.com.             118     IN      A       74.125.224.110
google.com.             118     IN      A       74.125.224.99
google.com.             118     IN      A       74.125.224.100
google.com.             118     IN      A       74.125.224.104
google.com.             118     IN      A       74.125.224.97
google.com.             118     IN      A       74.125.224.96
google.com.             118     IN      A       74.125.224.105
google.com.             118     IN      A       74.125.224.101
google.com.             118     IN      A       74.125.224.103
google.com.             118     IN      A       74.125.224.98
 
;; Query time: 43 msec
;; SERVER: 75.75.76.76#53(75.75.76.76)
;; WHEN: Tue Mar 26 09:43:20 2013
;; MSG SIZE  rcvd: 204

not on comcast network:
 
ryan@ryan-imac:~$ dig @75.75.75.75 google.com
 
; <<>> DiG 9.8.3-P1 <<>> @75.75.75.75 google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 37483
;; flags: qr rd ra; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
 
;; Query time: 16 msec
;; SERVER: 75.75.75.75#53(75.75.75.75)
;; WHEN: Tue Mar 26 09:43:10 2013
;; MSG SIZE  rcvd: 12
 
ryan@ryan-imac:~$ dig @75.75.76.76 google.com
 
; <<>> DiG 9.8.3-P1 <<>> @75.75.76.76 google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 8157
;; flags: qr rd ra; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
 
;; Query time: 65 msec
;; SERVER: 75.75.76.76#53(75.75.76.76)
;; WHEN: Tue Mar 26 09:44:09 2013
;; MSG SIZE  rcvd: 12

other than the refused messages while trying via non comcast network, it's working fine for me...
actions · 2013-Mar-26 12:46 pm ·

NetDog
Premium Member
join:2002-03-04
Hollywood, FL

1 recommendation

NetDog to graysonf

Premium Member

2013-Mar-26 1:12 pm

to graysonf
said by graysonf:

DNS servers assigned by DHCP to me are 75.75.75.75 and 75.75.75.76.

However, 75.75.75.76 is not working. Is any one else seeing this?

Can you recheck your DHCP DNS server please? 75.75.75.75 and 75.75.76.76 are the correct DNS servers if you did receive 75.75.75.76 I will need to check the DHCP server.

PM me your cable modem MAC address please; that is if you did get the incorrect address.
actions · 2013-Mar-26 1:12 pm ·

CUBS_FAN
2016 World Series Champs
join:2005-04-28
Chicago, IL

CUBS_FAN to graysonf

Member

2013-Mar-26 3:36 pm

to graysonf
Just choose Google's 8.8.8.8 & 8.8.4.4 or 4.2.2.1 - 4.2.2.6 by GTEI.net and Level3. Personally I'd ping each and see which gives the lowest average ping response.
actions · 2013-Mar-26 3:36 pm ·

NathanO
join:2008-08-21
Seattle, WA

NathanO

Member

2013-Mar-26 3:44 pm

That is generally not advised - using your ISPs DNS servers should give you the best geolocation, and therefore speeds/response times from various CDNs and other services. Comcast is also one of the few that fully support DNSSEC.
actions · 2013-Mar-26 3:44 pm ·

EG
The wings of love
Premium Member
join:2006-11-18
Union, NJ

EG

Premium Member

2013-Mar-26 4:44 pm

FWIW, this appears to be a typo;

75.75.75.76
actions · 2013-Mar-26 4:44 pm ·
EG

EG to CUBS_FAN

Premium Member

2013-Mar-26 4:50 pm

to CUBS_FAN
said by CUBS_FAN:

Personally I'd ping each and see which gives the lowest average ping response.

FWIW, that really doesn't tell the entire story.. Ping can be de-prioritized / rate limited.

