Optimus2357 Premium Member join:2010-11-21 West Warwick, RI |
[DNS] DNS 75.75.75.75Problem: Unable to get online with DNS obtained through DHCP.
Equipment: WNDR3300 (Removed) SB6120 > Direct to Windows 7 laptop
Background: Recently I was helping a friend in Yarmouth MA with some internet issues. After some recent power outages, she was unable to get online. Thinking it was a issue with the router(hard wired to it gave media disco), I bypassed it and went direct, doing a standard power cycle with reboot of-course. I was getting a good IP through DHCP and connection looked good, but I couldn't ping out by domain. I could ping 8.8.8.8 though. After checking I noticed I was getting the DNS 75.75.75.75, but I could not ping it, which I found weird. I didn't really spend too much time isolating the problem, since it was a easy fix; set new router to 8.8.8.8 and 8.8.4.4 and presto, online. I thought Comcast was just having some DNS issues or maybe they were ignoring ICMP, but when I got home (RI, Cox as ISP) I noticed I can now ping 75.75.75.75.
Question: Was there some short term DNS issue in the Yarmouth area? Are those standard DNS for Comcast? My main question is could that be symptomatic of some other problem, perhaps something with the modem? I can't see how, but Im stumped. Any ideas? |
|
NetFixerFrom My Cold Dead Hands Premium Member join:2004-06-24 The Boro Netgear CM500 Pace 5268AC TRENDnet TEW-829DRU
1 edit |
NetFixer
Premium Member
2013-Feb-8 4:00 am
The IP addresses 75.75.75.75 and 75.75.76.76 are the Comcast IPv4 Anycast DNS servers. I see the exact opposite of what you see. If I ping from an AT&T connection, I get no replies as shown below: Pinging 75.75.75.75 (timer gran. 10 ms)...
Ping size: 100 Ping Count: 5
No ping response.
No ping response.
No ping response.
No ping response.
No ping response.
--- 75.75.75.75 ping statistics ---
5 packets transmitted, 0 packets received, 100% packet loss
If I ping from a Comcast connection I get ping replies:
Response from 75.75.75.75 received in 32 milliseconds. TTL = 57
Response from 75.75.75.75 received in 32 milliseconds. TTL = 57
Response from 75.75.75.75 received in 33 milliseconds. TTL = 57
Response from 75.75.75.75 received in 32 milliseconds. TTL = 57
Response from 75.75.75.75 received in 33 milliseconds. TTL = 57
Response from 75.75.75.75 received in 32 milliseconds. TTL = 57
User stopped
Pings sent: 6
Pings received: 6
Pings lost: 0 (0% loss)
Shortest ping time (in milliseconds): 32
Longest ping time (in milliseconds): 33
Average ping time (in milliseconds): 32
I use the Comcast DNS servers in the routers that are connected to Comcast, and also as the default forwarders in my in-house Windows server. I have not seen any Comcast DNS problems in my area at all, but the Anycast system will try to point a user to the nearest "real" Comcast DNS server based on the user's IP address, so it is certainly possible that there were problems in the Yarmouth MA area that would not effect users in other areas. |
|
|
AnonMan
Anon
2013-Feb-8 8:42 am
This has been said multiple times.
Comcast servers wont always return ping results.
For example for me every 1 out of 10 pings gets a reply to that DNS...
Best way to test dns is "nslookup - 75.75.75.75"
It should give you
Server: cdns01.comcast.net Address: 75.75.75.75
At which point you can type a domain and see if it gets results. If not they may have a local issue. That IP can point to a different server based on something as small as the county you are testing from. |
|
Optimus2357 Premium Member join:2010-11-21 West Warwick, RI |
First, thanks for the input. I will have her check, or will check next time I am up that way. I wish I had more time to isolate the issue, but we were in a rush to just get the internet working again. I don't think it was just the servers dropping the ICMP though, since the problem was fixed simply by changing the DNS. Though it could have been a false negative and the problem was elsewhere. Anyone in the Eastern MA area have DNS issues over the last couple days? I know my ISP did in Las Vegas recently and that was caused by a firmware bug in the WNDR3700v1 that basically DoS the DNS servers there. I believe (from what my friend tells me and from the SSID I saw around) Comcast was using Netgear product in the area. Another possibility is something related to IPv6? When working with the router later I noticed my Local area connection would say "No internet access" unless I disabled IPv6 in the IP stack. Likly completely unrelated, but is Comcast set up for IPv6 by default in MA? |
|
Optimus2357 |
to NetFixer
NetFixer, here is ping/trace from home on Cox ISP. Just incase the data is useful to anyone else.
