Advertising Segment Routing Traffic Engineering Policies in BGP
draft-previdi-idr-segment-routing-te-policy-02
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 | Stefano Previdi , Clarence Filsfils , Arjun Sreekantiah , Siva Sivabalan , Paul Mattes , Eric C. Rosen , Steven Lin | ||
| Last updated | 2016-10-30 (Latest revision 2016-05-27) | ||
| Replaces | draft-sreekantiah-idr-segment-routing-te | ||
| Replaced by | draft-ietf-idr-segment-routing-te-policy, draft-ietf-idr-segment-routing-te-policy | ||
| 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 | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-previdi-idr-segment-routing-te-policy-02
Network Working Group S. Previdi, Ed.
Internet-Draft C. Filsfils
Intended status: Standards Track A. Sreekantiah
Expires: May 3, 2017 S. Sivabalan
Cisco Systems, Inc.
P. Mattes
Microsoft
E. Rosen
Juniper Networks
S. Lin
Google
October 30, 2016
Advertising Segment Routing Traffic Engineering Policies in BGP
draft-previdi-idr-segment-routing-te-policy-02
Abstract
This document defines a new BGP SAFI with a new NLRI in order to
advertise a Segment Routing Traffic Engineering Policy (SR TE
Policy). An SR TE Policy is a set of explicit paths represented by
one or more segment lists. The SR TE Policy is advertised along with
the Tunnel Encapsulation Attribute for which this document also
defines new sub-TLVs. An SR TE policy is advertised with the
information that will be used by the node receiving the advertisement
in order to instantiate the policy in its forwarding table and to
steer traffic according to the policy.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 3, 2017.
Previdi, et al. Expires May 3, 2017 [Page 1]
Internet-Draft Segment Routing TE Policies in BGP October 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. SR TE Policy Encoding . . . . . . . . . . . . . . . . . . . . 4
2.1. SR TE Policy SAFI and NLRI . . . . . . . . . . . . . . . 4
2.2. SR TE Policy and Tunnel Encapsulation Attribute . . . . . 6
2.3. Remote Endpoint and Color . . . . . . . . . . . . . . . . 7
2.4. SR TE Policy Sub-TLVs . . . . . . . . . . . . . . . . . . 7
2.4.1. Preference sub-TLV . . . . . . . . . . . . . . . . . 7
2.4.2. SR TE Binding SID Sub-TLV . . . . . . . . . . . . . . 8
2.4.3. Weight Sub-TLV . . . . . . . . . . . . . . . . . . . 9
2.4.4. Segment List Sub-TLV . . . . . . . . . . . . . . . . 10
2.4.5. Segment Sub-TLV . . . . . . . . . . . . . . . . . . . 11
3. SR TE Policy Operations . . . . . . . . . . . . . . . . . . . 20
3.1. Configuration and Advertisement of SR TE Policies . . . . 20
3.2. Multipath Operation . . . . . . . . . . . . . . . . . . . 21
3.3. Binding SID TLV . . . . . . . . . . . . . . . . . . . . . 21
3.4. Reception of an SR TE Policy . . . . . . . . . . . . . . 21
3.4.1. Acceptance of a SR TE Policy Update . . . . . . . . . 22
3.4.2. Usable SR TE Policy . . . . . . . . . . . . . . . . . 23
3.4.3. Instantiation of an SR TE Policy . . . . . . . . . . 24
3.4.4. Propagation of an SR TE Policy . . . . . . . . . . . 25
3.5. Steering Traffic into a SR TE Policy . . . . . . . . . . 25
3.6. Flowspec and SR TE Policies . . . . . . . . . . . . . . . 26
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1. Normative References . . . . . . . . . . . . . . . . . . 27
7.2. Informational References . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
Previdi, et al. Expires May 3, 2017 [Page 2]
Internet-Draft Segment Routing TE Policies in BGP October 2016
1. Introduction
Segment Routing (SR) technology leverages the source routing and
tunneling paradigms. [I-D.ietf-spring-segment-routing] describes the
SR architecture. [I-D.ietf-spring-segment-routing-mpls] describes
its instantiation on the MPLS data plane and
[I-D.ietf-6man-segment-routing-header] describes the Segment Routing
instantiation over the IPv6 data plane.
