Tag Archives: IPv6 Prefix

2001:db8::/32 in the Wild

If you have ever read some docs or RFCs about IPv6 you should be quite familiar with the 2001:db8::/32 “IPv6 Address Prefix Reserved for Documentation”, RFC 3849. This RFC clearly states how you should handle addresses within this range: “This assignment implies that IPv6 network operators should add this address prefix to the list of non-routeable IPv6 address space, and if packet filters are deployed, then this address prefix should be added to packet filters.”

I was interested whether those addresses are actually used in the Internet. For this purpose I analyzed my firewall logs for 6 months to get an idea. Though it was not that much, I actually got a couple of connections inbound and outbound (!) sourced or destined to those reserved IPv6 addresses.

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IPv6 Interface ID Structure

While there are many approaches on how to structure your IPv6 prefix into /64 subnets (blogposts, books, talks) there are only a few hints what you can do with the other 64 bits of the addresses, namely the IPv6 interface identifier or IID. To my mind you can put some (but not too much) logic into those IIDs to a) have some structure for your addresses that b) helps you identifying those addresses when seeing them in logs or anywhere else. Hence it is easier for you to remember the IPv6 address behind a name (forward DNS) as well as the host when seeing the address (reverse DNS).

This post just shows the approach I am using in my lab. You might find it useful or you might disagree completely. Anyhow, feel free to comment your experiences or solutions for that. :D I am wondering why there isn’t much discussion about these IIDs at all. Maybe for some good reasons I am not seeing yet?

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