IP/Network

IPv6 - LTE

Getting into LTE. You would know that Network allocate a UE IP in the PDN address IE of Activate Default EPS Bearer Request. Then the question would be "how do I specify IPv6 or IPv4v6 in this information element". Do I have to put in the whole 128 bits ? or only part of 128 bits ? If I am supposed to put in only parts of the address, whichpart do I have to specify ?

The answer is "specify Interface Identifier" in PDN information element. (Refer to 3GPP 24.301 section 9.9.4.9 PDN address)

For example, if the interface indentifier that you want to allocate the UE is 0000:0000:0102:0002, the PDN value would be as follows.

  +-PDN address ::= LV

  | +-Octet1 ::= DIVISION

  | | +-Length of PDN address contents ::= LEN (0..255) [9]

  | +-Octet2 ::= DIVISION

  | | +-spare ::= FIX [0]

  | | +-PDN type value ::= CHOICE [IPv6]

  | +-Octet3-14 ::= DIVISION

  |   +-PDN address information ::= OCTETARRAY SIZE(0..12) [0000000001010002]

What if the IP type is IPv4v6 dual stack ? The answer is "you have to concatenate IPv6 and IPv4 in such a manner that IPv6 comes first and IPv4 comes after". If the interface identifier of UE is 0000:0000:0102:0002 and IPv4 address is 10.10.10.10, the address you have to specify in PDN is as follows.

  +-PDN address ::= LV

  | +-Octet1 ::= DIVISION

  | | +-Length of PDN address contents ::= LEN (0..255) [13]

  | +-Octet2 ::= DIVISION

  | | +-spare ::= FIX [0]

  | | +-PDN type value ::= CHOICE [IPv4v6]

  | +-Octet3-14 ::= DIVISION

  |   +-PDN address information ::= OCTETARRAY SIZE(0..12) [00000000010100020A0A0A0A]

Regardless of whether it is IPv6 or IPv4v6, once UE received Activate Default/Dedicated Bearer Request and respond it with Activate Default/Dedicated Bearer Accept message, UE initiate the IPv6 auto configuration process which is known as Router Discovery or Network Discovery process ("Router Solicitation"/"Router Advertisement"). UE send "Router Solicitation" to the router and router should reply with "Router Advertisement". One example process that I captured using Wireshark is as follows.

Now the question is "What would happen if UE failed to get the reply (Router Advertisement) from the router ?".  To be honest, I haven't confirmed on this behavior from any specification, but as far as I experienced with sever devices that I have tried,  UE retries two or three times and send "EMM Detach Request" if it still fail to get Router Advertisement.