Network Working Group X. Geng
Internet-Draft Z. Li
Intended status: Informational M. Chen
Expires: January 14, 2021 Huawei
July 13, 2020
SRv6 for Deterministic Networking (DetNet)
draft-geng-spring-srv6-for-detnet-01
Abstract
Deterministic Networking provides service with low jitter, bounded
latency and low loss rate, using technologies of explicit route,
resource reservation and service protection.This document specifies
how to implement Deterministic Networking (DetNet) in a SRv6 Network.
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.
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Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on January 14, 2021.
Copyright Notice
Copyright (c) 2020 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SRv6 for DetNet Overview . . . . . . . . . . . . . . . . . . 4
4. Service Protection . . . . . . . . . . . . . . . . . . . . . 5
4.1. Service Protection Scenarios . . . . . . . . . . . . . . 5
4.2. Data Plane Considerations . . . . . . . . . . . . . . . . 7
4.3. Control Plane Considerations . . . . . . . . . . . . . . 7
5. Resource Reservation . . . . . . . . . . . . . . . . . . . . 8
5.1. Resource Reservation Scenarios . . . . . . . . . . . . . 8
5.2. Data Plane Considerations . . . . . . . . . . . . . . . . 10
5.3. Control Plane Considerations . . . . . . . . . . . . . . 10
6. Explicit Route . . . . . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
10. Normative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
With more and more applications running in the Internet, quality of
the service gains more and more attention, especially for some new
applications, for example Cloud VR, Cloud Game, HDV (high-definition
video) and so on, SLA (Service Level Agreement), including jitter,
delay and loss rate, influences the users' experience significantly.
So SLA guarantee is an important issue which requires new
technologies and solutions for the network.
Deterministic Networking (DetNet defined in [RFC8655]) provides a
capability to carry specified data flows for real-time applications
with extremely low data loss rates, low jitter and bounded latency
within a network domain. Techniques used include: 1) providing
explicit paths for DetNet flows that satisfies the SLA requirement
from user and do not immediately change with the network topology; 2)
reserving data plane resources for DetNet flows along the allocated
path of the flow; 3) replicates DetNet flows into two or more copies
and transport different copies through different path in parallel,
called service protection.
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Segment Routing(SR) leverages the source routing paradigm. An
ingress node steers a packet through an ordered list of instructions,
called "segments". SR can be applied over IPv6 data plane using
Routing Extension Header(SRH, [RFC8754]). A segment in Segment
Routing is not limited to a routing/forwarding function. An SRv6
Segment can indicate functions that are executed locally in the node
where they are defined.
[I-D.filsfils-spring-srv6-network-programming] describes some well-
known functions and segments associated to them. SRH TLVs([RFC8754])
also provides meta-data for segment processing. All these features
make SRv6 suitable to carry DetNet flows, by defining new segments
associated with DetNet functions and meta data for DetNet.
This document describes the concepts needed by implementing DetNet in
an SRv6-based domain and provides considerations for any
corresponding implementation.
Editor's note: DetNet is limited in a controlled network domain, and
it is not the only method to provide SLA guarantee. But it is a good
start to discuss how to use SRv6 to have a SLA-guaranteed network
service.
2. Terminology
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 [RFC2119].
Terminologies for DetNet go along with the definition in [RFC8655]
and [RFC8754]:
DetNet domain
The portion of a network that is DetNet aware. It includes end
systems and DetNet nodes
DetNet edge node
An instance of a DetNet relay node that acts as a source and/ or
destination at the DetNet service sub-layer. For example, it can
include a DetNet service sub-layer proxy function for DetNet
service protection (e.g., the addition or removal of packet
sequencing information) for one or more end systems, or starts or
terminates resource allocation at the DetNet forwarding sub-layer,
or aggregates DetNet services into new DetNet flows. It is
analogous to a Label Edge Router (LER) or a Provider Edge (PE)
router.
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DetNet relay node
A DetNet node including a service sub-layer function that
interconnects different DetNet forwarding sub-layer paths to
provide service protection. A DetNet relay node participates in
the DetNet service sub-layer. It typically incorporates DetNet
forwarding sub-layer functions as well, in which case it is
collocated with a transit node.
