Internet DRAFT - draft-kawakami-dmm-srv6-gtp6e-reduced
draft-kawakami-dmm-srv6-gtp6e-reduced
dmm Y. Kawakami
Internet-Draft S. Matsushima
Intended status: Informational SoftBank
Expires: 3 September 2024 S. Zadok
Broadcom
D. Yeung
Arrcus, Inc.
D. Voyer
Bell Canada
2 March 2024
SRH Reduction for SRv6 End.M.GTP6.E Behavior
draft-kawakami-dmm-srv6-gtp6e-reduced-01
Abstract
Segment Routing over IPv6 for the Mobile User Plane specifies
interworking between SRv6 networks and GTP-U networks including
required behaviors. This document specifies a new behavior named
End.M.GTP6.E.Red which improves the End.M.GTP6.E behavior more
hardware-friendly by indicating the behavior with one SID.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Distributed Mobility
Management Working Group mailing list (dmm@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/dmm/.
Source for this draft and an issue tracker can be found at
https://github.com/yuyarin/draft-kawakami-dmm-srv6-gtp6e-reduced.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 3 September 2024.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. End.M.GTP6.E.Red Behavior . . . . . . . . . . . . . . . . . . 3
3.1. Control Plane Specification . . . . . . . . . . . . . . . 4
3.1.1. Egress PE . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Ingress PE . . . . . . . . . . . . . . . . . . . . . 5
3.2. Data Plane Specification . . . . . . . . . . . . . . . . 5
3.2.1. Ingress PE . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. Egress PE . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Segment Routing over IPv6 for the Mobile User Plane [RFC9433] defines
interworking between SRv6 [RFC8986] networks and GTP-U [TS.29281]
networks including required behaviors such as End.M.GTP6.E. This
End.M.GTP6.E behavior converts SRv6 packets to GTP-U packets for
downlink(DL) traffic at an egress MUP-PE
[I-D.mhkk-dmm-srv6mup-architecture] when a gNB [TS.23501] is using
IPv6/GTP.
In End.M.GTP6.E behavior, an ingress MUP-PE needs two SIDs in an SRH
with the remote endpoint information (IP address and TEID) in
different places in the SRH and an egress MUP-PE also needs to fetch
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the last SID next to the active SID before outer IPv6 and SRH
decapsulation to restore the IPv6/GTP-U header from those SIDs, in
which current hardware pipelines may be unfamiliar or insufficient to
implement.
This document specifies a new behavior named End.M.GTP6.E.Red which
makes End.M.GTP6.E behavior more hardware-friendly by indicating the
behavior with one SID. This behavior utilizes an Interwork Segment
Discovery (ISD) Route and Type 1 Session Transformed (ST) Route of
MUP SAFI [I-D.mpmz-bess-mup-safi], specified in
[I-D.mhkk-dmm-srv6mup-architecture] to restore the gNB address from
the reduced SRH [RFC8754].
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Terminology
Terminology used in this document is given by [RFC9433] and
[I-D.mhkk-dmm-srv6mup-architecture].
3. End.M.GTP6.E.Red Behavior
End.M.GTP6.E.Red (Endpoint Behavior with encapsulation for IPv6/GTP-U
tunnel with reduced SRH) is used in the interworking scenarios
described in [RFC9433] for the downlink toward the legacy gNB using
IPv6/GTP.
Figure 1 depicts a topology used for the example. This topology is
the same as Figure 4 described in Section 5.3 of [RFC9433] but
terminology is replaced by one used in
[I-D.mhkk-dmm-srv6mup-architecture].
Interwork Segment Direct Segment _______
IP GTP-U SRv6 / \
+--+ +-----+ [N3] +--------+ +--------+ [N6] / \
|UE|------| gNB |------| MUP-PE |--------| MUP-PE |------\ DN /
+--+ +-----+ +--------+ +--------+ \_______/
Egress PE for DL Ingress PE for DL
Figure 1: Example Topology for Interworking
In this topology, we assume the addressing as below:
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* The prefix length of the Interwork Segment, that is, actual RAN IP
Prefix is 'a'.
