Best practices for traffic steering to SRv6
draft-geng-srv6ops-traffic-steering-to-srv6-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Gary Geng , Yisong Liu , Chongfeng Xie , Changwang Lin | ||
| Last updated | 2024-03-04 | ||
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draft-geng-srv6ops-traffic-steering-to-srv6-00
Network Working Group Gary Geng
Internet Draft Tencent
Intended status: Informational Y. Liu
Expires: September 3, 2024 China Mobile
C. Xie
China Telecom
C. Lin
New H3C Technologies
March 4, 2024
Best practices for traffic steering to SRv6
draft-geng-srv6ops-traffic-steering-to-srv6-00
Abstract
This document primarily describes the traffic steering towards SRv6-
BE and SRv6-TE respectively, providing an overview of the main
traffic steering methods for these two approaches. Furthermore, it
discusses the recommended traffic steering methods for various
typical scenarios.
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 September 3, 2024.
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Table of Contents
1. Introduction...................................................3
1.1. Conventions and Terminology...............................3
2. Steering to SRv6...............................................3
2.1. Steering to SRv6 based on destination address.............3
2.2. Steering to SRv6 based on flow characteristics............5
3. UseCase........................................................6
3.1. Traffic steering based on destination address.............7
3.1.1. BSID-based Traffic Steering..........................7
3.1.2. Color-based Traffic Steering ........................7
3.1.3. IGP-Shortcut Traffic Steering .......................7
3.2. Traffic steering based on flow characteristics............8
3.2.1. Dscp-based Traffic Steering .........................8
3.2.2. 802.1p-based Traffic Steering........................8
3.2.3. Service-class-based Traffic Steering.................9
3.2.4. Te-class-based Traffic Steering .....................9
3.2.5. Traffic steering via BGP-FlowSpec ..................10
4. Security Considerations.......................................11
5. IANA Considerations...........................................11
6. References....................................................11
6.1. Normative References ....................................11
Authors' Addresses...............................................12
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1. Introduction
The general purpose of traffic steering is to optimize the
allocation and transmission of network resources, ensure a balanced
distribution of network traffic, improve network performance, reduce
congestion, and increase available bandwidth to provide users with a
better network experience.
This document initially describes the traffic steering towards SRv6-
BE and SRv6-TE respectively, and outlines the main traffic steering
methods for these two approaches. Finally, it discusses the
recommended traffic steering methods for various typical scenarios.
1.1. Conventions and Terminology
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. Steering to SRv6
Steering to SRv6 can be categorized into two types: Steering based
on destination address and Steering based on flow characteristics.
The means of traffic steering in SRv6 include using static routing
for traffic steering, employing PBR (Policy-Based Routing) policies
for traffic steering, distributing routes through BGP (Border
Gateway Protocol) for traffic steering, utilizing BGP-Flowspec to
publish rules for traffic steering, and utilizing IGP-Shortcut for
traffic steering.
2.1. Steering to SRv6 based on destination address
Traffic can typically be steered based on the destination address by
matching traffic destination address via static routing or utilizing
Policy-Based Routing (PBR).
1)Steering traffic to SRv6 via static routing:
ipv6 route-static {x:x::x:x/xx} {y:y::y:y}
Steering traffic based on the destination address with static
routing.
Where {y:y::y:y} represents an SRv6 SID, which can be a DT4/DT6
address, indicating traffic steering into an L3VPN;
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If {y:y::y:y} is a BSID address, it represents traffic steering into
an SRv6 TE Policy;
ipv6 route-static {x:x::x:x/xx} color {color} end-point ipv6 {end-
point}
Through the above static route configuration, for matched
destination addresses, traffic color and end-point can be specified,
and associated with an SRv6 TE Policy, enabling traffic steering
into the SRv6 TE Policy.
2) Steering traffic to SRv6 via PBR:
ipv6 policy-based-route srv6 permit node 0
if-match acl 2000
apply next-hop y:y::y:y
Steering traffic based on the destination address using PBR.
Similarly, if {y:y::y:y} represents a DT4/DT6 address, it indicates
traffic steering into an L3VPN;
If {y:y::y:y} is a BSID address, it signifies traffic steering into
an SRv6 TE Policy;
When using PBR for traffic steering, for matched destination
addresses, specifying traffic color and end-point, and associating
with an SRv6 TE Policy, can effectively steer traffic into the SRv6
TE Policy.
3) Steering traffic to SRv6 via BGP-FlowSpec:
By deploying BGP-FlowSpec rules from the controller, traffic
matching specific destination addresses can be steered.
Once matched, BGP-FlowSpec can specify the next-hop address as a
DT4/DT6 address to route the traffic into an L3VPN. Alternatively,
specifying the next-hop address as a BSID address can direct the
traffic into an SRv6 TE Policy.
