Segment Routing Prefix SID extensions for BGP
draft-keyupate-idr-bgp-prefix-sid-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Keyur Patel , Saikat Ray , Stefano Previdi , Clarence Filsfils | ||
| Last updated | 2014-10-25 | ||
| Replaced by | draft-ietf-idr-bgp-prefix-sid, RFC 8669 | ||
| RFC stream | (None) | ||
| Formats | |||
| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-keyupate-idr-bgp-prefix-sid-00
IDR K. Patel
Internet-Draft S. Ray
Intended status: Standards Track S. Previdi
Expires: April 28, 2015 C. Filsfils
Cisco Systems
October 25, 2014
Segment Routing Prefix SID extensions for BGP
draft-keyupate-idr-bgp-prefix-sid-00
Abstract
Segment Routing (SR) architecture allows a node to steer a packet
flow through any topological path and service chain by leveraging
source routing. The ingress node prepends a SR header to a packet
containing a set of "segments". Each segment represents a
topological or a service-based instruction. Per-flow state is
maintained only at the ingress node of the SR domain.
The Segment Routing architecture can be implemented using MPLS with
no changes to the forwarding plane. It requires minor extensions to
the existing routing protocols.
This document describes the BGP extension for announcing BGP Prefix
Segment Identifier (BGP Prefix SID) 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."
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This Internet-Draft will expire on April 28, 2015.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Segment Routing Documents . . . . . . . . . . . . . . . . . . 3
4. BGP-Prefix-SID . . . . . . . . . . . . . . . . . . . . . . . 3
5. BGP-Prefix-SID Label Index Attribute . . . . . . . . . . . . 4
6. Receiving BGP-Prefix-SID Label Index Attribute . . . . . . . 5
7. Announcing BGP-Prefix-SID Label Index Attribute . . . . . . . 5
8. Error Handling of BGP-Prefix-SID Label Index Attribute . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 7
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
13.1. Normative References . . . . . . . . . . . . . . . . . . 7
13.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Segment Routing (SR) architecture leverages the source routing
paradigm. A group of inter-connected nodes that use SR forms a SR
domain. The ingress node of the SR domain prepends a SR header
containing "segments" to an incoming packet. Each segment represents
a topological instruction (such as "go to prefix P following shortest
path") or a service instruction ("pass through deep packet
inspection"). By inserting the desired sequence of instructions, the
ingress node is able to steer a packet via any topological path and/
or service chain; per-flow state is maintained only at the ingress
node of the SR domain.
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Each segment is identified by a Segment Identifier (SID). By using
MPLS labels as SIDs, the SR architecture can be implemented using the
existing MPLS dataplane.
A BGP-Prefix Segment (aka BGP-Prefix-SID), is a BGP segment attached
to a BGP prefix. A BGP-Prefix-SID is always global within the SR/BGP
domain and identifies an instruction to forward the packet over the
ECMP-aware best-path computed by BGP to the related prefix. The BGP-
Prefix-SID is the identifier of the BGP prefix segment.
This document describes the BGP extension to signal the BGP-Prefix-
SID. Specifically, this document defines a new BGP attribute known
as BGP Label index attribute (carrying the BGP Prefix SID) and
specifies the rules to originate, receive and handle error conditions
of the new attribute.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
be interpreted as described in [RFC2119] only when they appear in all
upper case. They may also appear in lower or mixed case as English
words, without any normative meaning.
3. Segment Routing Documents
The main reference for this document is the SR architecture defined
in [I-D.filsfils-spring-segment-routing].
The Segment Routing Egress Peer Engineering architecture is described
in [I-D.filsfils-spring-segment-routing-central-epe].
The Segment Routing Egress Peer Engineering BGPLS extensions are
described in [I-D.previdi-idr-bgpls-segment-routing-epe].
A practical use case of the BGP Prefix SID is illustrated in
[I-D.filsfils-spring-segment-routing-msdc].