This document defines the Segment Routing Traffic Engineering Policy
(SR TE Policy) as a set of unequal equal cost multi-path (UCMP)
segment lists (representing explicit paths) as well as the mechanism
allowing a router to steer traffic into an SR TE Policy.
The SR TE Policy is advertised in the Border Gateway Protocol (BGP)
by the BGP speaker being a router or a controller and using
extensions defined in this document. Among the information encoded
in the BGP message and representing the SR TE Policy, the steering
mechanism makes also use of the Extended Color Community currently
defined in [I-D.ietf-idr-tunnel-encaps]
Typically, a controller defines the set of policies and advertise
them to BGP routers (typically ingress routers). The policy
advertisement uses BGP extensions defined in this document. The
policy advertisement is, in most but not all of the cases, tailored
for the receiver. In other words, a policy advertised to a given BGP
speaker has significance only for that particular router and is not
intended to be propagated anywhere else. Then, the receiver of the
policy instantiate the policy in its routing and forwarding tables
and steer traffic into it based on both the policy and destination
prefix color and next-hop.
Alternatively, a router (i.e.: an BGP egress router) advertises SR TE
Policies representing paths to itself. These advertisements are sent
to BGP ingress nodes who instantiate these policies and steer traffic
into them according to the color and endpoint/BGP next-hop of both
the policy and the destination prefix.
An SR TE Policy being intended only for the receiver of the
advertisement, the SR TE Policies are sent directly to each receiver
and, in most of the cases will not traverse any Route Reflector (RR,
[RFC4456]).
However, there are cases where a SR TE Policy is intended to a group
of nodes. Also, in a deployment scenario, a controller may also rely
on the standard BGP update propagation scheme which makes use of
route reflectors. This cases require mechanisms that:
Previdi, et al. Expires May 3, 2017 [Page 3]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o Uniquely identify each instance of a given policy.
o Uniquely identify the intended receiver of a given SR TE Policy
advertisement.
The BGP extensions for the advertisement of SR TE Policies include
following components:
o A new Subsequent Address Family Identifier (SAFI) identifying the
content of the BGP message (i.e.: the SR TE Policy).
o A new NLRI identifying the SR TE Policy.
o A set of new TLVs to be inserted into the Tunnel Encapsulation
Attribute (as defined in [I-D.ietf-idr-tunnel-encaps]) and
describing the SR TE Policy.
o An IPv4 address format route-target extended community ([RFC4360])
attached to the SR TE Policy advertisement and that indicates the
intended receiver of such SR TE Policy advertisement.
o The Extended Color Community (as defined in
[I-D.ietf-idr-tunnel-encaps]) and used in order to steer traffic
into an SR TE Policy.
1.1. 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].
2. SR TE Policy Encoding
2.1. SR TE Policy SAFI and NLRI
A new SAFI is defined: the SR TE Policy SAFI (codepoint suggested
value 73, to be assigned by IANA).
The SR TE Policy SAFI uses a new NLRI defined as follows:
Previdi, et al. Expires May 3, 2017 [Page 4]
Internet-Draft Segment Routing TE Policies in BGP October 2016
+-----------------------------------------------+
| Distinguisher (4 octets) |
+-----------------------------------------------+
| Policy Color (4 octets) |
+-----------------------------------------------+
| Endpoint (4 or 16 octets) |
+-----------------------------------------------+
where:
o Distinguisher: 4-octet value uniquely identifying the policy in
the context of <color, endpoint> tuple. The distinguisher has no
semantic and it's solely used by the SR TE Policy originator in
order to make unique (from a NLRI perspective) multiple
occurrences of the same SR TE Policy.
o Policy Color: 4-octet value identifying (with the endpoint) the
policy. The color is used to match the color of the destination
prefixes in order to steer traffic into the SR TE Policy.
o Endpoint: identifies the endpoint of a policy. The Endpoint may
represent a single node or a set of nodes (e.g.: an anycast
address or a summary address). The Endpoint is an IPv4 (4-octet)
address or an IPv6 (16-octet) address according to the AFI of the
NLRI.
