simple DHCPv6 config with /56-Prefix

[Simon]

Adam Nielsen <a.nielsen at shikadi.net> wrote:

> Note that if you put all your DHCP clients in one /64 and your servers
> in another /64, all traffic between the two subnets will transit via
> your router.  Assuming all machines are connected to the same switch
> this is quite inefficient, as all network traffic will be pushed
> through a single host (your router) even when the machines could
> have communicated with each other directly via the switch.

This is not true in the IPv6 world. All it needs is for a router to advertise that both prefixes are on-link and the hosts can communicate directly. This is one area where IPv6 is fundamentally different (better) than IPv4.
For completeness, a router can advertise that a prefix is not on-link - meaning that communications between hosts in the same prefix must communicate via the gateway. This can be the case in some non-broadcast networks, or networks where device-device direct communications is blocked (e.g. for privacy/security in public WiFi).

However ...
While you can use any prefix length you like, in practice there are many things that won’t work properly in anything but a /64. If using DHCP* then you possibly aren’t using SLAAC*, so this is somewhat more fluid, but I would work on the assumption that sooner or later you’ll come across something that assumes prefixes are never anything but /64 and breaks if even anything else.

* This will prevent Android devices using the network as Google (for idealogical reasons) refuses to support DHCP, and not only doesn’t provide a client, but actively blocks others from providing one.

Simon