4. BGP-Prefix-SID
The BGP-Prefix-SID attached to a BGP prefix P represents the
instruction "go to Prefix P" along its BGP bestpath (potentially
ECMP-enabled). This Segment is realized on a MPLS dataplane in the
following way:
According to [I-D.filsfils-spring-segment-routing], each BGP
speaker is configured with a label block called Segment Routing
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Global Block (SRGB). The SRGB could be different on different
speakers.
The operator assigns a globally unique "index", L_I, to a locally
sourced prefix of a BGP speaker N which is advertised to all other
BGP speakers in the SR domain.
The index L_I is a 32 bit offset in the SRGB. Each BGP speaker
derives its local MPLS label, L, by adding L_I to the start value
of its own SRGB, and programs L in its MPLS dataplane as its
incoming/local label for the prefix.
If the BGP speakers are configured with the same SRGB start value,
they will all program the same MPLS label value for a given prefix
P. This has the effect of having a single label value for prefix
P across all BGP speakers despite the MPLS paradigm of "local
label" is preserved.
In order to advertise the SRGB label index of a given prefix P, a new
extension to BGP is needed. This extension is described in
subsequent sections.
5. BGP-Prefix-SID Label Index Attribute
BGP Prefix Label Index is a new optional, transitive BGP path
attribute. The attribute type code for BGP Label Index attribute is
to be assigned by IANA. The value field of the Label Index attribute
has 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o RESERVED: 16 bit field. SHOULD be unset on transmission and MUST
be ignored on reception.
o Flags: 16 bits of flags. None are defined in this document.
Flags SHOULD be unset on transmission an MUST be ignored at
reception.
o Label Index: 32 bit value representing the index value in the SRGB
space.
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Using the BGP protocol Label index as an offset, a label value for a
given prefix is computed from a BGP SRGB. The BGP SRGB protocol
label block is configured explicitly on each BGP Speaker enabled with
BGP-Prefix-SID extensions.
6. Receiving BGP-Prefix-SID Label Index Attribute
It is assumed that a BGP speaker is configured with an SRGB=[GB_S,
GB_E]. Given a label index L_I, we call L = L_I + GB_S as the
derived label. A BGP Label Index attribute is called "unacceptable"
for a speaker M if the derived label value L lies outside the SRGB
configured on M. Otherwise the Label Index attribute is called
"acceptable" to speaker M.
When a BGP speaker receives a path from a neighbor with an acceptable
BGP Label Index attribute, it SHOULD program the derived label as the
local label for the prefix in its MPLS dataplane. In case of any
error, a BGP speaker MUST resort to the error handling rules
specified in the later section of the document. A BGP speaker MAY
log an error for further analysis.
When a BGP speaker receives a path from a neighbor with an
unacceptable BGP Label Index attribute, for the purpose of label
allocation, it SHOULD treat the path as if it came without a Label
Index attribute. A BGP speaker MAY choose to assign a local (also
called dynamic) label (non-SRGB) for such a prefix. A BGP speaker
MAY log an error for further analysis.
A BGP speaker receiving a BGP Label index attribute from its EBGP
neighbor SHOULD discard the attribute unless it is configured to
accept the attribute from the EBGP neighbor. A BGP speaker MAY log
an error when discarding an attribute for further analysis.
A BGP speaker receiving a prefix with a Label index attribute and a
label NLRI field of implicit-null from a neighbor MUST adhere to
standard behavior and program its MPLS dataplane to pop the top label
when forwarding traffic to the prefix.The label NLRI defines the
outbound label that MUST be used by the receiving node. The Label
Index gives a hint to the receiving node on which local/incoming
label he SHOULD use.
7. Announcing BGP-Prefix-SID Label Index Attribute
A BGP speaker that originates a prefix attaches the Label Index
attribute when it advertises the prefix to its neighbors. The value
of the Label Index is determined by configuration.
