Paulie, a frustrated enterprise IPv6 early adopter summarized his pains in a comment to my “Small-site multihoming in IPv6: mission impossible?” post saying “[IPv6/IPv6 support] is a mess and depressing” and asked “Is it too late to go to CLNS?”
Quite a few old-timers (I’m definitely one of them) lament the glory days of VMS, DECnet Phase V and CLNP, but while CLNP was a viable alternative for the next-generation IP in 1993, it would fare worse than IPv6 today.
The reason is very simple: IPv4 has evolved significantly in the last 15 years. It got all the nifty features that supposedly made IPv6 a better protocol (IPsec, QoS, autoconfiguration). There are also several decades of operational experience and gradual improvements that allowed us to build large-scale reasonably-manageable somewhat-secure networks.
IPv6 was definitely a better protocol than IPv4 in 1995, but then it got shelved for 15 years and while everyone was improving IPv4, nobody ported those improvements to IPv6 ... until we woke up, realized we had only a year or two left until IPocalypse and started dusting the by-now arcane protocol that barely anyone touched for more than a decade.
In the meantime, we also forgot what it means to be multiprotocol. The networking old-timers still have a vague remembrance of times when routers forwarded more than just IP packets, but the application programmers never had to think in multiprotocol terms. Have you ever seen an application that was able to run across IP and DECnet or across IPX and IP ... concurrently? The too-low-level socket API and lack of session layer don’t help promote the multiprotocol deployment either.
The imminent (this time unavoidable) IPv4 address shortage has finally forced practically-minded and operations-focused people to start addressing IPv6 shortcomings and although the solutions are late, they are appearing. For example, DNS configuration is now standardized as part of IPv6 autoconfiguration mechanism. It’s true that it took more than a decade till everyone agreed configuring host parameters might also include configuring the DNS server address, but at least we’re making progress.
I doubt anyone touched CLNP recently (at least I haven’t seen many features appearing in Cisco IOS) and while it was a stable protocol 15 years ago (and still is), it lacks more features than IPv6 does. CLNP host implementations are also rare; IPv6 is ubiquitous in modern operating systems (apparently including iOS). Going back to CLNP is thus no longer an option.