Spectrum residential IPv6 rDNS - thank you !

Tue Oct 9 22:42:33 UTC 2018

> On Oct 9, 2018, at 11:37 AM, endre.szabo at nanog-list-kitfvhs.redir.email wrote:
> 
> Hey there,
> 
> On 10/9/18 4:51 PM, Brandon Applegate wrote:
>> Wanted to give a shoutout / thank you to Spectrum for this.  Just noticed today my home PD now has dynamic/synthesized rDNS for IPv6.
> 
> I wonder how they generate these rDNS PTR records? I was always curious, hope someone knows.
> 
> --

I’m guessing synthesized.  There are a couple of dns servers out there that can do this.  An interesting one I just found:

https://all-knowing-dns.zekjur.net

Also my excitement was a bit premature.  It seems that:

1) This is only available from one of the resolvers given out as an IPv6 DNS server (in my region at least) - 2001:1998:f00:1::1  A dig +trace from the internet at large only gets to the NXDOMAIN (which is still much better than a SERVFAIL).

2) Looks like 2001:1998:f00:1::1 is anycasted (as one would expect).  However not all of the instances will consistently return a PTR.

# Simply running dig a handful of times to hit the different anycast boxes…
#
vom at ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
cpe-2607-FCC8-1234-5678-0-0-0-1234.dyn6.twc.com.
vom at ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
cpe-2607-FCC8-1234-5678-0-0-0-1234.dyn6.twc.com.
vom at ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
cpe-2607-FCC8-1234-5678-0-0-0-1234.dyn6.twc.com.
vom at ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
vom at ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
vom at ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
cpe-2607-FCC8-1234-5678-0-0-0-1234.dyn6.twc.com.

I checked 2001:1998:f00:1::1 via whoami.akamai.net and got back a handful of unique IPs.  I’m guessing some inconsistent config or something else has broken on some of the instances...

--
Brandon Applegate - CCIE 10273
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