[plug] IPv6 revisited

Adrian Woodley Adrian at Diskworld.com.au
Wed Jan 15 12:31:32 UTC 2014

G'day Andrew,

The /64 is used to allocate the IP for the end-point of your PPP 
session; ie one IP from this subnet will be used for your router's ppp0 
and another will be used for the BBA/BRAS interface. This is the 
analogous to the dynamic IPv4 address allocated to your router. This IP 
will change every time you reconnect.

The /56 is a static subnet which is permanently allocated to your 
account. You can either allocate the entire /56 to your LAN 
(4,722,366,482,869,645,213,696 IPs!) or break that subnet up into one or 
more /64s (a mere 18,446,744,073,709,551,616 IPs). This is the analogous 
to the private IP space in IPv4 (ie This subnet will 
remain static across reconnections. It is from this range that you 
should allocate IPs to your LAN machines, either via radvd (Neighbour 
Discovery Protocol) or DHCPv6.

I would recommend using a single /64 for your LAN - this leaves you 
options to later on allocate other /64s for networks connected to your 
LAN. For example, I use a second /64 for my laptop, which is routed via 
an IPsec tunnel, giving me IPv6 when I'm away from home. You could even 
do more interesting (paranoid?) things, such as using on /64 for your 
services and another more tightly firewalled /64 for your client machines.



On 13/01/14 16:39, Andrew Cooks wrote:
> Hi Plug
> I recently implemented IPv4 firewalling on our devices at work and
> Phillip Smith's talk on 'husk' for firewalling both IPv4 and IPv6 at
> the LCA Sysadmin miniconf [1] reminded me again that I really need to
> get a proper grip on IPv6.
> So, I followed Adrian Woodley's advice and got an Internode account.
> Internode says I got:
> + A dynamic /64 IPv6 prefix for your PPP session.
> + A static /56 IPv6 prefix for your LAN (if you are using a router
> with Prefix Delegation).
> What's the difference between these two prefixes?
> Adrian's Plug talk on IPv6 could probably answer some of my questions,
> but is still 'private' on youtube.
> Cheers!
> a.
> 1. http://sysadmin.miniconf.org/presentations14.html#PhillipSmith
> _______________________________________________
> PLUG discussion list: plug at plug.org.au
> http://lists.plug.org.au/mailman/listinfo/plug
> Committee e-mail: committee at plug.org.au
> PLUG Membership: http://www.plug.org.au/membership

More information about the plug mailing list