[ipv6hackers] Question on DHCPv6 address assignment

Tore Anderson tore at fud.no
Sat Feb 1 11:44:53 CET 2014

* Fernando Gont

> 1) What's the pattern with which addresses are generated/assigned? Are
> they sequential (fc00::1, fc00::2, etc.)?  Random? Something else?

The DHCPv6 server in an Cisco EPC3928 (but probably also EPC3925) will
by default hand out EUI-64 based host identifiers. So it probably looks
at the MAC address of the incoming requests, runs the EUI-64 algorithm
on it, and presents that back in the IA_NA offer. To thoroughly confuse
the hosts it also advertises the prefix in RA with the A bit set.

I suggested to my ISP that they ask Cisco to change this behaviour,
whether or not they did I don't know.

> 2) What about their stability? Is there any intent/mechanism for them to
> be as "stable" as possible? Or is it usual for hosts to get a new
> address for each lease?

It'll remain stable for as long as the client's MAC address remains stable.


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