DetNet transit node
A DetNet node operating at the DetNet forwarding sub-layer, that
utilizes link layer and/or network layer switching across multiple
links and/or sub-networks to provide paths for DetNet service sub-
layer functions. Typically provides resource allocation over
those paths. An MPLS LSR is an example of a DetNet transit node.
End system
End systems of interest to this document are either sources or
destinations of DetNet flows. And end system may or may not be
DetNet forwarding sub-layer aware or DetNet service sub-layer
aware.
DetNet service sub-layer
DetNet functionality is divided into two sub-layers. One of them
is the DetNet service sub-layer, at which a DetNet service, e.g.,
service protection is provided.
DetNet forwarding sub-layer
DetNet functionality is divided into two sub-layers. One of them
is the DetNet forwarding sub-layer, which optionally provides
resource allocation for DetNet flows over paths provided by the
underlying network.
3. SRv6 for DetNet Overview
As mentioned above, there are mainly three technologies/functions
defined in DetNet: Explicit Route, Resource Reservation and Service
Protection. Explicit Route is the basic of the other two
technologies, and guarantees the path satisfies the SLA requirement
from application. Resource Reservation protects DetNet flows from
network congestion, which could reduce the end-to-end latency and
congestion loss; Service Protection prevents DetNet flow from random
media errors and equipment failures, which makes the loss rate
extremely low.
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In [RFC8655], DetNet functionality is implemented in two sub-layers
in the protocol stack: the DetNet service sub-layer and the DetNet
forwarding sub-layer. The DetNet service sub-layer provides DetNet
service, e.g., service protection. The DetNet forwarding sub-layer
supports DetNet service in the underlying network, by providing
explicit routes and resource allocation to DetNet flows. There is no
obvious protocol stack as MPLS, in SRv6 both service sub-layer and
forwarding sub-layer are implemented through SRH.
The following picture shows that a general DetNet enabled network
defined in [RFC8655] :
TSN Edge Transit Relay DetNet
End System Node Node Node End System
+----------+ +.........+ +----------+
| Appl. |<--:Svc Proxy:-- End to End Service -------->| Appl. |
+----------+ +---------+ +---------+ +----------+
| TSN | |TSN| |Svc|<- DetNet flow --: Service :-->| Service |
+----------+ +---+ +---+ +--------+ +---------+ +----------+
|Forwarding| |Fwd| |Fwd| | Fwd | |Fwd| |Fwd| |Forwarding|
+-------.--+ +-.-+ +-.-+ +--.----.+ +-.-+ +-.-+ +---.------+
: Link : / ,-----. \ : Link : / ,-----. \
+........+ +-[ Sub ]-+ +.......+ +-[ Sub ]-+
[Network] [Network]
`-----' `-----'
In SRv6 for DetNet, the outer IPv6 Header with the SRH is used for
carrying DetNet flows. Explicit path is instantiated in the segment
list of SRH, and other functions/arguments for service protection
(packet replication, elimination and ordering, PREOF) and resource
reservation (packet queuing and scheduling) are also defined in the
specified SID. Meta data for DetNet could be instantiated in the
Optional TLVs.
4. Service Protection
4.1. Service Protection Scenarios
The figure below shows that an IPv6 flow is sent out from the end
station E1. The packet of the flow is encapsulated in an outer
IPv6+SRH header as a DetNet SRv6 packet in the Ingress(In) and
transported through an SRv6 DetNet domain. In the Egress(Eg), the
outer IPv6 header+SRH of the packet is popped, and the packet is sent
to the destination E2.
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| |
----IPv6--->|<---------------SRv6 DetNet------------->|<----IPv6---
| |
| +------+T2+----+ |
+---+ +---+ +-+-+ +-+-+ +---+ +---+
| E1+----| In|--+T1+--+R1 | |R2 |--+T4+--| Eg+----+ E2|
+---+ +---+ +-+-+ +-+-+ +---+ +---+
+-----+T3+-----+
The DetNet packet processing is as follows:
Ingress:
Inserts the SRv6 Policy that will steer the packet from Ingress to
the destination
The methods and mechanisms used for defining, instantiating and
applying the policy are outside of this document. An example of
policies are described in [I-D.ietf-spring-segment-routing-policy]
Flow Identification and Sequence Number are carried in the SRH.
