Interdomain Routing Working Group C. Li
Internet-Draft M. Chen
Intended status: Standards Track J. Dong
Expires: October 5, 2018 Z. Li
Huawei Technologies
April 3, 2018
Segment Routing Policies for Path Segment and Bi-directional Path
draft-li-idr-sr-policy-path-segment-distribution-00
Abstract
An SR policy is a set of candidate SR paths consisting of one or more
segment lists with necessary path attributes. For each SR path, it
may also have its own path attributes, and Path Segment is one of
them. A Path Segment is defined to identify an SR path, which can be
used for performance measurement, path correlation, and end-2-end
path protection. Path Segment can be also used to correlate two
unidirctional SR paths into a bi-directional SR path which is
required in some scenarios, for example, mobile backhaul transport
network.
This document defines extensions to BGP to distribute SR policies
carriying Path segment and bi-directional path information.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 5, 2018.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SR Policy for Path Identifier . . . . . . . . . . . . . . . . 3
3.1. SR Path ID Sub-TLV . . . . . . . . . . . . . . . . . . . 4
4. SR Policy for Bi-directional Path . . . . . . . . . . . . . . 5
4.1. SR Bi-directional Path Sub-TLV . . . . . . . . . . . . . 6
4.2. SR Reverse Path Segment List Sub-TLV . . . . . . . . . . 7
5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Segment routing (SR) [I-D.ietf-spring-segment-routing] is a source
routing paradigm that explicitly indicates the forwarding path for
packets at the ingress node. The ingress node steers packets into a
specific path according to the Segment Routing Policy ( SR Policy) as
defined in [I-D.filsfils-spring-segment-routing-policy]. For
distributing SR policies to the headend,
[I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by
using BGP, and new sub-TLVs are defined for SR Policies in BGP UPDATE
message.
In many use cases such as performance measurement, the path to which
the packets belong is required to be identified. Futhermore, in some
scenarios, for example, mobile backhaul transport network, there are
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requirements to support bi-directional path. However, there is no
path ID for each Segment List in the SR Policies defined in
[I-D.filsfils-spring-segment-routing-policy]. Also, the SR Policies
defined in [I-D.filsfils-spring-segment-routing-policy] only supports
uni-directional SR paths.
Therefore, this document defines the extension to SR policies that
carry path ID information in the Segment List and support bi-
directional path. The path ID can be a path segment in SR-MPLS
[I-D.cheng-spring-mpls-path-segment] , or a path ID in SRv6
[I-D.li-spring-passive-pm-for-srv6-np], or other IDs that can
identify a path. Also, this document defines extensions to BGP to
distribute SR policies carriying Path segment and bi-directional path
information.
2. Terminology
This memo makes use of the terms defined in
[I-D.ietf-spring-segment-routing] and
[I-D.ietf-idr-segment-routing-te-policy]. It also introduces the
following terminologies.
3. SR Policy for Path Identifier
As defined in [I-D.ietf-idr-segment-routing-te-policy] , the SR
Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes: Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Segment List
Weight
Segment
Segment
...
An SR path can be specified by an Segment List sub-TLV that contains
a set of segment sub-TLVs and other sub-TLVs as shown above.
As introduced in Section 1, each SR path may have a dedicated path
identifier, an SR policy carrying a SR path identifier is expressed
as below:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes: Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Segment List
Weight
Path ID
Segment
Segment
...
3.1. SR Path ID Sub-TLV
This section defines an SR Path ID sub-TLV to specify an SR path, and
it is included in the segment list sub-TLV.
An SR Path ID sub-TLV is associated with an SR path specified by a
segment list sub-TLV, and it MUST appear only once within a Segment
List sub-TLV. It has the following format:
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 | Flag | PIT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path ID (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. Path ID sub-TLV
Where:
Type: to be assigned by IANA (suggested value 10).
Length: the total length of the value field not including Type and
Length fields.
Flag: 8 bits of flags. Following flags are defined:
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| Reserved |G |E |
+--+--+--+--+--+--+--+--+
G-Flag: Global flag. Set when the Path segment/ID is global within
an SR domain.
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E-Flag: Egress flag for local sgement/ID. The E-flag should be set
when a path segment/ID is a local segment/ID allocated by the egress
node. Else, the path segment/ID is a local segment/ID allocated by
the ingress node. When the Path segment/ID is global within an SR
domain(G-flag is set), this flag should be ignored.
Reserved: 5 bits reserved and MUST be set to 0 on transmission and
MUST be ignored on receipt.
PIT: Path ID type, specifies the type of the Path ID, and it has
following types:
o 0: SR-MPLS Path Label
o 1: 4-octets integer Path ID
o 2: SRv6 SID
o 3-255:Reserved
Path ID: The Path ID of an SR path. The Path ID type is indicated by
the Path ID Type(PIT) field. It can be a path segment
[I-D.cheng-spring-mpls-path-segment], or it can be a 4 octets integer
ID as defined in [I-D.li-spring-passive-pm-for-srv6-np], or other IDs
that can identify a path.
