Re: [v6ops] GTP questions

[Ca By <[e-mail]>]

On Sun, Nov 12, 2017 at 4:11 AM Alexandre Petrescu <
[e-mail]> wrote:

> Hi Mikael,
>
> Sorry for late reply.
>
> Le 29/09/2017 à 10:44, Mikael Abrahamsson a écrit :
> > On Fri, 29 Sep 2017, Alexandre Petrescu wrote:
> >
> >> 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.
> >
> > It's an implementation detail whether this is carried over IPv4 or
> > IPv6. UDP can be carried by both. If you read 29.060 it talks about
> > GTP over both IPv4 and IPv6:
> >
> > "If an IPv4/IPv6 capable SGSN received IPv4 GGSN addresses from the
> > old SGSN, it shall include IPv4 addresses in the fields SGSN Address
> > for Control Plane and SGSN Address for User Traffic and IPv6
> > addresses in the fields Alternative SGSN Address for Control Plane
> > and Alternative SGSN Address for User Traffic. Otherwise, an
> > IPv4/IPv6 capable SGSN shall use only SGSN IPv6 addresses if it has
> > GGSN IPv6 addresses available. If the GGSN supports IPv6 below GTP,
> > it shall store and use the IPv6 SGSN addresses for communication
> > with the SGSN and ignore the IPv4 SGSN addresses. If the GGSN
> > supports only IPv4 below GTP, it shall store and use the IPv4  SGSN
> > addresses for communication with the  SGSN and ignore the IPv6 SGSN
> > addresses. When active contexts are being redistributed due to load
> > sharing, G-PDUs that are in transit across the Gn-interface are in
> > an undetermined state and may be lost."
> >
> > "below GTP" seems to indicate what protocol GTP is run over.
>
> YEs, I can agree to read it that way, but it can be a little bit of a
> stretch.  GTP Rel15 Sept. 2017 clearly says only RFC768.  If it wanted
> to mean GTP/UDP/IPv6 it could have cited e.g. RFC6936.  Hence the doubt.
>
> But yes, I agree with you that in largest part UDP works over IPv6 as
> over IPv4.
>
> > There is a lot more text in TS 29.060 regarding this, but interested
> > parties can read it and form their own opinion.
>
> I agree.
>
> > To me it's clear that 3GPP has done the work to try to achieve so you
> > can standards-based build a network with no IPv4 addresses used for
> > infrastructure. If this works in real life in shipping products,
> > that's a whole other question.
>
> I agree that real life in shipping products is a whole other question.
>
> I had some discussion with some people, and here are some of my
> deductions.  If I am wrong, I carry the responsibility.
>
> Operator1 in hexagon country: the IPv6 is carried in GTP/UDP/IPv4
> Operator2 in country voted out of EU: the IPv6 is carred in GTP/UDP/IPv4.
>
> Among other cellular operators that offer IPv6 to smartphones, I wonder
> about the following:
>
> Is T-Mobile USA carrying the smartphone's IPv6 inside GTP/UDP/IPv4?  Or
> inside GTP/UDP/IPv6?
>
> Is Reliance JIO in India carrying the smartphone's IPv6 inside
> GTP/UDP/IPv4?  Or inside GTP/UDP/IPv6?
>
> My gut feeling is that all do GTP/UDP/IPv4.
>

Your gut is correct, i do not know of any carrier using GTP with ipv6
transport.

That said, i believe the GTP transport network operations is orthogonal to
the network that the UE / customer traffic experiences.



> My intention with this discussion is twofold: find an operator that does
> GTP/UDP/IPv6 and second to deduce something for the IPv6-only
> terminology draft.
>
> Alex
>
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