The NLRI containing the SR TE Policy is carried in a BGP UPDATE
message [RFC4271] using BGP multiprotocol extensions [RFC4760] with
an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of 73 (suggested
value, to be assigned by IANA).
An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI
attribute with the SR TE Policy SAFI MUST also carry the BGP
mandatory attributes. In addition, the BGP update message MAY also
contain any of the BGP optional attributes.
The next-hop of the SR TE Policy SAFI NLRI is set based on the AFI.
For example, if the AFI is set to IPv4 (1), then the next-hop is
encoded as a 4-byte IPv4 address. If the AFI is set to IPv6 (2),
then the next-hop is encoded as a 16-byte IPv6 address of the router.
It is important to note that any BGP speaker receiving a BGP message
with an SR TE Policy NLRI, will process it only if the NLRI is a best
path as per the BGP best path selection algorithm.
Previdi, et al. Expires May 3, 2017 [Page 5]
Internet-Draft Segment Routing TE Policies in BGP October 2016
2.2. SR TE Policy and Tunnel Encapsulation Attribute
The content of the SR TE Policy is encoded in the Tunnel
Encapsulation Attribute originally defined in
[I-D.ietf-idr-tunnel-encaps] using a new Tunnel-Type TLV (suggested
codepoint is 14, to be assigned by IANA).
The SR TE Policy Encoding structure is as follows:
SR TE Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR TE Policy
Binding SID
Preference
Segment List
Weight
Segment
Segment
...
...
...
where:
o SR TE Policy SAFI NLRI is defined in Section 2.1.
o Tunnel Encapsulation Attribute is defined in
[I-D.ietf-idr-tunnel-encaps].
o Tunnel-Type is set to a suggested value of 14 (to be assigned by
IANA).
o Preference, Binding SID, Weight, Segment and Segment-List are new
sub-TLVs defined in this document.
o Additional sub-TLVs may be defined in the future.
A single occurrence of "Tunnel Type: SR TE Policy" MUST be encoded
within the same Tunnel Encapsulation Attribute.
Multiple occurrences of "Segment List" MAY be encoded within the same
SR TE Policy.
Multiple occurrences of "Segment" MAY be encoded within the same
Segment List.
Previdi, et al. Expires May 3, 2017 [Page 6]
Internet-Draft Segment Routing TE Policies in BGP October 2016
2.3. Remote Endpoint and Color
The Remote Endpoint and Color sub-TLVs, as defined in
[I-D.ietf-idr-tunnel-encaps], MAY also be present in the SR TE Policy
encodings.
If present, the Remote Endpoint sub-TLV MUST match the Endpoint of
the SR TE Policy SAFI NLRI.
If present, the Color sub-TLV MUST match the Policy Color of the SR
TE Policy SAFI NLRI.
2.4. SR TE Policy Sub-TLVs
This section defines the SR TE Policy sub-TLVs.
2.4.1. Preference sub-TLV
The Preference sub-TLV is used in order to determine the preference
among multiple SR TE Policy originators.
The Preference sub-TLV is optional, MAY appear only once in the SR TE
Policy and 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value is 6).
o Length: 6.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o Preference: a 4-octet value. The highest value is preferred.
The Preference is used when the same <color,endpoint> policy is
advertised by multiple originators of the same SR TE Policy. The
Previdi, et al. Expires May 3, 2017 [Page 7]
Internet-Draft Segment Routing TE Policies in BGP October 2016
Preference is used by the receiver in order to determine which of the
received policies are to be installed. The following rules apply to
the Preference:
o Preference is to be applied to the <color,endpoint> tuple. The
Distinguisher MUST NOT be considered.
o Preference is used in order to determine which instance of a given
SR TE Policy is to be installed. However, Preference MUST NOT
influence the BGP selection algorithm and propagation rules. In
other words, the preference selection happens after the BGP path
selection.
