* Owen DeLong
What do you get from SIIT that you don't get from dual stack in a datacenter?
In no particular order: - Single stack is much simpler than dual stack. A single stack to configure, a single ACL to write, a single service address to monitor, staff needs to know only a single protocol, deveopment staff needs only develop and do QA for a single protocol, it's a single topology to document, a single IGP to run and monitor, a single protocol to debug and troubleshoot, one less attack vector for the bad guys, and so on. I have a strong feeling that the reason why dual stack failed so miserably as a transition mechanism was precisely because of the fact that it adds significant complexity and operational overhead, compared to single stack. - IPv4 address conservation. If you're running out of IPv4 addresses, you cannot use dual stack, as dual stack does nothing to reduce your dependency on IPv4 compared to single stack IPv4. With dual stack, you'll be using (at least) one IPv4 address per server, plus a bit of overhead due to the server LAN prefixes needing to be rounded up to the nearest power or two (or higher if you want to accommodate for future growth), plus overhead due to the network infrastructure. With SIIT, on the other hand, you'll be using a single IPv4 address per publicly available service - one /32 out of a pool, with nothing going to waste due to aggregation, network infrastructure, and so on. - Promotes first-class native IPv6 deployment. Not that dual stack isn't native IPv6 too, but I do have the impression that often, IPv6 in a dual stacked environment is a second class citizen. IPv6 might be only partially deployed, not monitored as well as IPv4, or that there are architectural dependencies on IPv4 in the application stack, so that you cannot just shut off IPv4 and expect it to continue to work fine on IPv6 only. With SIIT, you get only a single, first-class, citizen - IPv6. And it'll be the only IPv6 migration/transition/deployment project you'll ever have to do. When the time comes to discontinue support for IPv4, you just remove your IN A records and shut down the SIIT gateway(s), there will be no need to touch the application stack at all. As I said earlier, I will submit an IETF draft about the use case shortly (it seems that the upload page is closed right now, due to the upcoming IETF meeting), and I invite you to participate in the discussion - hopefully, we can work together to address your technical concerns with the solution. I did present the use case at RIPE64, by the way - I hope you will find these links interesting: https://ripe64.ripe.net/archives/video/37 https://ripe64.ripe.net/presentations/67-20120417-RIPE64-The_Case_for_IPv6_O... Best regards, -- Tore Anderson Redpill Linpro AS - http://www.redpill-linpro.com/