Data held by ISPs

Ian Batten igb at
Sun Dec 28 16:28:07 GMT 2014

> When IPv.6 really gets going I suspect that most IPs will be fixed.

It depends on what you mean by "most".  Most fixed line (DSL, Cable, etc) will be fixed, because
ISPs will probably get one or more /40 and therefore will obtain addresses in blocks of 2^24.  Very
few ISPs have more than 16 million fix-line customers, and the few that do will have either multiple
/40s or something larger.

However, the mobile operators will probably use SLAC or DHCPv6 to allocate addresses within a single /64
per [some network organisational block], and most mobile devices use RFC 4941 privacy extensions
(and sometimes can't turn them off: I get really annoyed that all the iDevices at home get fresh
IPv6 addresses every hour).  Given |mobile devices|>|fixed lines|, most IPs will in fact be dynamic.


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