4) Steering traffic to SRv6 via IGP shortcut:
IGP shortcut, also known as the automatic traffic announcement
feature of an IGP, treats an SRv6 TE Policy as a direct link between
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the endpoints for announcement purposes. During route calculation,
if the destination address of the traffic corresponds to the
tunnel's destination address, the traffic is steered into the SRv6
TE Policy.
2.2. Steering to SRv6 based on flow characteristics
Identifying traffic based on specific flow characteristics and
steering traffic according to these characteristics. Flow
characteristics include Layer 2 attribute 802.1p, Layer 3 IP feature
DSCP value, as well as service-level attributes such as service
class and TE class ID.
1) Steering Traffic to SRv6 via PBR Based on Traffic Characteristics
ipv6 policy-based-route srv6 permit node 0
if-match acl 2000
apply next-hop y:y::y:y
#
By specifying traffic characteristics in the ACL to match traffic
and then designating the next-hop for the traffic as the SRv6 next-
hop address or BSID address, traffic can be directed to SRv6 BE or
SRv6 TE policy.
2)Steering traffic via BGP flowspec
By using flowspec, specify the next-hop address in the route
attributes as the BSID of the SRv6 TE Policy, in order to steering
the traffic associated with this route to the destination of the
SRv6 TE Policy.
By using flowspec, specify the next-hop address in the route
attributes as the BSID of the SRv6 TE Policy, in order to steering
the traffic associated with this route to the destination of the
SRv6 TE Policy.
3) Steering to SRv6 TE via Tunnel-Policy
First, based on the traffic destination address, tunnel policies are
matched and associated with an SRv6 TE Policy-Group. The Policy-
Group contains multiple policies, each with a different color value.
A specific traffic characteristic is then mapped to different color
values, and based on the color value, corresponding SR Policies are
found within the Policy-Group to direct the traffic to the SR TE
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Policy. Typically, the characteristics used to map traffic to
different colors include DSCP values, Dot1P values, TE Class IDs,
service classes, and others.
3. UseCase
SRv6 BE(Best Effort), is a method of forwarding traffic without
strict quality of service guarantees. It allows for the flexible and
efficient forwarding of packets, prioritizing simplicity and
scalability. This approach is well-suited for scenarios where fine-
grained traffic control is not necessary and where best effort
delivery meets the requirements of the network.
Traffic engineering technology calculates and arranges the
forwarding paths of traffic to optimize network resource utilization
and improve bandwidth efficiency. Additionally, this technology
ensures reliable service quality for business operations and
prevents all business traffic from competing for resources on the
shortest path. Therefore, deploying and utilizing traffic
engineering in SRv6 networks has become a necessary requirement for
the promotion and development of SRv6 technology.
The traffic engineering technology based on SRv6 is referred to as
SRv6 TE.
As shown in Figure 1, SRv6 Policy 1 has a BSID of 1000::1, Color
100, and Endpoint 4::4, with a forwarding path of B->C->D. SRv6
Policy 2 has a BSID of 2000::1, Color 200, and Endpoint 4::4, with a
forwarding path of E->F->D.
SRv6 Policy 1: +---------+ +---------+
BSID<1000::1> |RouterB |--------------------|RouterC |
Color 100 +-/-------+ +-------\-+
Endpoint 4::4 / \
SID List<B,C,D> / \
+-/------+ BGP Route +------\-+
|RouterA | <---------------- |RouterD | EndPoint: 4::4
+-\------+ +------/-+
SRv6 Policy 2: \ /
BSID<2000::1> \ /
Color 200 +-\-------+ +-------/-+
Endpoint 4::4 |RouterE |--------------------|RouterF |
SID List<E,F,D> +---------+ +---------+
Figure 1. SRv6 Traffic Steering Network Diagram
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3.1. Traffic steering based on destination address
3.1.1. BSID-based Traffic Steering
When a device receives a packet with a destination IPv6 address
matching the BSID of an SRv6 TE Policy, the packet will be forwarded
according to the corresponding SRv6 TE Policy. BSID-based traffic
steering is commonly used in BSID stitching scenarios, where the
BSID of another SRv6 TE Policy is added to the SID list of one SRv6
TE Policy. This helps reduce the length of the SRH header in the
packet during the forwarding process, enabling seamless stitching
between different SRv6 TE Policies or between an SRv6 TE Policy and
an SR-MPLS TE Policy.
As shown in Figure 1, when the destination address of traffic is
specified as BSID 1000::1 of SRv6 Policy 1, the traffic will be
forwarded along the path defined by SRv6 TE Policy 1. If the
destination address is specified as BSID 2000::1 of SRv6 Policy 2,
the traffic will be forwarded along the path defined by SRv6 TE
Policy 2.
