SPRING Working Group Z. Li
Internet-Draft C. Li
Intended status: Standards Track Huawei Technologies
Expires: October 22, 2021 April 20, 2021
SRv6 End.M behavior for traversing MPLS Networks
draft-li-spring-srv6-end-mpls-00
Abstract
As the development of cloud computing, increasing services have been
migrated from enterprise sites to clouds, so the connection between
sites and clouds are critical for enterprises.
SRv6 provides a sourcing routing mechanism to connect the enterprise
sites and clouds by programming the end-to-end path at the ingress
node. In this scenario, the SRv6 packets may traverse multiple
network domains and some of them may not be SRv6-capable.
In order to support SRv6 end-to-end path programming, this document
defines the mechanism of SRv6 traversing MPLS networks, which
supports encoding MPLS tunnel information in the SRH.
Status of This Memo
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This Internet-Draft will expire on October 22, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. MPLS Path Programming in SRv6 . . . . . . . . . . . . . . . . 3
3.1. END.M . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. MPLS Tunnel Information in SRH TLV . . . . . . . . . . . 6
4. Illustration . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
When Segment routing (SR) [RFC8402] is deployed on the IPv6 data
plane, it is called SRv6 [RFC8754]. For support of SRv6, a new
routing header called Segment Routing Header (SRH), which contains a
list of SIDs and other information, has been defined in [RFC8754].
When deploying SRv6, the SRv6 network may need to interwork with
exiting networks, such as MPLS netwoks and IPv4 networks.
With the development of cloud computing, increasing services have
been migrated from enterprises to cloud data centers. Compared with
interconnections between branches and headquarters, new connections
between enterprise sites to cloud data centers and inter-cloud are
added, which bring new requirements and challenges for existing
networks. [I-D.li-rtgwg-ipv6-based-con] describes the requirements
and candidate technologies in IPv6-based Cloud-oriented Networking
(CON). In IPv6-based CON, SRv6 can be used to connect enterprise
sites and clouds. In this scenario, an SRv6 packet may be forwarded
traversing MPLS domains or IPv4 domains.
In order to specify the MPLS tunnel, End.BM [RFC8986] has been
defined for binding an SR-MPLS policy to an SRv6 SID currently. The
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MPLS tunnel information is maintained at the ingress node of the MPLS
tunnel, which will introduce states to the node, and it also require
extra configuration at the node allocating End.BM SIDs.
This document defines a new mechanism to carry MPLS tunnel
information in the SRv6 packet, so that no configuration of SR-MPLS
policy is required at the intermediate node, and end-to-end path
programming traversing MPLS domains can be supported.
2. Terminology
This document makes use of the terms defined in [RFC8986], and the
reader is assumed to be familiar with that terminology.
2.1. 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.
3. MPLS Path Programming in SRv6
This document defines the following mechanisms for SRv6 traversing
MPLS networks.
3.1. END.M
In order to indicate the start of SR-MPLS tunnel information, a new
SRv6 behavior End.M (End with SR-MPLS path instantiation) is defined.
An End.M SID MUST be encoded preceding the MPLS tunnel information,
therefore it can not be the last SID in the SID list.
The path of traversing SR-MPLS domain is called SR-MPLS sub-path. An
SR-MPLS sub-path can be encoded by an End.M and the following MPLS
label stack as shown in the following figure.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ... |
| MPLS Tunnel Information |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End.M SRv6 SID |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. SR-MPLS Sub-path Encoding in G-SRH
The MPLS tunnel information include multiple MPLS labels, and they
are aligned with 128 bits. Therefore padding is needed if there are
less than 4 MPLS labels in a 128-bit space.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 0 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 1 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 2 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 3 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 0 | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 1 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(b)
Figure 2. MPLS tunnel information Encoding
The S-bit of the last MPLS label in the SID list MUST be set
indicating the end of the MPLS label stack.
When a node processes an End.M SID, it copies the following MPLS
label stack of SR-MPLS sub-path to the MPLS header, and set the IPv6
DA as the SRv6 SID after the MPLS label stack, and then forward the
packet according to the active MPLS label.
When node N receives a packet whose IPv6 DA is S and S is a local
End.B4 SID, the line S13-S16 from the End processing [RFC8986] is
replaced by the following:
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S13. Set SL pointing to the next SID after MPLS label stack.
S14. Update IPv6 DA with Segment List[Segments Left]
S15. Push a MPLS label stack before the IPv6 header
by using the MPLS label stack.
S16. Lookup the active MPLS label and forward the packet
S17. }
3.2. MPLS Tunnel Information in SRH TLV
Using SRH TLV is another option of carrying MPLS tunnel information.
In order to retrive the MPLS tunnel information from SRH TLV, a new
behavior End.MT (End with SR-MPLS path instantiation by using SRH
TLV) should be defined, and this will be described in the future.
A mechanism of specifying which SRH TLV to be processed by which SID
in the SID list is defined in
[I-D.li-spring-srh-tlv-processing-programming], and it can be used
for indicating the node to process MPLS tunnel information in SRH
TLV.
[Editor's note] Also, there may be some other solutions to indicate
and carry MPLS tunnel information in the SRv6 packet, for example
using the argument of a SID to indicate the MPLS label stack or
number of MPLS labels.
More details will be described in the future.
4. Illustration
For easy understanding, this section illustrates how to use End.M SID
to specify the MPLS tunnel.
Assuming that
o A::1:100 is the End.M SID allocated by the ingress node of an SR-
MPLS domain.
o 1001, 1002, 1003, and 1004 are the labels for an SR-MPLS sub-path.
Therefore, the programmed SRv6 path for traversing SR-MPLS/MPLS
domain is shown in Figure 2.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1004 | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1003 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1002 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1001 | TC |0| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A::1:100 (End.M) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. Carrying MPLS tunnel information in SID list
5. IANA Considerations
TBD
6. Security Considerations
TBD
7. Acknowledgements
8. References
8.1. 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>.
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[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>.
[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>.
[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>.
[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>.
8.2. Informative References
[I-D.li-spring-srh-tlv-processing-programming]
Li, C., Xia, Y., Dhody, D., and Z. Li, "SRH TLV Processing
Programming", draft-li-spring-srh-tlv-processing-
programming-00 (work in progress), December 2020.
[I-D.li-rtgwg-ipv6-based-con]
(editor), C. L., Li, Z., and H. Yang, "IPv6-based Cloud-
Oriented Networking (CON)", draft-li-rtgwg-ipv6-based-
con-01 (work in progress), March 2021.
Authors' Addresses
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
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Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: c.l@huawei.com
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