Internet DRAFT - draft-du-spring-connection-oriented-srv6
draft-du-spring-connection-oriented-srv6
Network Working Group Z. Du
Internet-Draft P. Liu
Intended status: Standards Track China Mobile
Expires: January 6, 2023 July 5, 2022
Connection-oriented Path in SRv6 Network
draft-du-spring-connection-oriented-srv6-02
Abstract
This document proposes a method to support connection-oriented path
in the SRv6 network. Two related SRv6 Functions need to be supported
on each node along the connection-oriented path.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 6, 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Du & Liu Expires January 6, 2023 [Page 1]
Internet-Draft Connection-oriented Path in SRv6 July 2022
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Data Plane for Connection-oriented Path . . . . . . . . . . . 3
3. Control Plane for Connection-oriented Path . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
SRv6 Network Programming concept is introduced in [RFC8986] and
[I-D.filsfils-spring-srv6-net-pgm-illustration], which enables a data
plane based network programming mechanism that goes beyond mere
packet routing.
According to [RFC8986], an SRv6 SID is defined as the format of
LOC:FUNCT:ARG, where the LOC stands for a locator, the FUNCT stands
for a function, and the ARG is optional and stands for the arguments
of the function. The locator is usually used to route the packet to
the node who generates the SID. The basic functions of SRv6 are End
(related to a node) and End.X (related to a link/adjacency), and many
other functions are also defined, including some VPN related ones and
some binding SIDs. In addition, it is said that even a local VM or
container which can apply any complex processing on the packet can be
defined as a function. The functions may or may not include
arguments.
Based on SRv6, a node in the network can initiate a SID list <SID1,
SID2, SID3> for a flow, so that a packet of the flow would be routed
to the first node where the function1 related to SID1 would be
implemented, then be routed to the second node where function2
related to SID2 would be implemented, and trigger similar operations
according to SID3.
In fact, both MPLS and SRv6 are some kind of languages that support
network programming. By using a label to represent a VPN instance,
MPLS provides a good support to the VPN services in the network.
SRv6 now shows a more powerful capability in network programming.
Du & Liu Expires January 6, 2023 [Page 2]
Internet-Draft Connection-oriented Path in SRv6 July 2022
Perhaps in future, a lot of new network characteristics would be
developed based on SRv6; meanwhile, some old network characteristics
may also be realized by using SRv6 in order to integrate network
protocols, and simplify the network. This document gives an example
of the later.
Traditional MPLS transport is not source routing based, but is label
switching based. In MPLS networks, we can establish a label
switching path for a specific flow. It looks like a connection-
oriented path. If using the current SRv6 mechanism, we need to
initiate a SID list <SID1, SID2, SID3, ...> that includes every node
along the path, which is inconvenience. This document proposes a new
SRv6 mechanism to support the connection-oriented path by defining
two new functions on the node.
The motivation to support the connection-oriented path in SRv6 is
that sometimes a strict hop-by-hop TE path is needed in the network,
such as a DetNet path defined in RFC 8655 [RFC8655]. In one
realization of DetNet, each node along the path need allocate
specific resources to the critical traffic, and a fixed path must be
used. In future, the network may evolve to a pure SRv6 network
without MPLS. In this situation, SRv6 should support some old
network characteristics, such as the connection-oriented
characteristic mentioned in this document.
2. Data Plane for Connection-oriented Path
Data plane for a connection-oriented path in SRv6 is easy to design.
We just need to define a new End.XCopd function, which is similar to
END.X (binding to a cross-connected adjacency in Layer-3), but
includes a label argument. The function needs to be supported on
each node along the path, and it is used to support the connection-
oriented path on the data plane.
When receiving a packet with an End.XCopd SID S as the Destination
Address (DA), the node will match the SID in "My SID Table" to ensure
that S is generated by itself, and also check whether the label is
valid. If all checks are ok, the node should be able to obtain the
outgoing SID S2 in the "My SID Table". The node should replace the
DA with the outgoing SID S2, and forward the packet to the layer-3
adjacency bound to the SID S.
The penultimate node along the path will find that the connection-
oriented path is about to terminate, so that it will do normal End.X
operations, i.e., decrement SL, update the IPv6 DA with SRH[SL], and
forward the packet to the layer-3 adjacency bound to the SID.
Du & Liu Expires January 6, 2023 [Page 3]
Internet-Draft Connection-oriented Path in SRv6 July 2022
_______ _______ _______ _______ _______
| Node1 |----| Node2 |----| Node3 |----| Node4 |----| Node5 |
------- ------- ------- ------- -------
Node1: <A1::, A2::End.XCopd:ARG2>
Node2: <A1::, A3::End.XCopd:ARG3>
Node3: <A1::, A4::End.XCopd:ARG4>
Node4: <A1::, A5::End.DT4>
Figure 1: <SA, DA> changes along the Connection-oriented Path
on the data plane
Figure 1 shows an example of label switching in SRv6. It is assumed
that each NodeX has a locator as AX. Node 1 generates a packet to
Node 5 with an SRH header: <A1::End.XCopd:ARG1, A5::End.DT4> and an
<SA, DA> pair: <A1::, A1::End.XCopd:ARG1>. And it is assumed that
A1::End.XCopd:ARG1 can match a "switching table" entry: incoming SID
A1::End.XCopd:ARG1, outgoing SID A2::End.XCopd:ARG2, and an interface
binding to this End.XCopd:ARG1 function. Hence, after the process of
"label switching", the Node 1 sends out a packet with an SRH header:
<A1::End.XCopd:ARG1, A5::End.DT4> and an <SA, DA> pair: <A1::,
A2::End.XCopd:ARG2>.
We assume that the Node 2 has a switching table entry: incoming SID
A2::End.XCopd:ARG2, outgoing SID A3::End.XCopd:ARG3, and an interface
binding to that End.XCopd:ARG2 function, so that the packet will be
sent to Node 3, and then Node 4.
We also assume that the Node 4 has a switching table entry: incoming
SID A4::End.XCopd:ARG4, outgoing SID A5::End.XCopd:0003, and an
interface binding to that End.XCopd function. When the label "0003"
appears, it means the node is the penultimate node. The Node 4 will
do normal End.X operations, and sends out a packet without an SRH
header, but with an <SA, DA> pair: <A1::, A5::End.DT4>.
The switching table should be established in advance on each node
along the path, and it demonstrates the mapping relationship of the
incoming SID and the outgoing SID. In the first hop of the path, it
also demonstrates the mapping relationship of the first SID and the
connection-oriented path. The way by which the label switching table
is established on each node is described in the following section.
3. Control Plane for Connection-oriented Path
A PCE-based/controller-based method can surely configure each node
along the path with a proper label switching table. However, this
document also provides another optional mechanism for the distributed
control plane. In fact, this method looks like what the RSVP-TE does
Du & Liu Expires January 6, 2023 [Page 4]
Internet-Draft Connection-oriented Path in SRv6 July 2022
in the MPLS network defined in RFC 3209 [RFC3209]. In other words,
we can simulate some basic functions of RSVP-TE by using SRv6 network
programming.
We need to define a new End.Copc function, which is used to establish
and maintain the connection-oriented path in the SRv6 network. The
function needs to be supported on each node along the path.
The End.Copc function also includes a label argument. Some of the
label space should be reserved. In this document, we suppose that
the label "0000" stands for the path establishment procedure. If a
node receives a packet with an End.Copc function as the DA with a
label value "0000", the node will trigger the path establishment
procedure just as what the PATH message does in RSVP-TE. If a node
receives a packet with an End.Copc function as the DA with a normal
label value, the node will use the downstream label to establish a
label switching table entry just as what the RESV message does in
RSVP-TE.
However, in this way, the Head-End needs to notify each node along
the path by some means, and we do not have a notification mechanism
between different nodes in the data-plane network programming now.
