Re: Spectrum residential IPv6 rDNS - thank you !

[Brandon Applegate <brandon () burn net>]

> On Oct 9, 2018, at 11:37 AM, endre.szabo@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@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@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@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@ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
vom@ice:~$ dig +short @2001:1998:f00:1::1 -x 2607:fcc8:1234:5678::1234
vom@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...



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Brandon Applegate - CCIE 10273
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