On Jul 4, 2011, at 8:23 PM, John R. Levine wrote: >> Reverse IPv6 caches well. You just can't pre-populate servers with PTR >> records for all 2^64 ptr records in a normal IPv6 subnet. You need to >> use tools that add records for nodes that actually exist. Those tools >> are a decade old now. > > Over in e-mail land, we've been pondering the behavior of spammers, who will likely hop to a different IPv6 address for every spam. If you do rDNS lookups, your cache will fill up with useless entries, maybe PTR, maybe NXDOMAIN, it hardly matters. DNSBLs and DNSWLs, if done the same way as they are in IPv4, have the same problem. These issues are well known in the mail ops community, where it's now the standard advice not to try rDNS lookups on incoming IPv6 mail. Yes, but rDNS PTR lookups always have been pretty much meaningless anyway, and will only get worse in IPv4 due to LSN. Keith _______________________________________________ Ietf mailing list Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf