From the perspective of messaging anti-abuse, this can help when that 
department goes to an outside source.  If I see “example.com” and 
“example-hr.com”, is there an easy way today to ensure they’re actually related 
if they’re not registered through the same firm or hosted at the same NS 
systems?  If one can’t definitively determine that, you might decide that they 
are spam/phishing messages, and treat them more harshly when trying to 
determine if they are legit/spam.  For example, I’m pretty sure that 
“google.com” and “google-events.com” aren’t related based on the content of the 
latter’s website, but if I were to receive an email message from 
google-events.com, it might not be as easy to tell.  As for cousin domains, if 
you already know that the malicious domain exists, you can assert a negative 
relationship.  If “example.com” does not know “examp1e.com” exists, there would 
be neither a positive or negative relationship asserted, but the lack of a 
positive (when others are stated positively/negatively), could be used as some 
signal by the evaluator.

--
Alex Brotman
Sr. Engineer, Anti-Abuse & Messaging Policy
Comcast

From: Ben Schwartz <bem...@google.com>
Sent: Tuesday, March 3, 2020 5:38 PM
To: Brotman, Alex <alex_brot...@comcast.com>
Cc: dnsop@ietf.org; Stephen Farrell <stephen.farr...@cs.tcd.ie>
Subject: [EXTERNAL] Re: [DNSOP] RDBD (Related Domains By DNS)

Thanks for the draft.  I haven't been following this, and I found it 
interesting.

I would appreciate more fully worked use cases to explain the motivation.  What 
is the use in correlating different domains?  How would one use this to prevent 
"cousin" attacks?

On Tue, Mar 3, 2020 at 2:12 PM Brotman, Alex 
<alex_brot...@comcast.com<mailto:alex_brot...@comcast.com>> wrote:
Hello,

A while ago, Stephen and I had sent out a few versions of this, and we had some 
discussions and revisions were made.  At the time, discussion waned, however I 
wanted to pick this up again before the onset of IETF107.

https://datatracker.ietf.org/doc/draft-brotman-rdbd/

 I've had some folks contact me privately, and I saw an inquiry on another 
list.  There does seem to be some interest, at least in the anti-abuse and 
research communities, of making this a functional proposition.

To recap, the rough idea is that implementers would be able to positively or 
negatively confirm relationships between domains.  In the world of anti-abuse 
and research, these links are not always obvious.  For example, in a large 
corporation, some teams may go outside acceptable practice and register a 
domain through another provider.  Or it may be that you have international 
branches that operate on a different TLD, but you may not have registered with 
all TLDs.  In the latter case, being able to both positively and negatively 
state a relationship could be useful for anti-spam/phishing.

Any questions or comments would be greatly appreciated.  Thank you.

--
Alex Brotman
Sr. Engineer, Anti-Abuse & Messaging Policy
Comcast

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