Actual resolution time is a better way to gauge DNS prformance.
actions · 2013-Mar-26 4:50 pm ·

NetDog
Premium Member
join:2002-03-04
Hollywood, FL

NetDog to EG

Premium Member

2013-Mar-26 4:56 pm

to EG
said by EG:

FWIW, this appears to be a typo;

75.75.75.76

I agree just wanted to double check where the typo is, you never know
actions · 2013-Mar-26 4:56 pm ·

EG
The wings of love
Premium Member
join:2006-11-18
Union, NJ

1 recommendation

EG

Premium Member

2013-Mar-26 5:48 pm

Understood NetDog See Profile
I was more so replying to the poster.
actions · 2013-Mar-26 5:48 pm ·

NetFixer
From My Cold Dead Hands
Premium Member
join:2004-06-24
The Boro
Netgear CM500
Pace 5268AC
TRENDnet TEW-829DRU
2 edits

NetFixer to graysonf

Premium Member

2013-Mar-26 7:39 pm

to graysonf
I use the Comcast DNS servers both as the default forwarders for my local DNS server, and also directly as secondary, tertiary, etc DNS servers. I have not and do not see any problems with any of the Comcast DNS servers that I use (some manually assigned, and some assigned by DHCP) including the official secondary AnyCast server 75.75.76.76 (I am going to assume that your use of 75.75.75.76 is a typo...if not, then your problem is not with DNS).

FWIW, all of the data displayed below was generated on my Windows server (which is also my local DNS server, and it would be the focal point of any DNS problem seen on my network).

Windows IP Configuration
 
   Host Name . . . . . . . . . . . . : dcs-srv
   Primary Dns Suffix  . . . . . . . : dcs-net
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : Yes
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : dcs-net
                                       dcs-net.net
                                       dyndns-ip.com
 
PPP adapter RAS Server (Dial In) Interface:
 
   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : WAN (PPP/SLIP) Interface
   Physical Address. . . . . . . . . : 00-53-45-00-00-00
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 192.168.9.208
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   Default Gateway . . . . . . . . . :
 
Ethernet adapter Local Area Connection 2:
 
   Connection-specific DNS Suffix  . : dcs-net
   Description . . . . . . . . . . . : Intel 21143-Based PCI Fast Ethernet Adapter (Generic)
   Physical Address. . . . . . . . . : 00-40-F4-2A-31-1E
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   IP Address. . . . . . . . . . . . : 192.168.20.2
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.20.1
   DHCP Server . . . . . . . . . . . : 192.168.20.1
   DNS Servers . . . . . . . . . . . : 192.168.9.2
                                       75.75.75.75
   NetBIOS over Tcpip. . . . . . . . : Disabled
   Lease Obtained. . . . . . . . . . : Tuesday, March 26, 2013 08:26:10
   Lease Expires . . . . . . . . . . : Tuesday, April 02, 2013 08:26:10
 
Ethernet adapter Local Area Connection:
 
   Connection-specific DNS Suffix  . : dcs-net
   Description . . . . . . . . . . . : NETGEAR GA311 Gigabit Adapter
   Physical Address. . . . . . . . . : E0-91-F5-95-BE-AC
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 192.168.9.2
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   IP Address. . . . . . . . . . . . : 2601:5:c80:62:e291:f5ff:fe95:beac
   IP Address. . . . . . . . . . . . : fe80::e291:f5ff:fe95:beac%5
   Default Gateway . . . . . . . . . : fe80::1e7e:e5ff:fe4c:e6ff%5
   DNS Servers . . . . . . . . . . . : 192.168.9.2
                                       75.75.76.76
                                       fec0:0:0:ffff::1%1
                                       fec0:0:0:ffff::2%1
                                       fec0:0:0:ffff::3%1







The results below show that 75.75.76.76 is a bit slower to respond than the other Comcast DNS servers, but it is still reliably responding to queries (the DNS servers with the red lines above and below the IP addresses are servers that did not respond, or responded incorrectly...none of the Comcast servers are in that category):




 Final benchmark results, sorted by nameserver performance:
 (average cached name retrieval speed, fastest to slowest)
 
  192.168.  9.  2 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  + Cached Name   | 0.000 | 0.000 | 0.000 | 0.000 | 100.0 |
  + Uncached Name | 0.023 | 0.072 | 0.237 | 0.065 | 100.0 |
  + DotCom Lookup | 0.020 | 0.027 | 0.057 | 0.008 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
                     dcs-srv.dcs-net
                Local Network Nameserver
 