2.4.2. SR TE Binding SID Sub-TLV
The Binding SID sub-TLV requests the allocation of a Binding Segment
identifier associated with the SR TE Policy.
The Binding SID sub-TLV is optional, MAY appear only once in the SR
TE Policy and 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding SID (variable, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value is 7).
o Length: specifies the length of the value field not including Type
and Length fields. Can be 2 or 6 or 18.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o Binding SID: if length is 2, then no Binding SID is present. If
length is 6 then the Binding SID contains a 4-octet SID. If
length is 18 then the Binding SID contains a 16-octet IPv6 SID.
The Binding SID sub-TLV is used to instruct the receiver of the BGP
message to allocate a Binding SID to the SR TE Policy. The
Previdi, et al. Expires May 3, 2017 [Page 8]
Internet-Draft Segment Routing TE Policies in BGP October 2016
allocation of the Binding SID in the receiver is done according to
following rules:
o If length is 2 (no value field is present), then the receiver MUST
allocate a local Binding SID whose value is chosen by the
receiver.
o If length is 6, then the value field contains the 4-octet Binding
SID value the receiver SHOULD allocate.
o If length is 18, then the value field contains the 16-octet
Binding SID value the receiver SHOULD allocate.
When a controller is used in order to define and advertise SR TE
Policies and when the Binding SID is allocated by the receiver, such
Binding SID SHOULD be reported to the controller. The mechanisms
and/or APIs used for the reporting of the Binding SID are outside the
scope of this document.
Further use of the Binding SID is described in a subsequent section.
2.4.3. Weight Sub-TLV
The Weight sub-TLV specifies the weight associated to a given path
(i.e.: a given segment list). The weight is used in order to apply
weighted UCMP mechanism when steering traffic into a policy that
includes multiple Segment Lists sub-TLVs (i.e.: multiple explicit
paths).
The Weight sub-TLV is optional, MAY only appear once in the Segment
List sub-TLV, and 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: to be assigned by IANA (suggested value is 9).
Length: 6.
Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
Previdi, et al. Expires May 3, 2017 [Page 9]
Internet-Draft Segment Routing TE Policies in BGP October 2016
RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission
and MUST be ignored on receipt.
When present, the Weight sub-TLV specifies a weight to be associated
with the corresponding Segment List, for use in unequal cost multi-
path. Weights are applied by summing the total value of all of the
weights for all Segment Lists, and then assigning a fraction of the
forwarded traffic to each Segment List in proportion its weight's
fraction of the total.
2.4.4. Segment List Sub-TLV
The Segment List sub-TLV is used in order to encode a single explicit
path towards the endpoint. The Segment List sub-TLV includes the
elements of the paths (i.e.: segments) as well as an optional Weight
TLV.
The Segment List sub-TLV may exceed 255 bytes length due to large
number of segments. Therefore a 2-octet length is required.
According to [I-D.ietf-idr-tunnel-encaps], the first bit of the sub-
TLV code point defines the size of the length field. Therefore, for
the Segment List sub-TLV a code point of 128 (suggested value, to be
assigned by IANA) is used.
The Segment List sub-TLV is mandatory, MAY appear multiple times in
the SR TE Policy and 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 //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value is 128).
o Length: the total length (not including the Type and Length
fields) of the sub-TLVs encoded within the Segment List sub-TLV.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o sub-TLVs:
* An optional single Weight sub-TLV.
Previdi, et al. Expires May 3, 2017 [Page 10]
Internet-Draft Segment Routing TE Policies in BGP October 2016
* One or more Segment sub-TLVs.
The Segment List sub-TLV is mandatory.
Multiple occurrences of the Segment List sub-TLV MAY appear in the SR
TE Policy.
When multiple occurrences of the Segment List sub-TLV appear in the
SR TE Policy, the traffic is load-balanced across them either through
an ECMP scheme (if no Weight sub-TLV is present) or through a
weighted UCMP scheme according to Section 2.4.3.
2.4.5. Segment Sub-TLV
The Segment sub-TLV describes a single segment in a segment list
(i.e.: a single element of the explicit path). Multiple Segment sub-
TLVs constitute an explicit path of the SR TE Policy.