This document suggests to enable a simple notification method for the
data-plane network programming if the information is not that
complicated. For example, we can send a "ping" message with a
specific TLV containing the necessary information. The advantage is
easy to inter operate.
_______ _______ _______ _______ _______
| Node1 |----| Node2 |----| Node3 |----| Node4 |----| Node5 |
------- ------- ------- ------- -------
Node1: <A1::, A2::End.Copc:0000> --->>
Node2: <A1::, A3::End.Copc:0000> --->>
Node3: <A1::, A4::End.Copc:0000> --->>
Node4: --->> <A1::, A5::Copc:0000>
Node5: <<--- <A1::, A4::Copc:0003>
Node4: <<--- <A1::, A3::End.Copc:0117>
Node3: <<--- <A1::, A2::End.Copc:0445>
Node2: <A1::, A1::End.Copc:0998> <<---
Figure 2: <SA, DA> changes along the Connection-oriented Path
on the control plane
Figure 2 shows an example of label switching path establishment in
SRv6. Node 1 generates a "ping" packet with an <SA, DA> pair: <A1::,
A1::End.Copc:0000>. A new TLV defined for "ping" would include each
End.Copc functions along the path, and the TLV is supposed to be in
Du & Liu Expires January 6, 2023 [Page 5]
Internet-Draft Connection-oriented Path in SRv6 July 2022
the payload of the "ping" message. And it is assumed that
A1::End.Copc:0000 can match the "My SID Table", and the DA is
replaced by A2::End.Copc:0000 after the Node 1 has read the specific
TLV in the payload. Then, Node 1 sends the packet to the Node2
according to the new DA. Similar operation takes place in Node2-4.
Node 5 will find it is the last SID after reading the specific TLV in
the payload. It generates a label "0003", and sends back the packet,
as a response packet. In this time, the "ping" packet has an <SA,
DA> pair: <A1::, A4::Copc:0003>. Based on the information in the
response packet, Node 4 can generate a label "0117", and establish a
swapping table entry: incoming SID A4::End.XCopd:0117, outgoing SID
A5::End.XCopd:0003, and an interface binding to the A4's End.XCopd
function.
Similarly, the Node 3 can generate a label "0445", and establish a
swapping table entry: incoming SID A3::End.XCopd:0445, outgoing SID
A4::End.XCopd:0117, and an interface binding to the A3's End.XCopd
function.
The Node 1 will find it is the first SID after reading the specific
TLV in the payload of the "ping" message, and optionally, it can also
generate a label "1111", and establish a swapping table entry:
incoming SID A1::End.XCopd:1111, outgoing SID A2::End.XCopd:0998, and
an interface binding to the A1's End.XCopd function.
The swapping table is used in this document for the convenience of
description. In fact, it should be several entries in the "My SID
Table". We can also define some label for the procedure of releasing
the path in future version of the draft.
4. IANA Considerations
TBD.
5. Security Considerations
TBD.
6. Acknowledgements
TBD.
7. References
Du & Liu Expires January 6, 2023 [Page 6]
Internet-Draft Connection-oriented Path in SRv6 July 2022
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>.
[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>.
7.2. Informative References
[I-D.filsfils-spring-srv6-net-pgm-illustration]
Filsfils, C., Garvia, P. C., Li, Z., Matsushima, S.,
Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R., and
J. Leddy, "Illustrations for SRv6 Network Programming",
draft-filsfils-spring-srv6-net-pgm-illustration-04 (work
in progress), March 2021.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
Authors' Addresses
Zongpeng Du
China Mobile
No.32 XuanWuMen West Street
Beijing 100053
China
Email: duzongpeng@foxmail.com
Du & Liu Expires January 6, 2023 [Page 7]
Internet-Draft Connection-oriented Path in SRv6 July 2022
Peng Liu
China Mobile
No.32 XuanWuMen West Street
Beijing 100053
China
Email: liupengyjy@chinamobile.com
Du & Liu Expires January 6, 2023 [Page 8]
