Re: [v6ops] DHCPv6-PD presence on OSs, and GTP question (was: 464xlat case study (was reclassify 464XLAT as standard instead of info))

[Alexandre Petrescu <[e-mail]>]

Mikael,

I would like to reply, and also ask a few GTP questions publicly.

Le 28/09/2017 à 10:53, Mikael Abrahamsson a écrit :
> On Thu, 28 Sep 2017, Erik Kline wrote:
> 
>> I can just feel all the "android and dhcpv6" screeds being written 
>> right now...
> 
> Do any other mobile operating systems do DHCPv6 on the GTP tunnel?

I have seen DHCPv6-PD Solicits on Android and on Sierra Legato OS.

> It's been too many years since I last looked at GTP packet traces to 
> remember if this was done or not.

Having loooked at GTP packet traces, I suppose one looked at 3GPP specs
as well.

I would like to ask whether by 3GPP specs the GTP packets can optionally
be transported in IPv6 messages?

3GPP spec "GTP" Rel 15 of September 2017 says this:
> UDP/IP is the only path protocol defined to transfer GTP messages in
>  the version 1 of GTP. A User Datagram Protocol (UDP) compliant with
>  IETF RFC 768 [13] shall be used.

In practice, a packet capture on PGW shows an IPv6 DHCPv6-PD Solicit
message, preceded by a GTP-U Header, which is itself preceded by a "GTPU
Rx PDU" which is an IPv4 UDP packet.

The UDPv4 port number that transports GTP packets is 2152, reserved at
IANA and at that 3GPP spec.

This is the example packet capture I am talking about:

Friday August 11 2017
INBOUND>>>>>  15:45:22:470 Eventid:142004(3)
GTPU Rx PDU, from [IPv4-address]:2152 to [IPv4-address2]:2152 (129)
TEID: 0x80072183, Message type: GTP_TPDU_MSG (0xFF)
Sequence Number:: NA
GTP HEADER FOLLOWS:
              Version number: 1
               Protocol type: 1 (GTP C/U)
[snip]
GTP HEADER ENDS.
            Payload protocol: IPv6
PROTOCOL PAYLOAD FOLLOWS:
fe80::b9d9:c10a:2c2d:3c3b.546 > ff02::2.546:  [udp sum ok]
IPv6 Header Follows:
[snip]
IA_PD Option Follows:
                 Option Type: 0x0019 (OPTION_IA_PD)
                Option Length: 0x0029
                        IA ID: 0x00000000 (0)
                           T1: 0x00000e10 (3600)
                           T2: 0x00001518 (5400)
IA_PD Prefix Option Follows:
                  Option Type: 0x001a (OPTION_IA_PD_PREFIX)
                Option Length: 0x0019 (25)
               IA Prefix Addr: ::/56
                      PL Time: 0x00000e10 (3600)
                      VL Time: 0x00001518 (5400)
[hlim 1] (len 81)
PROTOCOL PAYLOAD ENDS.