The Segment sub-TLV is mandatory and MAY appear multiple times in the
Segment List sub-TLV.
This document defines 8 different types of Segment Sub-TLVs:
Type 1: SID only, in the form of MPLS Label
Type 2: SID only, in the form of IPv6 address
Type 3: IPv4 Node Address with optional SID
Type 4: IPv6 Node Address with optional SID
Type 5: IPv4 Address + index with optional SID
Type 6: IPv4 Local and Remote addresses with optional SID
Type 7: IPv6 Address + index with optional SID
Type 8: IPv6 Local and Remote addresses with optional SID
2.4.5.1. Type 1: SID only, in the form of MPLS Label
The Type-1 Segment Sub-TLV encodes a single SID in the form of an
MPLS label. The format is 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 1, to be assigned by IANA.
Previdi, et al. Expires May 3, 2017 [Page 11]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o Length is 6.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o Label: 20 bits of label value.
o TC: 3 bits of traffic class.
o S: 1 bit of bottom-of-stack.
o TTL: 1 octet of TTL.
The following applies to the Type-1 Segment sub-TLV:
o The S bit SHOULD be zero upon transmission, and MUST be ignored
upon reception.
o If the originator wants the receiver to choose the TC value, it
sets the TC field to zero.
o If the originator wants the receiver to choose the TTL value, it
sets the TTL field to 255.
o If the originator wants to recommend a value for these fields, it
puts those values in the TC and/or TTL fields.
o The receiver MAY override the originator's values for these
fields. This would be determined by local policy at the receiver.
One possible policy would be to override the fields only if the
fields have the default values specified above.
2.4.5.2. Type 2: SID only, in the form of IPv6 address
The Type-2 Segment Sub-TLV encodes a single SID in the form of an
IPv6 address. The format is as follows:
Previdi, et al. Expires May 3, 2017 [Page 12]
Internet-Draft Segment Routing TE Policies in BGP October 2016
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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 2, to be assigned by IANA.
o Length is 18.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o IPv6 SID: 16 octets of IPv6 address.
The IPv6 Segment Identifier (IPv6 SID) is defined in
[I-D.ietf-6man-segment-routing-header].
2.4.5.3. Type 3: IPv4 Node Address with optional SID
The Type-3 Segment Sub-TLV encodes an IPv4 node address and an
optional SID in the form of either an MPLS label or an IPv6 address.
The format is 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SID (optional, 4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 3, to be assigned by IANA.
o Length is 6 or 10 or 22.
Previdi, et al. Expires May 3, 2017 [Page 13]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o IPv4 Node Address: a 4 octet IPv4 address representing a node.
o SID: either 4 octet MPLS SID or a 16 octet IPv6 address.
The following applies to the Type-3 Segment sub-TLV:
o The IPv4 Node Address MUST be present.
o The SID is optional and MAY be of one of the following formats:
* MPLS SID: a 4 octet label containing label, TC, S and TTL as
defined in Section 2.4.5.1.
* IPV6 SID: a 16 octet IPv6 address.
o If length is 6, then only the IPv4 Node Address is present.
o If length is 10, then the IPv4 Node Address and the MPLS SID are
present.
o If length is 22, then the IPv4 Node Address and the IPv6 SID are
present.
2.4.5.4. Type 4: IPv6 Node Address with optional SID
The Type-4 Segment Sub-TLV encodes an IPv6 node address and an
optional SID in the form of either an MPLS label or an IPv6 address.
The format is 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SID (optional, 4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 4, to be assigned by IANA.
Previdi, et al. Expires May 3, 2017 [Page 14]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o Length is 18 or 22 or 34.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o IPv6 Node Address: a 16 octet IPv6 address representing a node.
o SID: either 4 octet MPLS SID or a 16 octet IPv6 address.
The following applies to the Type-4 Segment sub-TLV:
o The IPv6 Node Address MUST be present.
o The SID is optional and MAY be of one of the following formats:
* MPLS SID: a 4 octet label containing label, TC, S and TTL as
defined in Section 2.4.5.1.