Relay Node 1(Replication Node):
Replicates the payload and IPv6 Header with the SRH. This is a
new function in the context of SRv6 Network Programming which will
associate a given SID to a replication instruction in the node
originating and advertising the SID. The replication instruction
includes:
* The removal of the existing IPv6+SRH header
* The encapsulation into a new outer IPv6+SRH header. Each
packet (the original and the duplicated) are encapsulated into
respectively new outer IPv6+SRH headers.
Binding two different SRv6 Policies respectively to the original
packet and the replicated packet, which can steer the packets from
Relay Node 1 to Relay Node 2 through two tunnels.
Relay Node 2(Elimination Node):
Eliminates the redundant packets.
Binds a new SRv6 Policy to the survival packet, which steers the
packet from Relay Node 2 to Egress.
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Egress:
Decapsulates the outer Ipv6 header.
Sends the inter packet to the End Station 2.
The DetNet packet encapsulation is illustrated here below. It has to
be noted that, in the example below, the R2 address is a SRH SID
associated to a TBD function related to the packet replication the
node R1 has to perform. The same (or reverse) apply to node R2 which
is in charge of the discard of the duplicated packet. Here also a
new function will have a new SID allocated to it and representing the
delete of the duplication in R2.
End Station1 output packet: (E1,E2)
Ingress output packet: (In, T1)(R1,T1, SL=2)(E1,E2)
Transit Node1 output packet: (In, R1)(R1,T1,SL=1)(E1,E2)
Relay Node1 output packets : (R1,T2)(R2,T2,SL=2)(E1,E2),
(R1,T3)(R2,T3,SL=2)(E1,E2)
Transit Node2 output packet: (R1, R2)(R2,T2,SL=1)(E1,E2)
Transit Node3 output packet: (R1, R2)(R2,T3,SL=1)(E1,E2)
Relay Node2 output packet: (R2, T4)(Eg,T4,SL=2)(E1,E2)
Transit Node4 output packet: (R2, Eg)(Eg,T4,SL=1)(E1,E2)
Egress out : (E1,E2)
4.2. Data Plane Considerations
Flow Identification and sequence number are necessary in the
encapsulation of SRv6 for DetNet in order to support service
protection. Replication nodes decide which DetNet flows are supposed
to be replicated by identifying the flow with the flow
identification. Elimination nodes decide whether a packet should be
dropped because of redundancy by identifying the flow identification
and sequence number.
4.3. Control Plane Considerations
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(1) +----------+
+------------------->+Controller|
| +----+-----+
|(2) / \
| +---------------/-----\-----------------+
| | / (3) \ |
+--V-------+ +--------V-+-->+-----V----+ +----------+
| Ingress +--|Relay Node| |Relay Node|-->| Egresss |
+----------+ +----------+-->+----------+ +----------+
| Replication Elimiantion |
+---------------------------------------+
DetNet Domain
1. Edge node->Controller: Sends a path computation requirement
containing that service protection in order to have ultra-reliability
through PCEP/BGP extenisons.
2. Controller->Edge node: Computes a P2MP2P path, including
replication nodes and elimination nodes. Between a pair of
replication node and elimination node, there are more than one path,
and if any equipment failure happens in one of them, the DetNet
service is not interrupted. Send the path computation result to the
edge node through PCEP/BGP extensions.
3. Controller->Relay Node : In a P2MP2P path, every pair of
replication node and elimination node should be configured to
identify different DetNet flows by the different flow
identifications, and the rule of sequence number should be negotiated
between relay nodes. After replication or elimination, the explicit
path to the next relay is also required through BGP extensions or
Netconf YANG.
5. Resource Reservation
5.1. Resource Reservation Scenarios
The figure below shows that an IPv6 flow is sent out from the end
station E1. The packet of the flow is encapsulated in an outer
IPv6+SRH header as a DetNet SRv6 packet in the Ingress(In) and
transported through an SRv6 DetNet domain. In the Egress(Eg), the
outer IPv6 header+SRH of the packet is popped, and the packet is sent
to the destination E2.
