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

[Ross Chandler <[e-mail]>]

> On 21 Mar 2017, at 09:52, Alexandre Petrescu <[e-mail]> wrote:

>> 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.
> 
> Sounds promising.
> 
> We wrote a python DHCPv6 client called "PD tester" that issues DHCPv6 PD
> requests to cellular networks.  We tested it on a one cellular network
> and no answer until now.
> 
> We would like to test it on other cellular networks.
> 
> Is the TWAG applied in some cellular network?

There’s no cellular access but it is very similar. All the clients are using their WiFi interfaces, their access is tunnelled to the GW where each client gets its own unique /64 by SLAAC.
If the gateway and UE could do DHCPv6-PD over both WiFi & 3GPP interfaces as described in TS.23401 then shorter than /64 prefixes could be assigned in a common manner.

Here is a further quote from TS.23401 clause 5.3.1.2.6 on how the DHCPv6 should operate 

"The total IPv6 address space available for the PDN connection (UE default bearer prefix and UE PDN connection IPv6 address space pool) shall be possible to aggregate into one IPv6 prefix that will represent all IPv6 addresses that the UE may use. If the UE had indicated that it supports prefix exclusion and the prefix to be delegated to the UE includes the /64 prefix that was allocated to the PDN Connection, the PDN GW shall utilise the prefix exclusion feature as specified for DHCPv6 Prefix Delegation in IETF RFC 6603 [70].

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. The UE acts as a "Requesting Router" as described in RFC 3633 [21] and inserts one or more IA_PD option(s) into a DHCPv6 Solicit message sent from the UE to the PDN GW. The PDN GW acts as the DHCP server and fulfils the role of a "Delegating Router" according to RFC 3633 [21]. The UE optionally includes the RAPID_COMMIT option in the DHCPv6 Solicit message to trigger two-message DHCPv6 procedure instead of the four-message DHCPv6 procedure. The UE shall include OPTION_PD_EXCLUDE option code in an OPTION_ORO option to indicate support for prefix exclusion. In response to the DHCPv6 Solicit message, the UE receives a DHCPv6 Reply message with one or more IA_PD prefix(es) for every IA_PD option that it sent in the DHCPv6 Solicit message. The PDN GW delegates a prefix excluding the default prefix with help of OPTION_PD_EXCLUDE. Prefix exclusion procedures shall follow IETF RFC 6603 [70].”



Ross