Hi,
During the last DMM meeting there was discussion about using DHCPv6 to
request addresses, and to qualify these addresses ('sustained',
'nomadic', etc.)
There was comment that it may not be good to use DHCPv6 to request
addresses, but rather use SLAAC for that, or use DHCPv6-PD to request
prefixes, not addresses. This is RECOMMENDED in RFC 7934 section 8:
Due to the drawbacks imposed by requiring explicit requests for
address space (see Section 4), it is RECOMMENDED that the network
give the host the ability to use new addresses without requiring
explicit requests. This can be achieved either by allowing the host
to form new addresses autonomously (e.g., via SLAAC) or by providing
the host with a dedicated /64 prefix. The prefix MAY be provided
using DHCPv6 PD, SLAAC with per-device VLANs, or any other means.
There is however a use-case I am concerned with which needs DHCPv6 for
addresses. The use case involves a M2M Router connecting to 4G and
giving access with USBnet to other routers and hosts in its moving network.
The M2M Router hears a /64 prefix from the operator, forms multiple /80
prefixes for its 'inner' routers and hosts, a DHCPv6 Server, and listens
to DHCPv6 requests for addresses from these 'inner' routers and hosts.
In this case, SLAAC does not work for these inner hosts, because the
prefix length is /80.
This is why DHCPv6 for addresses is needed in this use-case.
The operator does not implement DHCPv6 Prefix Delegation, and I think
there is no 4G operator at this time that implements it. I have some
ongoing discussions with an incumbent operator about DHCPv6-PD on
Ericsson base stations (not to name them), but I think nobody else is
doing it at this time.
_If_ a cellular operator implements DHCPv6-PD, and _if_ it delivers
plens shorter than /64 to cellular UEs, then the need for
DHCPv6-for-addresses may disappear. My gut feeling at this time is that
we are way way far from such a time.
Alex
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