Re: [v6ops] WGLC: draft-ietf-v6ops-unique-ipv6-prefix-per-host-02 - multiple prefixes per device

[Ross Chandler <[e-mail]>]

> On 20 Mar 2017, at 13:01, Alexandre Petrescu <[e-mail]> wrote:
> 
>> "Optionally a single network prefix shorter than the default /64
>> prefix may be assigned to a PDN connection. In this case, the /64
>> default prefix used for IPv6 stateless autoconfiguration will be
>> allocated from this network prefix; the remaining address space from
>> the network prefix can be delegated to the PDN connection using
>> prefix delegation after the default bearer establishment and IPv6
>> prefix allocation via IPv6 stateless address autoconfiguration as
>> defined in clause 5.3.1.2.2.”
>> 
>> “The UE uses DHCPv6 to request additional IPv6 prefixes (i.e.
>> prefixes in addition to the default prefix) from the PDN GW after
>> completing stateless IPv6 address autoconfiguration procedures.”
> 
> This seems to indicate that the PDN GW plays both a role of
> DHCPv6-PD Requesting Router aka DHCPv6 Client (when it gets "assigned" a
> shorter-than-64 prefix) _and_ the role of
> DHCPv6-PD Delegating Router aka DHCPv6 Server (when it delegates
> additional IPv6 prefixes to the UE).
> 
> This is a little bit awkward for setting up routing.
> 
> It would be simpler if the PDN GW were a DHCPv6 Relay.
> 
> Has it been considered to make the PDN GW a DHCPv6 Relay?


In the case of /64 per host, the implementation I’ve seen supplies the prefix needed by SLAAC by having the GW address assignment function generate a DHCPv6 PD request which the GW relays either to an internal DHCPv6 server  or to a central server. That is in a TWAG supplied by one of the draft’s authors. It seems to be done in a way ripe for extension to support UE DHCPv6-PD requests after the initial SLAAC /64 is assigned.

Ross