I’m perpetually behind reading some big mailinglists, so today, a month after the fact, I discovered this message about deploying IPv6 on the North American Network Operators Group list.

In the message, Kevin Day writes about his experiences deploying IPv6 in what seems to be an enterprise network. Some things work well, others are simply different from IPv4, but some things don’t work very well. I haven’t seen the reachability issues to the degree he experienced, except that IPv6 is indeed sometimes slower than IPv4 for file transfers and I disagree with him about the routing/addressing issues. However, there is one important issue that I think needs to be addressed:

“Once we got everything on the network and server side ready for and usable on IPv6 we discovered that a lot of our client’s applications just had no idea what to do with IPv6 connections. Many PHP applications broke because they expected $_SERVER[’REMOTE_ADDR’] to fit within 15 characters at most. Databases had to have their columns widened (if they were storing the address as text), or functionality had to be rewritten if they were storing IPs as 32 bit integers. Web server log analyzers claimed that the log was “corrupted” if it had an IPv6 address in it. Lots and lots of application logic just wasn’t IPv6 aware at all, and either had serious cosmetic problems with displaying IPv6 addresses, or simply didn’t work when an IPv6 address was encountered.”

IP addresses show up in many places, and in almost all cases, the handling of these addresses must be tweaked to work with IPv6. It would be good if software makers started making the necessary changes sooner rather than late With nearly 1.5 billion IPv4 addresses still available and 165 million being used up in 2005 it seems we have a lot of time, but (if nothing changes) we’re out of IPv4 addresses in 8 years, which means that people will start moving to IPv6 en masse in 5 years. The software you write today probably won’t be used anymore in 5 years, but the software you write two or three years from now very likely will.

(If anyone has any questions about any of the other issues that come up in the message, leave a comment or email me.)