* The length of the LOC+FUNCT field of the SID for End.M.GTP6.E.Red
behavior on the Egress PE is 'b'.
Figure 2 shows the relationship between RAN IP Prefix, gNB address
and End.M.GTP6.E.Red SID.
0
|
| NLRI in ISD Route 40+b
+----------------------------------------+
| advertised RAN IP Prefix |
+----------------------------------------+
| actual RAN IP Prefix | stuff field |
+--------------------------+-------------+
| a bits | 40-a+b bits |
: : :
: gNB address : : 128
+--------------------------+-------------+-----------------+
| IPv6 address |
+--------------------------+-------------+-----------------+
: /: :
: -------------- : :
: End.M.GTP6.E.Red SID / : :
+-----------------------+----------------+-----------------+
| SRGW-IPv6-LOC-FUNC |Args.Mob.Session| remainder bits |
+-----------------------+----------------+-----------------+
| b bits | 40 bits | 128-40-b bits |
Figure 2: Relationship between RAN IP Prefix and gNB address and SID
In one of deployment scenarios, the length of actual RAN IP Prefixrd
can be 64 bits (a=64) or shorter (a<64) and the length of SRGW-IPv6-
LOC-FUNC can be 48 bits (b=48) in both cases of full SID and uSID.
These are given by the addressing design of the RAN and the SRv6
domain. In this case, the stuff field is 24 bits (or more) and then,
the prefix length of advertised RAN IP Prefix (the NLRI in in the ISD
Route) is 88 bits.
3.1. Control Plane Specification
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3.1.1. Egress PE
If the actual RAN IP Prefix is shorter than b+40 bit-length, then the
Egress PE makes up the missing 40-a+b bits(stuff field) from the gNB
address so that the Egress PE can generate a prefix of b+40 bit
length (advertised RAN IP Prefix).
The Egress PE generates SID prefixes of End.M.GTP6.E.Red behavior
('b' bits of SRGW-IPv6-LOC-FUNC field) for each advertised RAN IP
Prefixes and holds the mapping.
The Egress PE MUST advertise an Interwork Segment Discovery (ISD)
Route [I-D.mhkk-dmm-srv6mup-architecture] which NLRI contains the
advertised RAN IP Prefix with the corresponding SID information.
3.1.2. Ingress PE
The Ingress PE receives a Type 1 Session Transformed (ST) Route
[I-D.mhkk-dmm-srv6mup-architecture] for the UE from the MUP
Controller and an ISD Route for the gNB from the Egress PE. When the
Type 1 ST Route can be resolved with the RAN IP Prefix in the NLRI
field of the ISD Route, the Ingress PE MUST generate a complete SID
value by merging b+40 bit-length SID value stored in the ISD Route
and the last 128-40-b bits of the Endpoint Address (the IPv6 address
of the gNB) then store the complete SID as H.Encaps(.Red) behavior
for the host route of the UE in the FIB.
3.2. Data Plane Specification
3.2.1. Ingress PE
When the Ingress PE receives a packet toward the UE and finds the
corresponding local SID in the FIB, then just perform H.Encaps(.Red)
behavior.
3.2.2. Egress PE
When Egress PE node N receives a packet destined to D, and D is a
local End.M.GTP6.E.Red SID, N does the following:
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S01. Store the IPv6 DA and SA in buffer memory
S02. Pop the IPv6 header and all its extension headers
S03. Push a new IPv6 header with a UDP/GTP-U header
S04. Set the outer IPv6 SA to S
S05. Set the outer IPv6 DA (from buffer memory and mapping)
S06. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields
S07. Set the GTP-U TEID (from buffer memory)
S08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination
Notes:
* The source address S SHOULD be an End.M.GTP6.D SID instantiated at
N or IPv6 address of the UPF.