* IPV6 SID: a 16 octet IPv6 address.
o If length is 18, then only the IPv6 Node Address is present.
o If length is 22, then the IPv6 Node Address and the MPLS SID are
present.
o If length is 34, then the IPv6 Node Address and the IPv6 SID are
present.
2.4.5.5. Type 5: IPv4 Address + index with optional SID
The Type-5 Segment Sub-TLV encodes an IPv4 node address, an interface
index (IfIndex) and an optional SID in the form of either an MPLS
label or an IPv6 address. The format is as follows:
Previdi, et al. Expires May 3, 2017 [Page 15]
Internet-Draft Segment Routing TE Policies in BGP October 2016
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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IfIndex (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SID (optional, 4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 5, to be assigned by IANA.
o Length is 10 or 14 or 26.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o IfIndex: 4 octets of interface index.
o IPv4 Node Address: a 4 octet IPv4 address representing a node.
o SID: either 4 octet MPLS SID or a 16 octet IPv6 address.
The following applies to the Type-5 Segment sub-TLV:
o The IPv4 Node Address MUST be present.
o The Interface Index (IfIndex) MUST be present.
o The SID is optional and MAY be of one of the following formats:
* MPLS SID: a 4 octet label containing label, TC, S and TTL as
defined in Section 2.4.5.1.
* IPV6 SID: a 16 octet IPv6 address.
o If length is 10, then the IPv4 Node Address and IfIndex are
present.
o If length is 14, then the IPv4 Node Address, the IfIndex and the
MPLS SID are present.
Previdi, et al. Expires May 3, 2017 [Page 16]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o If length is 26, then the IPv4 Node Address, the IfIndex and the
IPv6 SID are present.
2.4.5.6. Type 6: IPv4 Local and Remote addresses with optional SID
The Type-6 Segment Sub-TLV encodes an IPv4 node address, an adjacency
local address, an adjacency remote address and an optional SID in the
form of either an MPLS label or an IPv6 address. The format is 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SID (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 6, to be assigned by IANA.
o Length is 10 or 14 or 26.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o Local IPv4 Address: a 4 octet IPv4 address.
o Remote IPv4 Address: a 4 octet IPv4 address.
o SID: either 4 octet MPLS SID or a 16 octet IPv6 address.
The following applies to the Type-6 Segment sub-TLV:
o The Local IPv4 Address MUST be present and represents an adjacency
local address.
o The Remote IPv4 Address MUST be present and represents the remote
end of the adjacency.
Previdi, et al. Expires May 3, 2017 [Page 17]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o The SID is optional and MAY be of one of the following formats:
* MPLS SID: a 4 octet label containing label, TC, S and TTL as
defined in Section 2.4.5.1.
* IPV6 SID: a 16 octet IPv6 address.
o If length is 10, then only the IPv4 Local and Remote addresses are
present.
o If length is 14, then the IPv4 Local address, IPv4 Remote address
and the MPLS SID are present.
o If length is 26, then the IPv4 Local address, IPv4 Remote address
and the IPv6 SID are present.
2.4.5.7. Type 7: IPv6 Address + index with optional SID
The Type-7 Segment Sub-TLV encodes an IPv6 node address, an interface
index and an optional SID in the form of either an MPLS label or an
IPv6 address. The format is 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IfIndex (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SID (optional, 4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: suggested value 7, to be assigned by IANA.
o Length is 22 or 26 or 38.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o IfIndex: 4 octets of interface index.
Previdi, et al. Expires May 3, 2017 [Page 18]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o IPv6 Node Address: a 16 octet IPv6 address representing a node.
o SID: either 4 octet MPLS SID or a 16 octet IPv6 address.
The following applies to the Type-7 Segment sub-TLV:
o The IPv6 Node Address MUST be present.
o The Interface Index MUST be present.
o The SID is optional and MAY be of one of the following formats:
* MPLS SID: a 4 octet label containing label, TC, S and TTL as
defined in Section 2.4.5.1.
