BGP Flow Specification Extensions for Path Scheduling

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Table of Contents

1. Introduction

[RFC8955] and [RFC8956] define the BGP [RFC4271] Flow Specification (FlowSpec) that allows conveying flow specifications and traffic Action/Rules associated. BGP Flow specifications are encoded within the MP_REACH_NLRI and MP_UNREACH_NLRI attributes [RFC4760]. Rules (Actions associated) are encoded in Extended Community attribute [RFC4360]. The BGP Flow Specification function allows BGP Flow Specification routes that carry traffic policies to be transmitted to BGP Flow Specification peers to steer traffic.¶

[I-D.ietf-idr-ts-flowspec-srv6-policy] describes BGP flow specification usage that are used to steer data flow into an SR Policy which can steer traffic into a specific path.¶

The existing traffic filter rules and actions in FlowSpec are always effective and will steer specific traffic into one Policy once been delivered to the headend. However, there are many scenarios that need to schedule routing paths in the network.¶

[I-D.zzd-tvr-use-case-tidal-network] introduces the tidal network, in which the topology of the network will change periodically over time. The topology change may cause some of the paths invalid, and lead to path reselection or even recalculation. However, the reselection or recalculation takes a period of time, which will affect packet forwarding and cause problems such as packet disorder and packet loss. On a network with predictable topology changes, the controller knows future topology changes, it can deliver several policies for different topology to the headend in advance. Then the headend steers traffic to different policies based on time to prevent packet forwarding from being affected by topology changes.¶

This document defines a new type of component for BGP Flow Specification to identify the packets arrived at different time slot. Based on that, the headend can steer packets into different paths at different time.¶

2. Motivation

[I-D.zzd-tvr-use-case-tidal-network] introduces the time variant routing scenario in the tidal network, in which the traffic volume varies greatly at different time. In order to reduce the power consumption, some of the links and nodes may be shut down when the traffic is at a low level.¶

In this scenario, the SR policy originator can generate several policies for different topologies. The headend doesn’t need to wait for the advertisement of topology change and just steer traffic in to different policies based on the flowSpec with scheduling time information, the affection of topology change is minimized.¶

3. Scheduling time information in FlowSpec

[RFC8955] defines 12 Components to identify different traffics. Based on [RFC8955], this document defines a new Component to identify the arrival time of packets, so as to enable Policies scheduling.¶

Encoding: <type (1 octet), length (1 octet), scheduling time information (variabile)]+>¶

Defines the time information that matches the arrival time of packets. This component matches if either the arrival time of an IP packet in the scope of scheduling time information.¶

The Scheduling time information has two formats according to the change regularity of network topology. They are Aperiodic Scheduling Time Information (ASTI) and Periodic Scheduling Time Information (PSTI).¶

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Enable Time                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Disable Time                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
/                          Variable                             /
|                                                               |

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            Period                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Enable Time                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Disable Time                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
/                          Variable                             /
|                                                               |

4. Procedures

When the headend device (as a FlowSpec client) receives a instruction with scheduling time information from a BGP FlowSpec Controller, it will steer the traffic packets matching the time slot and other conditions in the Flowspec instruction into a specific Policy.¶

And the packets will be encapsulated with an SR List <S1, S2, S3> in the headend device, then send the packets to the TailEnd device along the path indicated by the SR list.¶

5. Security Considerations

These extensions to BGP FlowSpec do not add any new security issues to the existing protocol.¶

6. IANA Considerations

This document defines a new Component in the registry " Flow Spec Component Types" to be assigned by IANA:¶

Authors' Addresses