Re: SLAAC, Static & DHCPv6 day 1 interoperability issue

[Philip Homburg <[e-mail]>]

>    The operational issue with
>    SLAAC not supporting any prefix length in PIO and requirement
>    for the 64 bit boundary is that in a deployment scenario where
>    you would like to deploy longer prefix length subnets with a
>    mix of server hosts with static address and mix of client hosts
>    with managed address M=1 that get their 128 bit address from
>    the DHCPv6 server pool, the fear has always been that if a device
>    came up on the subnet that only supports SLAAC it would not work
>    due to the SLAAC A flag set and 64 bit IID requirement.  In that
>    case the SLAAC host would not be able to communicate with any
>    of the devices with a longer prefix including the router.  

In this scenario, the SLAAC host would not get a global address, but would
still have a link local address. Communication with routers happens
using link local addresses, so I don't see how that could be an issue.

If the host wants to send a packet to a global address and the host only has
a link local address, then host generates a packet with a link local address
as source address. If the destination global address is onlink, then the
host can directly use ND to find the L2 address of the target.

If the destination is not onlink, then the destination could still be on
the same subnet, so the host would send the packet to the default router.
The default router would then forward the packet to the destination on the
same link. Obviously, this last part is rarely used, so it would not 
surprise me if there are bugs.