DNSBLs and IPv6
From time to time I see people arguing that the wide deployment of IPv6 will force DNSBLs to significantly change their operations and semantics. Usually they have little or no actual experience with IPv6 and the main argument used to justify this view appears to be more or less "OMG so many bits!1!!!".
I have no reason to believe that this will really happen. People are already sending mail over IPv6 and I expect that the same reputation mechanisms used for IPv4 will be deployed as soon as they will be needed, with small policy changes to cope with the fact that end users typically get a whole network instead of a single IP address.
So I expect that DNSBLs will continue to operate as usual like they currently do for IPv4 addresses, optionally by promoting "single IP" listings to "whole /64" listings when appropriate.
Let's briefly categorize the common types of DNSBL listings:
- spam sources or spam support (e.g. SBL): a human investigator decides that a specific server or network needs to be listed. Nothing will change.
- dynamic or dynamic-like (residential) networks (e.g. PBL): a human investigator decides that a specific network needs to be listed, or the ISP itself provides their relevant ranges. Nothing will change, except that dynamically-assigned networks will be much less common.
- fully automatic behaviour-driven listings (e.g. CBL): the IP addresses of spam sources are automatically listed as soon as they are detected. Are adjustments needed for this case? The only issue I can think about are the randomly-generated "privacy extensions" addresses used by some clients, but since they can be automatically detected the BL operator may also choose to just list the corresponding /64 from start.
If anything, with IPv6 much less guessing is needed to know how large each customer assignment is, so some things will actually be easier for operators.
(I have been using IPv6 for at least ten years and I have received email over IPv6 networks for at least five.)