Internet DRAFT - draft-dong-spring-sr-4map6-segments
draft-dong-spring-sr-4map6-segments
Network Working Group G. Dong
Internet-Draft C. Xie
Intended status: Standards Track China Telecom
Expires: 17 March 2024 X. Li
CERNET Center/Tsinghua University
S. Peng
Huawei Technologies
14 September 2023
4map6 Segments for IPv4 Service delivery over IPv6-only underlay
networks
draft-dong-spring-sr-4map6-segments-00
Abstract
This document defines two new types of segments for Segment Routing,
i.e., M46S and M46D segments, which are mapping rules based IPv4/IPv6
conversion function running in PE nodes. This segment can be used
for IPv4 service delivery over IPv6-only undelay networks.Both M46S
and M46D are called 4map6 segments. Both M46S and M46D are called
4map6 segments and run in pairs.
Status of This Memo
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This Internet-Draft will expire on 17 March 2024.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Overview of the new SID . . . . . . . . . . . . . . . . . . . 3
3. Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Advertising 4map6 SID . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The document [I-D./draft-ietf-v6ops-framework-md-ipv6only-underlay]
proposes a framework for deploying IPv6-only as the underlay in
multi-domain networks. In this framework, each PE will be identified
by at least one IPv6 mapping prefix, it will also have one or more
associated IPv4 address blocks which are extracted from local IPv4
routing table or address pool. In addition, a specific data
structure called address mapping rule is defined to express the
mapping relationship between IPv4 address blocks and the IPv6 mapping
prefix of the remote PE. With this design, if the mapping rules of
the remote PE are obtained by the ingress PE, the mapping rule will
give the forwarding guidance of IPv4 packet delivery in the IPv6-only
network when the destination address of the IPv4 packet matches its
IPv4 address block, the ingress PE will use the mapping rule to
generate corresponding IPv6 source and destination addresses from its
IPv4 source and destination addresses, and then generate a new IPv6
packet.
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This mapping-based conversion can also work in SRv6 [RFC8986]
networks. SRv6 defines packet processing in IPv6 network as a list
of instructions, which are represented as 128-bit segments, often
called Segment ID (SID). This document defines two new types of
segments for Segment Routing, i.e., M46S and M46D segments, which are
mapping rules based IPv4/IPv6 conversion function running in PE
nodes. In multi-domain IPv6-only networks, the M46S and M46D
segments at the ingress node can convert IPv4 packets into IPv6 ones
by stateless encapsulation or translation, another M46S and M46D
segments at the egress node can restore them to IPv4 packets after
being transmitted in IPv6-only networks.
1.1. Requirements Language
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. Overview of the new SID
SRv6 SID has the same format as a 128-bit IPv6 address, As per
section 3 of [RFC8986], a SID consists of LOC:FUNCT:ARG, where a
locator (LOC) is encoded in the L most significant bits of the SID,
followed by F bits of function (FUNCT) and A bits of arguments (ARG).
+----------+----------------+----------+------------+------------+
| LOC(L bits) | FUNCT(F bits) | ARG(32bits)|
+----------+----------------+----------+------------+------------+
Figure 1: 4map6 SID architecture
The LOC identifies the node which instantiates the SID and will lead
the packets to the node. The FUNCT is an opaque identification of
behavior bound to the SID. ARG field provides additional information
for its processing. As new types of SID, M46S and M46D segments will
follow the format of a general SID. Furthermore, several information
items specific to stateless address mapping and packet conversion are
carried in the relevant fields of the M46S SID and M46D SID, as
below,
• The LOC field is a prefix allocated by operators to identify the
node which instantiates the M46S/M46D SID.
• The FUNCT field identifies the behavior bound to the M46S/M46D SID,
the behavior will be defined in Section 4.
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• The ARG field contains the IPv4 address prefix associated with the
PE node. Since the IPv4 address prefix requires a maximum of 32 bits
of a SID, the value of L+F should be less than or equal to 96.
For the PE node which instantiates M46S/M46D SID, its IPv6 mapping
prefix for IPv4 delivery corresponds to the combination of LOC and
FUNCT fields. Generally, the number of SIDs that can be instantiated
by both M46S SID and M46D SID is equal to the number of associated
IPv4 address blocks.
When an operator instantiates a M46S/M46D SID at an edge node, they
specify a SID value LOC:FUNCT:ARG and the behavior bound to the SID,
An SRv6 endpoint behavior may require additional information for its
processing (e.g. tunnel or translation). This information may be
carried in the control plane, which is out of the scope of this
draft.
3. Behavior
Generally, the M46S/M46D SID nodes run in pairs. For a specific data
flow, one node is ingress PE, denoted by PE1, and the other is egress
PE, denoted by PE2.
All nodes located at the edge of the network need to announce their
M46D SIDs to other nodes. PE2 announces its ability to other nodes
in the format of M46D SID in the SRv6 domain at the control plane.