* IPV6 SID: a 16 octet IPv6 address.
o If length is 22, then the IPv6 Node Address and IfIndex are
present.
o If length is 26, then the IPv6 Node Address, the IfIndex and the
MPLS SID are present.
o If length is 38, then the IPv6 Node Address, the IfIndex and the
IPv6 SID are present.
2.4.5.8. Type 8: IPv6 Local and Remote addresses with optional SID
The Type-8 Segment Sub-TLV encodes an IPv6 node address, an adjacency
local address, an adjacency remote address and an optional SID in the
form of either an MPLS label or an IPv6 address. The format is 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SID (4 or 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Previdi, et al. Expires May 3, 2017 [Page 19]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o Type: suggested value 8, to be assigned by IANA.
o Length is 34 or 38 or 50.
o Flags: 1 octet of flags. None is defined at this stage. Flags
SHOULD be unset on transmission and MUST be ignored on receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be unset on
transmission and MUST be ignored on receipt.
o Local IPv6 Address: a 16 octet IPv6 address.
o Remote IPv6 Address: a 16 octet IPv6 address.
o SID: either 4 octet MPLS SID or a 16 octet IPv6 address.
The following applies to the Type-8 Segment sub-TLV:
o The Local IPv6 Address MUST be present and represents an adjacency
local address.
o The Remote IPv6 Address MUST be present and represents the remote
end of the adjacency.
o The SID is optional and MAY be of one of the following formats:
* MPLS SID: a 4 octet label containing label, TC, S and TTL as
defined in Section 2.4.5.1.
* IPV6 SID: a 16 octet IPv6 address.
o If length is 34, then only the IPv6 Local and Remote addresses are
present.
o If length is 38, then the IPv6 Local address, IPv4 Remote address
and the MPLS SID are present.
o If length is 50, then the IPv6 Local address, IPv4 Remote address
and the IPv6 SID are present.
3. SR TE Policy Operations
3.1. Configuration and Advertisement of SR TE Policies
Typically, but not limited to, a SR TE Policy is configured into a
controller and on the base of each receiver. In other words, each SR
TE Policy configured is related to the intended receiver. It is
therefore normal for a given <color,endpoint> SR TE Policy to have
Previdi, et al. Expires May 3, 2017 [Page 20]
Internet-Draft Segment Routing TE Policies in BGP October 2016
multiple instances with different content (i.e.: different segment
lists) where each of these instances (of the same policy) is intended
to be sent to different receivers.
Each instance of the same SR TE Policy will have a different
Distinguisher in order to prevent BGP selection among these instances
along the distribution of BGP updates.
Moreover, a Route-Target extended community SHOULD be attached to the
SR TE Policy and that identifies the intended receiver of the
advertisement.
If no route-target is attached to the SR TE Policy NLRI, then it is
assumed that the originator sends the SR TE Policy update directly
(e.g.: through iBGP multihop) to the intended receiver. In such
case, the NO_ADVERTISE community MUST be attached to the SR TE Policy
update.
3.2. Multipath Operation
The SR TE Policy MAY contain multiple Segment Lists which, in the
absence of the Weight TLV, signifies equal cost load balancing
amongst them.
When a weight sub-TLV is encoded in each Segment List TLV, then the
weight value SHOULD be used in order to perform an unequal cost load
balance amongst the Segment Lists as specified in Section 2.4.3.
3.3. Binding SID TLV
When the optional Binding SID sub-TLV is present, it indicates an
instruction, to the receiving BGP speaker to allocate a Binding SID
for the list of SIDs the Binding sub-TLV is related to.
Any incoming packet with the Binding SID as active segment (according
to the terminology described in [I-D.ietf-spring-segment-routing])
will then have the Binding SID swapped with the list of SIDs
specified in the Segment List sub-TLVs on the allocating BGP speaker.
The allocated Binding SID MAY be then advertised by the BGP speaker
that created it, through, e.g., BGP-LS in order to, typically, feed a
controller with the updated topology and SR TE Policy information.
3.4. Reception of an SR TE Policy
On reception of a SR TE Policy, a BGP speaker MUST determine if the
SR TE Policy is first acceptable, then usable.