When the type of Path ID is 0, and the E-flag and the G-flag are
unset, meaning the Path ID is a local path label allocated by the
ingress node in SR-MPLS, a path can be identified by a combination of
this path ID and a non-routable Source label, as defined at section
2.2 in [I-D.cheng-spring-mpls-path-segment]. The non-routable Source
Label, as known as a non-routable source node ID, can be configured
by many ways like CLI, and it is out of scope of this document and
will be discussed in other documents.
4. SR Policy for Bi-directional Path
In some scenarios, for example, mobile backhaul transport network,
there are requirements to support bi-directional path. In SR, a bi-
directional path can be represented as a binding of two uni-
directional SR paths. This document also defines new sub-TLVs to
describe an SR bi-directional path. An SR policy carrying SR bi-
directional path information is expressed as below:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes: Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Bi-directioanl Path
Segment List
Weight
Path ID
Segment
Segment
...
Reverse Segment List
Weight
Path ID
Segment
Segment
...
4.1. SR Bi-directional Path Sub-TLV
This section defines an SR bi-directional path sub-TLV to specify a
bi-directional path, which contains a Segment List sub-TLV
[I-D.ietf-idr-segment-routing-te-policy] and an associated Reverse
Path Segment List as defined at section 4.2. The SR bi-directional
path sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. SR Bi-directional path sub-TLV
Where:
Type: TBA, and the suggest value is 14.
Length: the total length of the sub-TLVs encoded within the SR Bi-
directional Path Sub-TLV not including Type and Length fields.
RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission
and MUST be ignored on receipt.
Sub-TLVs:
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o An Segment List sub-TLV
o An associated Reverse Path Segment List sub-TLV
4.2. SR Reverse Path Segment List Sub-TLV
An SR Reverse Path Segment List sub-TLV is defined to specify an SR
reverse path associated with the path specified by the Segment List
in the same SR Bi-directional Path Sub-TLV, and it has the following
format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. SR Reverse Path Segment List Sub-TLV
where:
Type: TBA, and suggest value is 127.
Length: the total length of the sub-TLVs encoded within the SR
Reverse Path Segment List Sub-TLV not including the Type and Length
fields.
RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission
and MUST be ignored on receipt.
sub-TLVs:
o An optional single Weight sub-TLV.
o An mandatory SR Path ID sub-TLV that contains the path ID of the
reverse SR path.
o Zero or more Segment sub-TLVs to specify the reverse SR path.
The Segment sub-TLVs in the Reverse Path Segment List sub-TLV
provides the information of the reverse SR path, which can be used
for directing egress BFD peer to use specific path for the reverse
direction of the BFD session [I-D.ietf-mpls-bfd-directed] or other
applications.
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5. Operations
The document does not bring new operation beyong the description of
operations defined in [I-D.ietf-idr-segment-routing-te-policy]. The
existing operations defined in
[I-D.ietf-idr-segment-routing-te-policy] can apply to this document
directly.
Typically but not limit to, the uni-directional or bi-directional SR
policies carrying path identification infomation are configured by a
controller.
After configuration, the uni-directional or bi-directional SR
policies carrying path identification infomation will be advertised
by BGP update messages. The operation of advertisement is the same
as defined in [I-D.ietf-idr-segment-routing-te-policy], as well as
the receiption.
The consumer of the uni-directional or bi-directional SR policies is
not the BGP process, it can be any applications, such as performance
measurement. The operation of sending information to consumers is
out of scope of this document.
6. IANA Considerations
TBA
7. Security Considerations
TBA
8. Acknowledgements
TBA
9. References
9.1. Normative References
[I-D.cheng-spring-mpls-path-segment]
Cheng, W., Wang, L., Li, H., Chen, M., Zigler, R., and S.
Zhan, "Path Segment in MPLS Based Sement Routing Network",
draft-cheng-spring-mpls-path-segment-01 (work in
progress), March 2018.
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[I-D.filsfils-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Raza, K., Liste, J., Clad,
F., Talaulikar, K., Ali, Z., Hegde, S.,
daniel.voyer@bell.ca, d., Lin, S., bogdanov@google.com,
b., Krol, P., Horneffer, M., Steinberg, D., Decraene, B.,
Litkowski, S., and P. Mattes, "Segment Routing Policy for
Traffic Engineering", draft-filsfils-spring-segment-
routing-policy-05 (work in progress), February 2018.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen,
E., and S. Lin, "Advertising Segment Routing Policies in
BGP", draft-ietf-idr-segment-routing-te-policy-02 (work in
progress), March 2018.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[I-D.li-spring-passive-pm-for-srv6-np]
Li, C. and M. Chen, "Passive Performance Measurement for
SRv6 Network Programming", draft-li-spring-passive-pm-for-
srv6-np-00 (work in progress), March 2018.
[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>.
9.2. Informative References
[I-D.ietf-mpls-bfd-directed]
Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
"Bidirectional Forwarding Detection (BFD) Directed Return
Path", draft-ietf-mpls-bfd-directed-08 (work in progress),
December 2017.
Authors' Addresses
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: chengli13@huawei.com
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Mach(Guoyi) Chen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: Mach.chen@huawei.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
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