When PE1 receives the M46D SID announced by PE2, it will bestored in
the local database. This database can store multiple entries, and
each entry includes IPv4 address block, Locator, Function, device
capability and other information corresponding to the SID, The IPv6
mapping prefix, i.e. Locator and Function, represents the egress of
the packet whose destination address is the IPv4 address block.
When PE1 receives an IPv4 packet, it uses the destination IPv4
address block to look for the corresponding IPv4 address block entry
in the local database. If a matching IPv4 address block entry is
found, the corresponding IPv6 mapping prefix will splice the IPv4
destination address to generate a M46D SID, and the 32-bit IPv4
address is placed in the ARG field. Following the general SRv6
procedure, the SID is programmed into SRH.
After that, the IPv4 destination address needs to be spliced with the
corresponding IPv6 mapping prefix, and the M46S SID behavior
identifier is placed in the FUNCT field to generate the M46S SID.
The 32-bit IPv4 source address in the data packet is placed in the
ARG field. Following the general SRv6 procedure, M46S SID is
programmed into SRH.
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The newly generated packet with the SRH is sent into the IPv6-only
network for further delivery. In this case, the source address SA of
the IPv6 packet is the PE1 local address, and the destination address
DA is taken from SRH according to the SRv6 procedure. The process is
shown in the figure below,
+-------------------------------------+
/ \
+----+----+ Multi-domain +----+----+
| PE1 | IPv6-only Network | PE1 |
+----+----+ +----+----+
\ /
+-------------------------------------+
+-----------------------------------+
| IPv6 |
| SA=PE1 |
| DA=PE2 |
+-----------------------------------+
| SRH |
| LOC=PE2 FUNCT=M46D ARG=IPv4 DA |
| LOC=PE1 FUNCT=M46S ARG=IPv4 SA |
+-----------------------------------+
| IPv6 |
+-----------------------------------+
Figure 2: IPv6 packet delivery process carrying M46D and M46S SID
When a new IPv6 packet arrives at PE2, PE2 parses its Locator part.
If it matches the IPv6 mapping prefix instantiated by itself, it
decapsulates the packet according to the instructions in Function,
removes the SRH and IPv6 mapping prefix of the outer layer, and then
forwards it to the next-hop according to the destination IPv4 address
carried in the ARG field.
When a new IPv6 packet arrives at PE2, PE2 resolves the LOC part of
SRH in this packet layer by layer. If it matches the IPv6 mapping
prefix of its own instantiation, it decapsulates the packet according
to the instructions in the FUNCT. Recognition to the FUNCT field
M46S and M46D respectively, to extract the corresponding to the ARG
field source IPv4 address and purpose to carry the IPv4 address
forward IPv4 packet to the next-hop recovery.
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4. Advertising 4map6 SID
In an SRv6 network environment, the M46S/M46D SID needs to be
advertised. The node advertises the M46S/M46D SID,
B:N:FUNCT:ARG,through the control plane together with the SRv6
Endpoint Behavior codepoint identifying the behavior of the SID.
Similar to other types of SIDs, the M46S/M46D SID can be distributed
within and across domains via IGP and BGP or other approaches. The
advertisement method and reachability calculation are specific to the
chosen routing protocol. The distribution of the M46S/M46D Endpoint
Behavior codepoint is left in future documents, e.g. by extending the
SRv6 L3 Service TLV as defined in [RFC9252].
5. IANA Considerations
This document requests IANA to allocate the following codepoints in
"SRv6 Endpoint Behaviors" sub-registry of "Segment Routing
Parameters" top-level registry.
+----------+--------+-----------------------+-----------------+
| Value | Hex | Endpoint behavior | Reference |
|----------|--------|-----------------------|-----------------|
| TBD | | End.M46S | [This.ID] |
+----------+--------+-----------------------+-----------------+
| TBD | | End.M46D | [This.ID] |
+----------+--------+-----------------------+-----------------+
table 1: End.4map6 Endpoint Behavior
6. Security Considerations
There is no additional security risk introduced by this design.
7. References
7.1. 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/info/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/info/rfc8174>.
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[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/info/rfc8402>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
[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/info/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/info/rfc8986>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
7.2. Informative References
[I-D.ietf-v6ops-framework-md-ipv6only-underlay]
Xie, C., Ma, C., Li, X., Mishra, G. S., Boucadair, M., and
T. Graf, "Framework of Multi-domain IPv6-only Underlay
Networks and IPv4-as-a-Service", Work in Progress,
Internet-Draft, draft-ietf-v6ops-framework-md-ipv6only-
underlay-03, 19 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-v6ops-
framework-md-ipv6only-underlay-03>.
Authors' Addresses
Guozhen Dong
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: donggz@chinatelecom.cn
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Chongfeng Xie
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: xiechf@chinatelecom.cn
Xing Li
CERNET Center/Tsinghua University
Shuangqing Road No.30, Haidian District
Beijing
100084
China
Email: xing@cernet.edu.cn
Shuping Peng
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing
100095
China
Email: pengshuping@huawei.com
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