Prefix delegation to sub nets

Ole Troan otroan at
Mon Jun 28 10:51:34 CEST 2021

> On 27 Jun 2021, at 23:07, Brian E Carpenter <brian.e.carpenter at> wrote:
> That doesn't work. B needs to get its own /64 prefix(es) from A via DHCPv6-PD ( That's what DHCPv6-PD is for. So A will indeed need to be a DHCPv6 server on its downstream interfaces.

To the extent it matters, it’s not what DHCP PD was designed for.

HNCP does internal prefix assignment in a network. 

Now, if you were to use DHCP PD for this, I would recommend a single PD server in the network (on A).  DHCP PD clients on all internal routers. Either DHCP relays or more simply each internal router PD client configured with the address of the PD server directly. Then an IGP to advertise prefixes. 

The PD clients should request individual /64s for each of their downstream interfaces. 

This scheme does not work great in networks with loops or multiple routers on a link. If using DHCP relays you manually have to make a spanning tree.
And you risk links being assigned multiple prefixes. 

HNCP solves all of this. 


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