3.1.2. Color-based Traffic Steering
Color-based traffic steering is one of the fundamental methods used
in SRv6 TE Policy. This approach leverages the BGP route's extended
community attribute called Color and the destination address to
match the Color and End-point address in the SRv6 TE Policy.
Typically, if there is an SRv6 TE Policy on the device with the same
Color and End-point address as the Color extended community
attribute and next-hop address of the BGP route, the BGP route will
be steered to that SRv6 TE Policy. When the device receives a packet
that matches the BGP route, it is forwarded through the SRv6 TE
Policy.
As shown in Figure 1, the BGP protocol advertises the prefix routes
that require traffic steering, such as specifying the Color
attribute of route 1::1/128 as 100 and the next-hop attribute as
4::4, and specifying the Color attribute of route 2::2/128 as 200
and the next-hop attribute as 4::4. Therefore, for traffic with a
destination address of 1::1, it will be forwarded along the path
defined by SRv6 TE Policy 1, while for traffic with a destination
address of 2::2, it will be forwarded along the path defined by SRv6
TE Policy 2.
3.1.3. IGP-Shortcut Traffic Steering
When using IGP-shortcut for traffic steering based on the
destination address, the routing table information for traffic
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steering is no longer published by the BGP protocol. Instead, it is
automatically generated on the head-end device A based on the SRv6
TE Policy. In the scenario illustrated in Figure 1, enabling the
IGP-shortcut feature causes the head-end node to automatically
generate a route for 4::4/128 and set the egress interface to point
to the SRv6 TE Policy when the SRv6 TE Policy status is Up. In the
event that the SRv6 TE Policy status changes to Down, the
automatically generated route pointing to the SRv6 TE Policy is
withdrawn and replaced with forwarding based on SRv6 BE.
3.2. Traffic steering based on flow characteristics
3.2.1. Dscp-based Traffic Steering
The basic principle of DSCP-based traffic steering is to route the
packets to the corresponding SRv6 TE Policy based on the DSCP
(Differentiated Services Code Point) value of the packet. This
traffic steering method requires the deployment of SRv6 TE Policy
groups and the redirection of traffic to these SRv6 TE Policy
groups. After that, specific DSCP values are mapped to corresponding
SRv6 TE Policy groups to steer the packets to the desired SRv6 TE
Policy.
As shown in Figure 1, the BGP protocol advertises the prefix routes
that require traffic steering, specifying the next-hop attribute of
route 1::1/128 as 4::4 but not specifying the Color attribute. On
device A, an SRv6 TE Policy group is created with an End-point
address of device D's address 4::4. Within the SRv6 TE Policy group,
a Color and DSCP mapping relationship is defined, where DSCP 10 maps
to Color 100 and DSCP 20 maps to Color 200. Subsequently, a tunnel
policy is configured on source node A, binding the SRv6 TE Policy
group with the destination address 2.2.2.2. This arrangement ensures
that for traffic with a destination address of 1::1, if the DSCP
value is 10, it will be forwarded along the path defined by SRv6 TE
Policy 1; if the DSCP value is 20, it will be forwarded along the
path defined by SRv6 TE Policy 2.
3.2.2. 802.1p-based Traffic Steering
The basic principle of 802.1p-based traffic steering is to route the
packets to the corresponding SRv6 TE Policy based on the 802.1p
(Priority) value of the packet. This traffic steering method
requires the prior deployment of SRv6 TE Policy groups and the
redirection of traffic to these SRv6 TE Policy groups. Subsequently,
based on the mapping rules within the SRv6 TE Policy groups, packets
with specific 802.1p values are steered to the corresponding SRv6 TE
Policy.
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As shown in Figure 1, the BGP protocol advertises the prefix routes
that require traffic steering, specifying the next-hop attribute of
route 1::1/128 as 4::4 but not specifying the Color attribute. On
device A, an SRv6 TE Policy group is created with an End-point
address of device D's address 4::4. Within the SRv6 TE Policy group,
a Color and 802.1p mapping relationship is defined, where 802.1p 10
maps to Color 100 and 802.1p 20 maps to Color 200. Subsequently, a
tunnel policy is configured on source node A, binding the SRv6 TE
Policy group with the destination address 2.2.2.2. This setup
ensures that for traffic with a destination address of 1::1, if the
802.1p value is 10, it will be forwarded along the path defined by
SRv6 TE Policy 1; if the 802.1p value is 20, it will be forwarded
along the path defined by SRv6 TE Policy 2.
3.2.3. Service-class-based Traffic Steering
To ensure that all traffic packets can be steered, even if they do
not carry DSCP or Dot1p information, the device introduces a local
identification called "service-class" to distinguish different
classes of service traffic.