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A BGP speaker that advertises a path received from one of its
neighbors SHOULD advertise the Label Index received with the path
without modification regardless of whether the Label Index was
acceptable. If the path did not come with a Label Index attribute,
the speaker MAY attach a Label Index to the path if configured to do
so. The value of the Label Index is determined by the configuration.
In all cases, the label field of the NLRI ([RFC3107], [RFC4364]) MUST
be set to the label programmed in the MPLS dataplane for the given
prefix. If the prefix is that of a local interface of the speaker,
this label is the usual MPLS label (such as implicit or explicit NULL
label).
The BGP Label Index attribute SHOULD only be announced with BGP
Prefixes carried in a labeled address-family (SAFI value 4 or SAFI
value 128). Since the BGP Label index value must be unique within an
SR domain, by default an implementation SHOULD NOT advertise the BGP
Label Index attribute outside an Autonomous System unless it is
explicitly configured to do so. To contain distribution of the BGP
Label Index attribute beyond its intended scope of applicability,
attribute filtering MAY be deployed.
8. Error Handling of BGP-Prefix-SID Label Index Attribute
When a BGP Speaker receives a BGP Update message containing more than
one, or a malformed BGP Label Index attribute, it MUST ignore the
received BGP Label Index attributes and not pass it to other BGP
peers. (see [I-D.ietf-idr-error-handling], Section 7). This is
equivalent to the -attribute discard- action specified in
[[I-D.ietf-idr-error-handling]. A BGP speaker MAY log an error when
discarding an attribute for further analysis.
When a BGP Speaker receives a BGP Label Index attribute that is
attached to prefixes belonging to SAFI value other than 4 or 128, it
MUST quietly ignore the received attribute and not pass it to other
BGP peers. A BGP speaker MAY log an error for further analysis.
When a BGP speaker receives an unacceptable Label Index attribute, it
MAY log an error for further analysis.
9. IANA Considerations
This document defines a new BGP attribute known as BGP Label Index
attribute. This document requests IANA to assign a new attribute
code type for BGP Label Index attribute from the BGP Path Attributes
registry.
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10. Security Considerations
This document introduces no new security considerations above and
beyond those already specified in [RFC4271] and [RFC3107].
11. Acknowledgements
TBD
12. Change Log
Initial Version: Sep 21 2014
13. References
13.1. Normative References
[I-D.ietf-idr-error-handling]
Chen, E., Scudder, J., Mohapatra, P., and K. Patel,
"Revised Error Handling for BGP UPDATE Messages", draft-
ietf-idr-error-handling-14 (work in progress), September
2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, May 2001.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
13.2. Informative References
[I-D.filsfils-spring-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-spring-
segment-routing-04 (work in progress), July 2014.
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[I-D.filsfils-spring-segment-routing-central-epe]
Filsfils, C., Previdi, S., Patel, K., Aries, E.,
shaw@fb.com, s., Ginsburg, D., and D. Afanasiev, "Segment
Routing Centralized Egress Peer Engineering", draft-
filsfils-spring-segment-routing-central-epe-02 (work in
progress), July 2014.
[I-D.filsfils-spring-segment-routing-msdc]
Filsfils, C., "BGP-Prefix Segment in large-scale data
centers", 2014.
[I-D.previdi-idr-bgpls-segment-routing-epe]
Previdi, S., Filsfils, C., Ray, S., and K. Patel, "Segment
Routing Egress Peer Engineering BGPLS Extensions", draft-
previdi-idr-bgpls-segment-routing-epe-00 (work in
progress), May 2014.
Authors' Addresses
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95124 95134
USA
Email: keyupate@cisco.com
Saikat Ray
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95124 95134
USA
Email: sairay@cisco.com
Stefano Previdi
Cisco Systems
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
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Clarence Filsfils
Cisco Systems
Brussels
Belgium
Email: cfilsfils@cisco.com
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