[AusNOG] IPv4 - Free /48 from APNIC

Damian Guppy the.damo at gmail.com
Tue Mar 5 14:10:47 EST 2013

In your example the IPv4 prefix would be 192.168.1 assuming it is a /24

In the world of IPv6, just like in IPv4, an address is made up of the
prefix and host parts, so for you example 192.168.1 is the prefix and 1 is
the host, of course IPv6 addresses are Hex and longer, not decimal. In most
setups in IPv6 the host part of the address is determined by the devices
MAC address plus a couple extra bits in the middle, and there are multiple
prefixes assigned by the router/network, as well as a 'local' prefix. In
the end you will often have 3-4 IPv6 addresses per device in this sort of
multi homing setup, all with the same host portion but different prefix
portions. The router can then broadcast if a certain prefix is no longer in
use, or if a new prefix is to be added.

This is just based on my simplistic understanding of it, and its been a
while since ive read up on IPv6 so if im wrong some one feel free to
correct me :P

I do need to do more reading, as I have clients with 5+ sites connected via
MPLS WAN, with 2 of the sites with internet connections from different
providers, and the sites without internet use their wan to route to a site
with internet, and if the site goes down it fails over to the other site
with internet. Not sure how to tackle that in IPv6, NAT on IPv4 meant i
didnt have to think about a lot of this :P


On Tue, Mar 5, 2013 at 10:23 AM, Don Gould <don at bowenvale.co.nz> wrote:

> On 5/03/2013 12:02 p.m., Mark Andrews wrote:
>> The single router solution for IPv6 works today.  You connect to
>> two ISPs.  You send RA's for both prefixes.  If one upstream goes
>> down you deprecate those prefixes.  When the link is restored you
>> stop deprecating those prefixes.  The hosts pick the source address
>> of the active prefix for new outgoing connections.  In terms of
>> availability this is no different than using NAT with IPv4.
> Ok cool.  I'd love to see some scripts for the Mikrotik Router OS showing
> how you set it up to do that.
> I don't understand what impact that has on the devices.
> I don't fully understand this concept of prefixes. where's
> the prefix in that?  192?
> Currently I think in terms of a single address per device.  Are you saying
> all my devices get two addresses and then just use one?
> I don't understand how the devices know which is the least cost route.
>  Alternatively you can have one prefix and establish the VPN link
>> exactly like you did with IPv4 to re-establish connectivity.
>>  Yip, which now requires me to understand how to route v6 over vpn.
> Clearly I need to make a list of all the skills I didn't know I needed just
> to have enough learning to replace my v4 functionality. I wonder what else
> I don't know that I don't know I need to know?
>  The IETF is looking at making the top solution work with multiple
>> routers.  Yes, source + destination based routing is coming to a
>> net near you.
> What?
> D
>> Mark
> --
> Don Gould
> 31 Acheson Ave
> Mairehau
> Christchurch, New Zealand
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