Both service-class-based traffic steering and CBTS-based traffic
steering are achieved through the service-class identifier. However,
service-class-based traffic steering requires the traffic to first
enter the SRv6 TE Policy group, and then, based on the mapping rules
within the SRv6 TE Policy group, specific packets with service-class
identifiers are redirected to the corresponding SRv6 TE Policy.
As shown in Figure 1, the BGP protocol advertises the prefix routes
that require traffic steering, specifying the next-hop attribute of
route 1::1/128 as 4::4 but not specifying the Color attribute. On
device A, an SRv6 TE Policy group is created with an End-point
address of device D's address 4::4. Within the SRv6 TE Policy group,
a Color and service-class mapping relationship is defined, where
service-class 1 maps to Color 100 and service-class 2 maps to Color
200. Subsequently, a tunnel policy is configured on source node A,
binding the SRv6 TE Policy group with the destination address
2.2.2.2. This setup ensures that for traffic with a destination
address of 1::1, if the service-class value is 1, it will be
forwarded along the path defined by SRv6 TE Policy 1; if the
service-class value is 2, it will be forwarded along the path
defined by SRv6 TE Policy 2.
3.2.4. Te-class-based Traffic Steering
Due to the limited length of the local identifier "service-class,"
with the maximum supported value for most devices being 15 and
typically not exceeding 127, it cannot effectively differentiate a
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vast number of services. Therefore, H3C has introduced the use of
"TE class ID" as another local identifier. The TE class ID can have
a maximum value of 65535, supporting a more diverse range of traffic
types.
The basic principle of TE class ID-based traffic steering is to
route the packets to the corresponding SRv6 TE Policy based on the
TE class ID identifier. This traffic steering method requires the
prior deployment of SRv6 TE Policy groups and the redirection of
traffic to these SRv6 TE Policy groups. Then, based on the mapping
rules within the SRv6 TE Policy groups, packets marked with specific
TE class ID values are steered to the corresponding SRv6 TE Policy.
As shown in Figure 1, the BGP protocol advertises the prefix routes
that require traffic steering, specifying the next-hop attribute of
route 1::1/128 as 4::4 but not specifying the Color attribute. On
device A, an SRv6 TE Policy group is created with an End-point
address of device D's address 4::4. Within the SRv6 TE Policy group,
a te-class and service-class mapping relationship is defined, where
te-class 1 maps to Color 100 and te-class 2 maps to Color 200.
Subsequently, a tunnel policy is configured on source node A,
binding the SRv6 TE Policy group with the destination address
2.2.2.2. This setup ensures that for traffic with a destination
address of 1::1, if the te-class value is 1, it will be forwarded
along the path defined by SRv6 TE Policy 1; if the te-class value is
2, it will be forwarded along the path defined by SRv6 TE Policy 2.
3.2.5. Traffic steering via BGP-FlowSpec
In the scenario illustrated in Figure 2, where a controller is
present in the network, fine-grained traffic scheduling can be
achieved by the controller distributing traffic steering rules. The
controller utilizes BGP Flow-Spec (FS) to distribute rules to the
head-end node. These rules can be matched based on the destination
address or flow characteristics. By setting the action after
matching, the controller can specify the Color attribute and next-
hop address for the traffic, thereby achieving traffic steering. BGP
FlowSpec enables global traffic scheduling with flexibility.
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+------------------+
| Controller |
+------------------+
| FlowSpec route to Ingress:
| NLRI: Filter Rules
FS Color: 100/200
| Nexthop: 4::4
SRv6 Policy 1: +---------+ | +---------+
BSID<1000::1> |RouterB |------)-------------|RouterC |
Color 100 +-/-------+ | +-------\-+
Endpoint 4::4 / | \
SID List<B,C,D> / | \
+-/------+ | +------\-+
|RouterA | <--------+ |RouterD | EndPoint: 4::4
+-\------+ +------/-+
SRv6 Policy 2: \ /
BSID<2000::1> \ /
Color 200 +-\-------+ +-------/-+
Endpoint 4::4 |RouterE |--------------------|RouterF |
SID List<E,F,D> +---------+ +---------+
Figure . Steering by BGP FlowSpec
4. Security Considerations
TBD.
5. IANA Considerations
This document makes no request of IANA.
6. References
6.1. Normative References
[rfc9256] C. Filsfils, "Segment Routing Policy Architecture ", July
2022, <https://datatracker.ietf.org/doc/rfc9256>
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Authors' Addresses
Gary Geng
Tencent
China
Email: garygeng@tencent.com
Yisong Liu
China Mobile
China
Email: liuyisong@chinamobile.com
Chongfeng Xie
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: xiechf@chinatelecom.cn
Changwang Lin
New H3C Technologies
Beijing
102209
China
Email: linchangwang.04414@h3c.com
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