BGP SR Policy Extensions for Path Scheduling
draft-zzd-idr-sr-policy-scheduling-06
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Li Zhang , Tianran Zhou , Jie Dong , Minxue Wang , Nkosinathi Nzima | ||
| Last updated | 2024-10-21 | ||
| RFC stream | (None) | ||
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draft-zzd-idr-sr-policy-scheduling-06
IDR L. Zhang, Ed.
Internet-Draft T. Zhou
Intended status: Standards Track J. Dong
Expires: 24 April 2025 Huawei
M. Wang
China Mobile
N. Nzima
MTN
21 October 2024
BGP SR Policy Extensions for Path Scheduling
draft-zzd-idr-sr-policy-scheduling-06
Abstract
Segment Routing (SR) policy enables instantiation of an ordered list
of segments with a specific intent for traffic steering. However,
more and more cases require path scheduling to improve the network
availability and resource utilization.
This document proposes extensions to BGP SR Policy to indicate the
scheduling time of each candidate path(segment list) and its
associated attributes.
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 24 April 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Tidal Network Use Case . . . . . . . . . . . . . . . . . 3
2.2. Resource utilization efficiency use case . . . . . . . . 4
3. Scheduling Time Information in SR Policy . . . . . . . . . . 4
4. Scheduling Time Information Sub-TLV . . . . . . . . . . . . . 6
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Segment Routing (SR) policy [RFC9256] is a set of candidate SR paths
consisting of one or more segment lists and necessary path
attributes. It enables instantiation of an ordered list of segments
with a specific intent for traffic steering.
[I-D.ietf-idr-segment-routing-te-policy] specifies how BGP may be
used to distribute SR Policy candidate paths. It introduces a BGP
SAFI with new NLRI to advertise a candidate path of a Segment Routing
(SR) Policy.
In tidal network, the topology of the network will change
periodically over time to reduce energy consumption[RFC9657]. 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. Therefor, some actions should be token to requece the impact
of predicted topology changes.
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[RFC8934] extends the stateful PCE Communication Protocol (PCEP) to
enable Label Switched Path (LSP) path computation, activation, setup,
and deletion based on scheduled time intervals for the LSP and the
actual network resource usage in a centralized network environment so
as to improve the resource utilization efficiency. Similar with
[RFC8934], in the scenario of SR-policy-based TE paths, the resource
allocation efficiency is a big challenge. Some flows just last for a
short time, but the TE paths resources for the flows are usually
reserved for a long time and can not be used by other services.
In order to solve these problesm, this document proposes extensions
to BGP SR Policy to indicate the scheduling time of each candidate
path(segment list) and its associated attributes. The policy
originator can deliver multiple paths with different valid time to
the headend. The headend determines the current valid paths based on
the arrival time of the packet and forwards along the path.
1.1. Requirements Language
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. Motivation
This section describes the use cases that may benefit from scheduled
paths.
2.1. Tidal Network Use Case
[RFC9657] introduces the time variant network use cases, the tidal
network is one of the typical time variant network scenarios. In the
tidal network, in which the traffic volume varies greatly at
different time.
In the tidal network, some links and nodes are shutdown when the
traffic at a low level. In this case, the availability of nodes and
links will affect the forwarding path of traffic, the packet loss
will occur if the headend can’t react to these changes in time.
Therefore, the scheduling time information of each candidate path or
segment list can be added to the SR Policy to describe the valid
period. The ingress node doesn’t need to wait for the advertisement
of topology change and just changes the forwarding path based on the
valid time of each path, the affection of topology change is
minimized.
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2.2. Resource utilization efficiency use case
Traditionally, the usage and allocation of network resources,
especially bandwidth, can be supported by a Network Management System
(NMS) operation such as path pre-establishment. However, this may
not provide efficient usage of network resources. The established
paths may reserve the resources for a long time. During this period,
the resources cannot be used by other services even when they are not
used for transporting any service.
In the scenario of SR-policy-based TE path, the resource allocation
efficiency is also a problem. Some flows just last for a short
period of time, but the TE paths resources for the flows are usually
reserved for a long time and cannot be used by other services.
Therefore, the scheduling time information of each candidate path or
segment list can be added to the SR Policy to describe the
valid(invalid) period. When the TE path is invalid, the ingress node
does not steer any packets to the path and releases the resources.
Furthermore, the controller can use the resource released by the flow
to plan TE paths for other flows that do not have overlap time, which
can effectively improve the utilization of network resources.