* The higher b+40 bits IPv6 DA can be restored from the advertised
RAN IP Prefix corresponding to the SID in the mapping, and lower
128-40-b bits can be restored from lower 128-40-b bits of the
End.M.GTP6.E.Red SID (remainder bits field in Figure 2).
* GTP-U TEID is restored from Args.Mob.Session field in the SID as
defined in [RFC9433].
4. Security Considerations
The security considerations for Segment Routing are discussed in
[RFC8402]. More specifically, for SRv6, the security considerations
and the mechanisms for securing an SR domain are discussed in
[RFC8754]. Together, they describe the required security mechanisms
that allow establishment of an SR domain of trust to operate
SRv6-based services for internal traffic while preventing any
external traffic from accessing or exploiting the SRv6-based
services.
The technology described in this document is applied to a mobile
network that is within the SR domain. It's important to note the
resemblance between the SR domain and the 3GPP Packet Core Domain.
This document introduces new SRv6 Endpoint Behaviors. Those
behaviors operate on control plane information, including information
within the received SRH payload on which the behaviors operate.
Altering the behaviors requires that an attacker alter the SR domain
as defined in [RFC8754]. Those behaviors do not need any special
security consideration given that they are deployed within that SR
domain.
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5. IANA Considerations
IANA is requested to allocate, within the "SRv6 Endpoint Behaviors"
[RFC8986] sub-registry belonging to the top-level "Segment Routing
Parameters" registry, the following values:
+=======+=====+===================+===========+
| Value | Hex | Endpoint behavior | Reference |
+=======+=====+===================+===========+
| TBA | TBA | End.M.GTP6.E.Red | This.ID |
+-------+-----+-------------------+-----------+
Table 1: New SRv6 Mobile User-plane
Endpoint Behavior Types
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/rfc/rfc8402>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/rfc/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/rfc/rfc8986>.
[RFC9433] Matsushima, S., Ed., Filsfils, C., Kohno, M., Camarillo,
P., Ed., and D. Voyer, "Segment Routing over IPv6 for the
Mobile User Plane", RFC 9433, DOI 10.17487/RFC9433, July
2023, <https://www.rfc-editor.org/rfc/rfc9433>.
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[TS.29281] 3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", Version 17.4.0, 3GPP
TS 29.281, September 2022,
<http://www.3gpp.org/ftp/Specs/html-info/23501.htm>.
6.2. Informative References
[I-D.mhkk-dmm-srv6mup-architecture]
Matsushima, S., Horiba, K., Khan, A., Kawakami, Y.,
Murakami, T., Patel, K., Kohno, M., Kamata, T., Camarillo,
P., Horn, J., Voyer, D., Zadok, S., Meilik, I., Agrawal,
A., and K. Perumal, "Mobile User Plane Architecture using
Segment Routing for Distributed Mobility Management", Work
in Progress, Internet-Draft, draft-mhkk-dmm-srv6mup-
architecture-06, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-mhkk-dmm-
srv6mup-architecture-06>.
[I-D.mpmz-bess-mup-safi]
Murakami, T., Patel, K., Matsushima, S., Zhang, Z. J.,
Agrawal, S., and D. Voyer, "BGP Extensions for the Mobile
User Plane (MUP) SAFI", Work in Progress, Internet-Draft,
draft-mpmz-bess-mup-safi-03, 5 November 2023,
<https://datatracker.ietf.org/doc/html/draft-mpmz-bess-
mup-safi-03>.
[TS.23501] 3GPP, "System architecture for the 5G System (5GS)",
Version 17.0.0, 3GPP TS 23.501, September 2021,
<http://www.3gpp.org/ftp/Specs/html-info/23501.htm>.
Authors' Addresses
Yuya Kawakami
SoftBank
Email: yuya.kawakami01@g.softbank.co.jp
Satoru Matsushima
SoftBank
Email: satoru.matsushima@g.softbank.co.jp
Shay Zadok
Broadcom
Email: shay.zadok@broadcom.com
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Derek Yeung
Arrcus, Inc.
Email: derek@arrcus.com
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
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