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jlivingood
Premium,VIP
join:2007-10-28
Philadelphia, PA
kudos:2
reply to NetFixer

Re: [DNS] Comcast DNS connectivity issues

I wonder if it was really DNS...

From NANOG:


Re: Bell Canada outage?
From: Darius Jahandarie
Date: Wed, 8 Aug 2012 14:35:41 -0400
On Wed, Aug 8, 2012 at 2:31 PM, Zachary McGibbon
wrote:
Anyone at Bell Canada / Sympatico can tell us what's going on? Our routing table is going nuts with Bell advertising a lot of routes they shouldn't be

Bell leaked a full table. To add to the fun, it seems that TATA took the full table and releaked it.

--
JL
Comcast


NetFixer
Snarl For The Camera Please
Premium
join:2004-06-24
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Reviews:
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1 edit

said by jlivingood:

I wonder if it was really DNS... ;-)

From NANOG:


Re: Bell Canada outage?
From: Darius Jahandarie
Date: Wed, 8 Aug 2012 14:35:41 -0400
On Wed, Aug 8, 2012 at 2:31 PM, Zachary McGibbon
wrote:
Anyone at Bell Canada / Sympatico can tell us what's going on? Our routing table is going nuts with Bell advertising a lot of routes they shouldn't be

Bell leaked a full table. To add to the fun, it seems that TATA took the full table and releaked it.

If it wasn't it a Comcast DNS problem ir was doing a really good job of imitating a Comcast DNS problem since both AT&T and Level3 DNS worked.

Here is a repost of the DNS query results from my previous post:

C:\>nslookup test-ipv6.com 4.2.2.1
Server:  a.resolvers.level3.net
Address:  4.2.2.1
 
Non-authoritative answer:
Name:    test-ipv6.com
Address:  216.218.228.114
 
C:\>nslookup test-ipv6.com 68.94.156.1
Server:  dnsr1.sbcglobal.net
Address:  68.94.156.1
 
Non-authoritative answer:
Name:    test-ipv6.com
Address:  216.218.228.114
 
C:\>nslookup test-ipv6.com 75.75.75.75
Server:  cdns01.comcast.net
Address:  75.75.75.75
 
DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
*** Request to cdns01.comcast.net timed-out
 
C:\>nslookup test-ipv6.com 68.87.68.162
Server:  nrcns.s3woodstock.ga.atlanta.comcast.net
Address:  68.87.68.162
 
DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
*** Request to nrcns.s3woodstock.ga.atlanta.comcast.net timed-out
 
 


I also had access to http://test-ipv6.com when using their DNS servers (as was also shown in my previous post), and I had no problems doing a ping or traceroute to 216.218.228.114 which doesn't even use DNS (perhaps I should have saved and posted those results as well); all of which indicated to me that the routing to the site from my Comcast connection was fine.

I will concede that it is certainly possible that something external to Comcast's DNS servers might have been responsible. However, the end result for someone using Comcast DNS servers was still a Comcast DNS problem (which did not effect AT&T or Level3 DNSSEC servers). Whatever the low level cause, it was fortunately quickly resolved and I reverted to using Comcast DNS servers for my external DNS query forwarding shortly after it started working again.

FWIW, the reason for my previous post was just for the sake of accuracy because I had earlier posted in this thread that I had never had a problem with the Comcast DNSSEC servers. I have certainly also seen similar brief site specific problems using DNS servers from AT&T, Level3, et al in the past (and if they had also been unable to resolve test-ipv6.com I would have not bothered to make my previous post).

--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.