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| |
----IPv6--->|<---------------SRv6 DetNet------------->|<----IPv6---
| |
| |
+---+ +---+ +---+ +---+
| E1+----| In|--+T1+---------+T2+---------+T3+----| Eg+----+ E2|
+---+ +---+ +---+ +---+
The DetNet packet processing is as follows:
Ingress:
Inserts the SRv6 Policy that will steer the packet from Ingress to
the destination.
The methods and mechanisms used for defining, instantiating and
applying the policy are outside of this document. An example of
policies are described in [I-D.ietf-spring-segment-routing-policy]
Explicit route and the corresponding resource is carried in the
SRH.
T1 Node (Transit Node):
Forward the packet with the allocated resource.
This is a new function in the context of SRv6 Network Programming
which will associate a given SID to a replication instruction in
the node originating and advertising the SID. The instruction
includes:
* Forward the packet to the link bound to the SID
* Use the resource when forwarding the packet
The processing of T2 and T3 Node is similar.
Egress:
Decapsulates the outer IPv6 header.
Sends the inter packet to the End Station 2.
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5.2. Data Plane Considerations
Congestion could cause uncontrolled delay and packet loss. DetNet
flows are supposed to be protected from congestion, so enough
resource reservation for DetNet service is necessary. Some of the
resource in the network is complex and hard to quantize, e.g., packet
processing resource; while some of them is easy to get and calculate,
e.g., buffer size, port bandwidth and so on. In order to use the
allocated resource for the DetNet flow, SRv6 for DetNet is supposed
to carry the information of the resource. And the network device
could transit the packet following the instruction in the SRH with
the corresponding resources.
5.3. Control Plane Considerations
(1) +----------+
+------------------->+Controller|
| +----+-----+
|(2) / \
| +---------------/-----\-------------------+
| | / (3) \ |
+--V-------+ +--------V---+ +---V--------+ +----------+
| Ingress +--|Transit Node|---|Transit Node|-->| Egress |
+----------+ +------------+ +------------+ +----------+
| Resource Reservation |
+------------------------------------------+
DetNet Domain
1. Edge node->Controller: Sends a path computation requirement
containing the flow characteristics and resource reservation request
through BGP/PCEP.
2. Controller->Edge node: The controller should collect the network
resource information of the network, e.g., bandwidth, buffer size and
so on, and maintain the resource status for every device/output port.
Based on the flow characteristics, the controller should find a path
which can guarantee that there are enough resources in every device/
output port the flow goes through. The controller sends the path
computation results back to the edge node, and update the resources
status of the network through BGP/PCEP.
3. Controller->Transit Node: Every transit node along the path
should be configured in order to make sure that when the DetNet flow
goes through, the allocated resource for this flow is able to be used
and no more resource than what is allocated will be used for the same
flow through BGP/Netconf YANG.\
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6. Explicit Route
SRv6 could support explicit route using segment list without extra
extension. In DetNet, explicit route could be used with service
protection or resource reservation. When explicit route works with
service protection, a P2MP2P path is required to indicate the
behavior of replication and elimination. When explicit route works
with resource reservation, the explicit path indicates the nodes or
links a DetNet flow goes through, and also indicates the resource
allocated for the DetNet flow in the specified nodes or links.
7. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Security Considerations
TBD
9. Acknowledgements
Thank you for valuable comments from James Guichard and Andrew Mails.
10. Normative References
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-filsfils-spring-srv6-network-
programming-07 (work in progress), February 2019.
[]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), October 2019.
[I-D.ietf-detnet-dp-sol-mpls]
Korhonen, J. and B. Varga, "DetNet MPLS Data Plane
Encapsulation", draft-ietf-detnet-dp-sol-mpls-02 (work in
progress), March 2019.
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[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-07 (work in progress),
May 2020.
[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>.
[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>.
[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>.
[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>.
Authors' Addresses
Xuesong Geng
Huawei
Email: gengxuesong@huawei.com
Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
Mach Chen
Huawei
Email: mach.chen@huawei.com
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