I've been seeing more and more carriers(and even small ISPs) using asXXXX.net as their domain for rDNS on IP space. What are the pros and cons for doing this versus using your primary business domain name?
Keefe John
I'd say this is mostly for whitelabelling reason rather than a technical one?
Keefe John:
We use just .as domain, like our 29632.as 
Honestly, it looks pretty and you can see the ASN in the traceroute from windows/linux standard traceroute commands.
I don't think it's for white label as most ASN's have a company name in their WHOIS on ARIN/RIPE/ETC.
Short answer: I just like doing it.
Long answer: It allows me to create as many hosts on a segregated domain instead of making my company DNS zone 3000 records long.
And considering browsers use domains to define whether to send cookies or
not along a request, not having access customers on the same domain of your
website is a security benefit.
Rubens
Just been using the .net version of our company domain for router/interface IPs.
Also own the AS<n>.com/net and <ASN>.as though, primarily to not get squatted on.
When you are forced to change your name because of chapter 11, acquisition, rebranding, trademark challenge or a sudden need to distance yourself from previous senior management and their intense hatred of all customers, it's nice not to have to change all your reverse DNS.
Joe