[AusNOG] IPv4 - Free /48 from APNIC

Mark Andrews marka at isc.org
Tue Mar 5 14:37:55 EST 2013

In message <CAONJJ+QeTzD4MbcJJh1BgbZTge=A4gJm9hbikVpp5pOwmtBYYA at mail.gmail.com>
, Damian Guppy writes:
> In your example the IPv4 prefix would be 192.168.1 assuming it is a /24
> subnet.
> 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
> --Damian

Below is a real life example of a configured interface.  You will
notice that there are 5 IPv6 addresses configured and one IPv4

There are 2 PA addresses: 2001:470:1f00:820:6233:4bff:fe01:7585 and
2001:470:1f00:820:bc08:aa33:cb4:2af both from the same prefix

There are 2 ULA addresses: fd92:7065:b8e::6233:4bff:fe01:7585 and
fd92:7065:b8e::d40f:effa:ff0a:691f again from the same prefix
fd92:7065:b8e::/64.  The bits 92:7065:b8e were randomly choose by
myself.  The address selection rules are setup such that if this
machine wants to talk to another machine with a address within
fd92:7065:b8e::/48 these addresses will be used otherwise the
2001:470:1f00:820::/64 will be used.  This provides internal
isolation from external renumber events.

There is one link local address fe80::6233:4bff:fe01:7585%en1.
"%en1" maps to a scope id.

The two address with "temporary" are IPv6 privacy addresses.  These
are usually used by clients when they want to talk to a server.
These may or may not have entries in the DNS.  These addresses are
changed periodically.  This machine is always renumbering itself.

The two without "temporary" beside them will normally be used by
services running on the host.  These usually will have entries in
the DNS.

If there was a second provider then there would be another set of

This network is using SLAAC for address assignment hence the autoconf.

% ifconfig en1
	ether 60:33:4b:01:75:85 
	inet6 fe80::6233:4bff:fe01:7585%en1 prefixlen 64 scopeid 0x5 
	inet netmask 0xffffff00 broadcast
	inet6 fd92:7065:b8e::6233:4bff:fe01:7585 prefixlen 64 autoconf 
	inet6 fd92:7065:b8e::d40f:effa:ff0a:691f prefixlen 64 autoconf temporary 
	inet6 2001:470:1f00:820:6233:4bff:fe01:7585 prefixlen 64 autoconf 
	inet6 2001:470:1f00:820:bc08:aa33:cb4:2af prefixlen 64 autoconf temporary 
	media: autoselect
	status: active

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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