C:\Users\Tim>ping 75.75.75.75
Pinging 75.75.75.75 with 32 bytes of data:
Reply from 75.75.75.75: bytes=32 time=23ms TTL=53
Reply from 75.75.75.75: bytes=32 time=22ms TTL=53
Reply from 75.75.75.75: bytes=32 time=23ms TTL=53
Reply from 75.75.75.75: bytes=32 time=22ms TTL=53
Ping statistics for 75.75.75.75:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 22ms, Maximum = 23ms, Average = 22ms
C:\Users\Tim>tracert 75.75.75.75
Tracing route to cdns01.comcast.net [75.75.75.75]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms 192.168.1.1
2 8 ms 9 ms 11 ms 10.2.120.1
3 9 ms 8 ms 9 ms xxxxxxxxxxxxxxxxxxxx.ri.ri.cox.net [xx.xx.xx.xx]
4 9 ms 13 ms 9 ms ip98-190-33-32.ri.ri.cox.net [98.190.33.32]
5 20 ms 25 ms 48 ms provdsrj01-ae3.0.rd.ri.cox.net [98.190.33.20]
6 14 ms 17 ms 16 ms 68.1.5.161
7 16 ms 15 ms 13 ms te-0-5-0-8-pe02.111eighthave.ny.ibone.comcast.ne
t [173.167.58.101]
8 26 ms 23 ms 25 ms be-16-cr01.newyork.ny.ibone.comcast.net [68.86.8
2.249]
9 16 ms 24 ms 17 ms so-2-1-0-0-ar03.plainfield.nj.panjde.comcast.net
[68.86.91.238]
10 18 ms 19 ms 19 ms xe-6-1-0-0-ar03.ivyland.pa.panjde.comcast.net [6
8.85.63.146]
11 18 ms 18 ms 19 ms so-7-0-0-0-ar04.ivyland.pa.panjde.comcast.net [6
9.139.193.34]
12 26 ms 26 ms 26 ms te-4-1-ur02-d.newcastlerdc.de.panjde.comcast.net
[68.85.158.158]
13 23 ms 31 ms 26 ms cdns01.comcast.net [75.75.75.75]
Trace complete.
|
|
EGThe wings of love Premium Member join:2006-11-18 Union, NJ |
to Optimus2357
FWIW, I have no current problem with CC DNS here in Northern N.J. yet the ping output might make one think so;
Pinging 75.75.75.75 with 32 bytes of data: Reply from 75.75.75.75: bytes=32 time=16ms TTL=57 Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Reply from 75.75.75.75: bytes=32 time=14ms TTL=57 Reply from 75.75.75.75: bytes=32 time=13ms TTL=57 Reply from 75.75.75.75: bytes=32 time=17ms TTL=57 Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Reply from 75.75.75.75: bytes=32 time=19ms TTL=57 Reply from 75.75.75.75: bytes=32 time=11ms TTL=57 Reply from 75.75.75.75: bytes=32 time=14ms TTL=57 Reply from 75.75.75.75: bytes=32 time=16ms TTL=57 Reply from 75.75.75.75: bytes=32 time=19ms TTL=57 Reply from 75.75.75.75: bytes=32 time=16ms TTL=57 Reply from 75.75.75.75: bytes=32 time=14ms TTL=57
Ping statistics for 75.75.75.75: Packets: Sent = 25, Received = 11, Lost = 14 (56% loss), Approximate round trip times in milli-seconds: Minimum = 11ms, Maximum = 19ms, Average = 15ms Control-C ^C
It's ICMP rate limiting / de-prioritization. |
|
pflogBueller? Bueller? MVM join:2001-09-01 El Dorado Hills, CA
1 recommendation |
pflog
MVM
2013-Feb-8 1:40 pm
--- 75.75.75.75 ping statistics ---
8 packets transmitted, 0 packets received, 100.0% packet loss
DNS must be down!!!111 Oh wait... ;) floyd@pflog:~% dig +short A google.com @75.75.75.75
74.125.224.142
74.125.224.135
74.125.224.134
74.125.224.128
74.125.224.131
74.125.224.137
74.125.224.129
74.125.224.133
74.125.224.130
74.125.224.136
74.125.224.132
|
|
graysonf MVM join:1999-07-16 Fort Lauderdale, FL |
to EG
Use TCP pings instead.
C:\tcping -n 15 75.75.75.75 53
Probing 75.75.75.75:53/tcp - Port is open - time=37.329ms Probing 75.75.75.75:53/tcp - Port is open - time=31.564ms Probing 75.75.75.75:53/tcp - Port is open - time=32.282ms Probing 75.75.75.75:53/tcp - Port is open - time=31.473ms Probing 75.75.75.75:53/tcp - Port is open - time=31.542ms Probing 75.75.75.75:53/tcp - Port is open - time=31.381ms Probing 75.75.75.75:53/tcp - Port is open - time=31.530ms Probing 75.75.75.75:53/tcp - Port is open - time=30.522ms Probing 75.75.75.75:53/tcp - Port is open - time=32.468ms Probing 75.75.75.75:53/tcp - Port is open - time=40.081ms Probing 75.75.75.75:53/tcp - Port is open - time=30.714ms Probing 75.75.75.75:53/tcp - Port is open - time=56.208ms Probing 75.75.75.75:53/tcp - Port is open - time=30.913ms Probing 75.75.75.75:53/tcp - Port is open - time=32.016ms Probing 75.75.75.75:53/tcp - Port is open - time=31.956ms
Ping statistics for 75.75.75.75:53 15 probes sent. 15 successful, 0 failed. Approximate trip times in milli-seconds: Minimum = 30.522ms, Maximum = 56.208ms, Average = 34.132ms |
|
EGThe wings of love Premium Member join:2006-11-18 Union, NJ |
EG
Premium Member
2013-Feb-8 5:38 pm
Yes but why reply to me ? Reply to the O.P. as I already know this. |
|
|
jp16 join:2010-05-04 united state |
to Optimus2357
No problems in the Concord MA area. |
|
jlivingood Premium Member join:2007-10-28 Philadelphia, PA |
to Optimus2357
No issues with DNS - the advice of other posters here is correct. Basically ICMP packets have been mean to us so we're not listening to them when we have better things to do. (kidding) The problem was likely something else. |
|