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

[RFC9657] introduces a set of use cases where the topology of the network changes predictably. 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. However, on a network with predictable topology changes, the ingress node knows future topology changes, it can schedule the forwarding paths in advance, and steer flows to different set of paths based on time to prevent packet forwarding from being affected by topology changes.¶

This document extends BGP Flow Specification with scheduling time information to identify the packets arrived at different time slot. Based on that, the headend can perform different actions at different time for the same traffic.¶

2. Motivation

[RFC9657] introduces the time variant network use cases, the tidal network is one of the typical time variant network scenarios. In the tidal network, 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 controller can generate a FlowSpec with scheduling time rule to identify the packets arriving time and corresponding paths. The headend doesn't need to wait for the advertisement of topology change and just steer traffic in to different paths based on the flowSpec with scheduling time information, the affection of topology change is minimized.¶

3. Scheduling Time Information in FlowSpecv1

[RFC8955] defines 12 Components to identify different traffics. Based on [RFC8955], this document defines a new Component to identify the arrival time of packets and perform different actions.¶

Encoding: <type (1 octet, TBD1), length (1 octet), scheduling time information (variable)+>¶

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

4. Scheduling time information in FlowSpecv2

[I-D.ietf-idr-flowspec-v2] specifies BGP flow specification v2(FSv2) to address the issues detected during the deployment of BGP flow specification v1. It defines that the traffic filters are described in the format of sub-TLV and different traffic type have different filter sub-TLVs.¶

For the IP and VPN IP filters, FSv2 reused the components defined in [RFC8955], [RFC8956], and [I-D.ietf-idr-flowspec-srv6]. Therefore, the new component defined for FlowSpecv1 in Section 3 is also applicable for FlowSpecv2¶

For L2 Traffic, this document defines a new sub-TLV for L2 filters defined in Section 3 of [I-D.ietf-idr-flowspec-v2] to identify the arrival time of packets and perform different actions. The format of Scheduling Time sub-TLV is shown as follows:¶

 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      |     Length    |   Reserved    |Schedule Number|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
/                Scheduling Time Information                    /
|                                                               |

Type: TBD2¶

Length: the size of the value field in octets, variable.¶

Schedule Number: indicates the number of schedules.¶

Schedules Time information: one or more schedules, each schedule indicates when one or more time slots.¶

5. Scheduling Time Information

The format of Scheduling time information sub-TLV is shown as follows:¶

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Schedule-id  |    Priority   |    Reserved   |   Flags   |P|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Start Time                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Start Time                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      End Time (Duration)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      End Time (Duration)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Frequency (Optional)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   Recurrence count(Optional)                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Schedule-id: 8-bit value, the unique identifier to distinguish each schedule within a FlowSpec, this value is allocated by the FlowSpec generator.¶

Priority: 8-bit value, this field is used when there are multiple schedules valid at the same point. The higher value indicates higher priority and the default Preference value is 10.¶

Flags: 8 bits, currently only 2 bits are used, the other bits are reserved.¶

P (Period format): one-bit flag to indicate the format of a period. if P=1, then the period is described by a start time filed and an end time field; If P =0, then the period is described by a start time field and a duration time field.¶

S (Schedule type): one-bit flag to indicate the type of a schedule. If S=0, it indicates the schedule only has one instance, the Frequency and Recurrence count field should not be included in the sub-TLV; If S=1, it indicates the schedule has multiple instances, the Frequency and Recurrence count field should be included.¶

Start Time: 64-bit value, the number of seconds since the epoch, it indicates when the FlowSpec start to take effect.¶

End Time (Duration): 64-bit value, if the flag P=1, then it is the number of seconds since the epoch, it indicates when the FlowSpec becomes ineffective. If the flag P=0, then it is the number of seconds since the Start Time, it indicates how long the FlowSpec take effect.¶

Frequency(optional): 32-bit value, it is the numbers of seconds since the Start Time of an instance to the Start Time of next instance. This field indicates the recurrence frequency for all the instance of this schedule. This field should not be included if S=0.¶

Recurrence Count(optional): 32-bit value, it indicates the number of occurrences. For example, if it is set to 2, then the schedule will repeat twice with the specified Frequency. This field should not be included if P=0.¶

6. Security Considerations

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

7. IANA Considerations

IANA is requested to allocate a new type value for "Scheduling Time Information" Component in "Flow Spec Component Types" registry:¶

IANA is requested to allocate a new type value for "Scheduling Time sub-TLV" in "L2 Flow Specification Component Types" registry[I-D.ietf-idr-flowspec-l2vpn]:¶

8. References

Authors' Addresses