3. Scheduling Time Information in SR Policy
The NLRI defined in [I-D.ietf-idr-segment-routing-te-policy] contains
the SR Policy candidate path. The content of the SR Policy Candidate
Path is encoded in the Tunnel Encapsulation Attribute defined in
[RFC9012] using a new Tunnel-Type called SR Policy Type with
codepoint 15. The SR Policy encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encapsulation Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
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A candidate path includes multiple SR paths, each of which is
specified by a segment list. The Scheduling time information can be
applied to the candidate path, to indicate the valid time for each
candidate path and its associated attributes. The new SR Policy
encoding structure is expressed as below:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encapsulation Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Scheduling Time Information
Segment List
Weight
Segment
Segment
...
...
The Scheduling time information also can be applied to each segment
list to indicate the valid time for each segment list and its
associated attributes. The new SR Policy encoding structure is
expressed as below:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encapsulation Attribute (23)
Tunnel Type: SR Policy (15)
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Scheduling Time Information
Weight
Segment
Segment
...
...
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4. Scheduling Time Information Sub-TLV
The Scheduling time information sub-TLV indicates one or more valid
time slot for one or more SR paths. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |Schedule Number|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ Schedules /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Scheduling Time Information Sub-TL
Type: TBD1
Length: the size of the value field in octets.
Schedule Number: indicates the number of schedules.
Schedules: one or more schedules, each schedule indicates the
duration when the candidate path(segment list) is active. The format
of each schedule 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 | Flags |P|S| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End Time (Duration) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End Time (Duration) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frequency (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Recurrence count(Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Schedule of SR Policy
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Schedule-id: 8-bit value, the unique identifier to distinguish each
schedule within a SR Policy, this value is allocated by the SR Policy
generator.
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 candidate path (segment list) and its associated
attributes 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 candidate
path (segment list) and its associated attributes becomes
ineffective. If the flag P=0, then it is the number of seconds since
the Start Time, it indicates how long the candidate path (segment
list) and its associated attributes are effective.
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.
5. Procedures
When a SR Policy head node receives a SR Policy with scheduling time
information, the head node will parse the SR Policy and save the
scheduling time information locally. When a data packet arrives, the
head node will steer it to a specific SR Policy by color or other
means.
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Within a specific SR Policy, there are two ways for the head node to
determine the final forwarding SR path:
Option 1: A valid SR path is dynamically determined based on the
packet arrival time whenever a packet arrives.
Option 2: One or more valid paths are selected for the SR policy and
one or more timers are set based on the path disable time. When the
timer expires, packets steered to this SR policy are switched to
another path.
6. Security Considerations
These extensions to BGP SR Policy do not add any new security issues
to the existing protocol.
7. IANA Considerations
This document defines two new sub-TLV in the registry "BGP Tunnel
Encapsulation Attribute sub-TLVs" to be assigned by IANA:
+=======+===========================================+===============+
| Value | Description | Reference |
+=======+===========================================+===============+
| TBD1 | Scheduling Time Information (STI) sub-TLV | This |
| | | document |
+-------+-------------------------------------------+---------------+
Table 1
8. References
8.1. Normative References
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-segment-
routing-te-policy-26, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-26>.
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[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[RFC9657] Birrane III, E., Kuhn, N., Qu, Y., Taylor, R., and L.
Zhang, "Time-Variant Routing (TVR) Use Cases", RFC 9657,
DOI 10.17487/RFC9657, October 2024,
<https://www.rfc-editor.org/info/rfc9657>.
[RFC8934] Chen, H., Ed., Zhuang, Y., Ed., Wu, Q., and D. Ceccarelli,
"PCE Communication Protocol (PCEP) Extensions for Label
Switched Path (LSP) Scheduling with Stateful PCE",
RFC 8934, DOI 10.17487/RFC8934, October 2020,
<https://www.rfc-editor.org/info/rfc8934>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
Authors' Addresses
Li Zhang (editor)
Huawei
Beiqing Road
Beijing
China
Email: zhangli344@huawei.com
Tianran Zhou
Huawei
Email: zhoutianran@huawei.com
Jie Dong
Huawei
Email: jie.dong@huawei.com
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Minxue Wang
China Mobile
Email: wangminxue@chinamobile.com
Nkosinathi Nzima
MTN
Email: Nkosinathi.Nzima@mtn.com
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