Just stumbled upon this article http://www.networkworld.com/news/tech/2007/090507-tech-uodate.html
Suggested here is that Dual Stack is more attractive than tunneling. Is the advise here based on real life experience or is it a matter of what is good for the goose may not be good for the gander?
The article is written for enterprise network administrators, not for ISPs. If you are an ISP, the two main options are to dual-stack or to use MPLS with 6PE. Even if your network does not have an MPLS core today, you should still consider whether it makes sense to use MPLS with 6PE as your migration path to IPv6. Every network is different so there is really no panacea here. As for tunnels, I expect that everybody uses them somewhere in the network. There are lots of different kinds of tunnels, more than mentioned in the article. For ISP purposes, you could build an IPv6 overlay network instead of either dual-stacking or MPLS with 6PE. For small to midsize ISPs this may make a lot of sense. For larger ISPs, they will likely do some of this to accommodate their 2nd and 3rd tier PoP locations. The important thing about tunnels is to make sure that they are well-designed and well-maintained. The most important aspect of maintaining a tunnel, is making sure that you get rid of it when it is no longer the best solution. MPLS is based on tunneling. Lots of broadband access is based on tunnels. Pseudo-Wire Emulation is based on tunnels. --Michael Dillon