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300 From GSM to LTE-Advanced Pro and 5G

Request message. The message contains the following information elements relevant
to IPv6:

PDN address
PDN Type: IPv4v6
PDN IPv6 Interface ID: 0002:0001:c731:f114
[…]
Container ID: DNS Server IPv6 Address
IPv6: 2a12:577:733:0:10:74:312:312

The IPv6 PDN address is not an IPv6 address but merely the interface identifier the
mobile shall use together with the link local IPv6 prefix in the stateless IPv6 address
auto‐configuration (SLAAC) procedure that will follow. In other words while the net-
work does assign an IPv4 address in the message, it does not assign an IPv6 address or
even an IPv6 prefix yet.
At this point in time the mobile device has an IPv4 address and an interface identifier
that it has to combine with a link local prefix to form an IPv6 link local address from
which it can send an IPv6 Router Solicitation message over the established bearer
(which is also used to transport IPv4 packets). In this example the source IPv6 address
that the mobile device uses is the link local address fe80::2:1:c731:f114 and the destina-
tion address is the link local ‘all routers’ multicast address fe80::2. The network responds
from the link local router multicast address fe80::5 with a Router Advertisement mes-
sage that contains the IPv6 prefix:

Internet Protocol Version 6, Src: fe80::5 (fe80::5), Dst: ff02::1 (ff02::1)
Internet Control Message Protocol v6
Type: Router Advertisement (134)
Code: 0
Checksum: 0x760f [correct]
Cur hop limit: 0
Flags: 0x40
Router lifetime (s): 65535
Reachable time (ms): 0
Retransmission timer (ms): 0
ICMPv6 Option (Prefix information : 2a12:577:9941:f99c::/64)

At this point the mobile device has all information it requires to construct an IPv6
address for itself. To do so it uses the IPv6 prefix it has just received and the interface
identifier received earlier in the Activate Default Bearer message to create the following
IPv6 address:

2a12:577:9941:f99c:0002:0001:c731:f114

3GPP has specified that the mobile can choose any network interface identifier at this
point and can change it for privacy purposes at any time. At this point the mobile has a
global IPv6 address and an IPv6 DNS server address so it is fully configured now to
communicate over IPv6.