Ivan Pepelnjak over at Cisco IOS Hint and Tricks (an absolute must-read site) has a nice post about the use of IPv4 addresses as the router ID in OSPFv3. I touched on this in this Question of the Day.
This part of the post made me laugh out loud:
One of the obscure facts of IPv6 OSPF (OSPFv3) is that it uses a 32-bit router ID like OSPFv2. It’s a reasonable choice, I haven’t seen an OSPF network with more than a billion routers yet.
I love the “yet” qualifier. :-)