Page 316 - From GMS to LTE

302 From GSM to LTE-Advanced Pro and 5G

IPv6 tethering, it (and not the cellular network) returns a Router Advertisement message
to the link local address of the device containing the following information, as shown in
Figure 4.30:
IPv6 Prefix;
●
MTU size (maximum packet size);
●
Link layer address of the router;
●
DNS server information.
●
Sending the DNS server IPv6 address as part of the Router Advertisement is not
supported by all devices. Devices that do not implement this set the ‘other’ flag in the
message to advise the device to query for the DNS server’s IPv6 address with a separate
message.
With the IPv6 prefix contained in the Router Advertisement message the device then
proceeds and assembles its own IPv6 address, typically by concatenating the prefix and
its MAC address as its interface identifier. As for the link local address, the device then
sends a Neighbor Solicitation message over the network to see if another device already
uses this IPv6 address.
For privacy reasons IPv6‐capable devices usually do not use an IPv6 address with
their MAC address as the interface identifier but generate a second IPv6 address with a
random interface identifier. Again, a Neighbor Solicitation message is sent to make sure
it is unique. If no answer is received the process is complete and the device is ready to
communicate over the Internet using IPv6.

Figure 4.30 An IPv6 Router Advertisement sent during tethering. Source: Gerald Combs / Wireshark.