   68. 87. 68.162 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  - Cached Name   | 0.018 | 0.022 | 0.050 | 0.005 | 100.0 |
  - Uncached Name | 0.021 | 0.064 | 0.230 | 0.055 | 100.0 |
  - DotCom Lookup | 0.019 | 0.028 | 0.051 | 0.008 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
        nrcns.s3woodstock.ga.atlanta.comcast.net
                      Comcast Cable
 
   75. 75. 75. 75 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  + Cached Name   | 0.020 | 0.022 | 0.045 | 0.003 | 100.0 |
  + Uncached Name | 0.023 | 0.067 | 0.244 | 0.061 | 100.0 |
  + DotCom Lookup | 0.021 | 0.028 | 0.056 | 0.009 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
                   cdns01.comcast.net
                      Comcast Cable
 
   68. 87. 72.130 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  - Cached Name   | 0.030 | 0.035 | 0.076 | 0.008 | 100.0 |
  - Uncached Name | 0.033 | 0.081 | 0.273 | 0.063 | 100.0 |
  - DotCom Lookup | 0.032 | 0.042 | 0.084 | 0.013 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
           nrcns.area4.il.chicago.comcast.net
                      Comcast Cable
 
   68. 87. 77.130 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  - Cached Name   | 0.037 | 0.044 | 0.074 | 0.009 | 100.0 |
  - Uncached Name | 0.050 | 0.091 | 0.269 | 0.055 | 100.0 |
  - DotCom Lookup | 0.058 | 0.068 | 0.100 | 0.008 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
        nrcns.westlandrdc.mi.michigan.comcast.net
                      Comcast Cable
 
   68. 87. 74.162 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  - Cached Name   | 0.033 | 0.047 | 0.253 | 0.041 | 100.0 |
  - Uncached Name | 0.039 | 0.091 | 0.282 | 0.062 | 100.0 |
  - DotCom Lookup | 0.063 | 0.072 | 0.088 | 0.007 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
        nrcns.bonitasprngs.fl.naples.comcast.net
                      Comcast Cable
 
   75. 75. 76. 76 |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  + Cached Name   | 0.040 | 0.047 | 0.119 | 0.014 | 100.0 |
  + Uncached Name | 0.048 | 0.093 | 0.245 | 0.052 | 100.0 |
  + DotCom Lookup | 0.078 | 0.087 | 0.095 | 0.005 | 100.0 |
  ---<-------->---+-------+-------+-------+-------+-------+
                   cdns02.comcast.net
                      Comcast Cable
actions · 2013-Mar-26 7:39 pm ·
NetFixer

NetFixer to cp

Premium Member

2013-Mar-26 7:43 pm

to cp
said by cp:

It doesn't appear so.

75.75.75.75 is giving me a connection refused.
75.75.75.76 is timing out...

I'm not on a Comcast network atm...

If you are not on the Comcast network, it is normal for the Comcast DNSSEC servers to not respond to DNS queries. That is by design and is part of Comcast's anti-spoofing protection.
actions · 2013-Mar-26 7:43 pm ·

CUBS_FAN
2016 World Series Champs
join:2005-04-28
Chicago, IL

CUBS_FAN

Member

2013-Mar-27 1:30 pm

said by NetFixer:

said by cp:

It doesn't appear so.

75.75.75.75 is giving me a connection refused.
75.75.75.76 is timing out...

I'm not on a Comcast network atm...

If you are not on the Comcast network, it is normal for the Comcast DNSSEC servers to not respond to DNS queries. That is by design and is part of Comcast's anti-spoofing protection.

Thanks for all the info. I haven't adjusted my DNS servers since the infamous days of Comcast's DNS servers having issues and that time when the someone hacked Comcast with DNS redirects.
actions · 2013-Mar-27 1:30 pm ·
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« Question about speed tier costs • Looking at buying - Speeds drop when I enter my area? »