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Not strictly an ICS issue, but this topic is read by others as well. 


Reverse DNS lookup with IPv4 generally works well, most proper providers at least provide their main name even if the IP is not specially allocated, ie msnbot-157-55-39-2.search.msn.com. 


But IPv6 rDNS is much less useful, mainly because most addresses include 64-bit of effectively random data, which are added to the 64-bits of public address. So my public ranges are 2a00:1940:1:2 and 2a00:1940:2:2, but my remote address is today seen as 2a00:1940:1:2:ed4c:1a97:12fa:c6e7.   I have reverse DNS for my public server addresses like 2a00:1940:2:2::139, but not the random ones. 


Some DNS servers seem able to look-up IPv6 addresses using just the public part of the address, like btcentralplus.com in the UK, but most don't. 


You can find the public name using Whois, but this is not designed for heavy use by a server looking up each new client that connects. 


One solution would seem to be a simple text file with the public names, even just the first 32-bits are enough, 2a00:1940 is Merula my hosting company, 2a02:c7f is BSkyB Broadband,  2a00:1450 is Google, etc.  Has anyone found such a file?


Any other thoughts on reverse DNS for IPv6?




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