Previdi, et al. Expires May 3, 2017 [Page 21]
Internet-Draft Segment Routing TE Policies in BGP October 2016
While only usable SR TE Policies are instantiated, acceptable SR TE
Policies (i.e.: also the non-usable ones) MAY be propagated.
Any SR TE Policy update that has been determined acceptable is kept
in the BGP database. This includes non-usable SR TE Policies.
3.4.1. Acceptance of a SR TE Policy Update
When a BGP speaker receives an SR TE Policy from a neighbor it has to
determine if the SR TE Policy advertisement is acceptable. The
following applies:
o The SR TE Policy NLRI MUST have a color value and MUST have an
endpoint value.
o The SR TE Policy NLRI MUST have distinguisher field.
o The SR TE Policy update MUST have either the NO_ADV community or
at least one route-target extended community in IPv4-address
format.
o The Tunnel Encapsulation Attribute MUST be attached to the BGP
Update and MUST have the Tunnel Type set to SR TE Policy (value to
be assigned by IANA).
o Within the SR TE Policy, at least one Segment List sub-TLV MUST be
present.
o Within the Segment List sub-TLV at least one Segment sub-TLV MUST
be present.
The Remote Endpoint and Color sub-TLVs, as defined in
[I-D.ietf-idr-tunnel-encaps], MAY also be present in the SR TE Policy
encodings. If present, the Remote Endpoint sub-TLV MUST match the
Endpoint of the SR TE Policy SAFI NLRI. If they don't match, the SR
TE Policy advertisement MUST be considered as not acceptable. If
present, the Color sub-TLV MUST match the Policy Color of the SR TE
Policy SAFI NLRI. If they don't match, the SR TE Policy
advertisement MUST be considered as not acceptable.
A non-acceptable SR TE Policy update that has a valid NLRI portion
with invalid attribute portion MUST be considered as a withdraw of
the SR TE Policy.
A non-acceptable SR TE Policy update that has an invalid NLRI portion
MUST trigger a reset of the BGP session.
Previdi, et al. Expires May 3, 2017 [Page 22]
Internet-Draft Segment Routing TE Policies in BGP October 2016
3.4.2. Usable SR TE Policy
When the receiver has determined that the received SR TE Policy is
acceptable according to previous section, it has to determine if the
received SR TE Policy is usable.
The receiver MUST check whether route-target or NO_ADVERTISE
communities are attached to it. If no route-target is present and
the NO_ADVERTISE community is present, then the SR TE Policy is
usable.
If one or more route-targets are present, then at least one route-
target MUST match the BGP Identifier (BGP Router-ID) of the receiver
in order for the update to be considered usable. The BGP Identifier
is defined in [RFC4271] as a 4 octet IPv4 address. Therefore the
route-target extended community MUST be of the same format.
If one or more route-targets are present and no one matches the local
BGP router-ID, then, while the SR TE Policy is acceptable, the SR TE
Policy is not usable. It has to be noted that if the receiver has
been explicitly configured to do so, it MAY propagate the SR TE
Policy to its neighbors as defined in Section 3.4.4.
The following applies to usable SR TE Policies:
o Any segment sub-TLV of type 3 to 8 that is present in the segment
list MUST be either validated or resolved:
if the SID portion of the sub-TLV is present, then the segment
MUST be validated by the receiver. Validation consists of
verifying that the SID value is related to the network address.
if the SID portion of the sub-TLV is not present, then the
segment MUST be resolved by the receiver. Resolution consists
of taking from the receiver database (e.g.; from the link-state
or routing information base) that the SID value related to the
network address in the sub-TLV.
o The receiver MUST check the validity of the first SID of each
Segment List sub-TLV of the SR TE Policy. The first SID MUST be
known in the receiver local table either as a label (in the case
the SID encodes a label value) or as an IPv6 address.
o Any invalid segment of the segment list MUST cause an invalidation
of the whole segment list. However, the SR TE Policy is still
usable if at least one segment list is valid.
Previdi, et al. Expires May 3, 2017 [Page 23]
Internet-Draft Segment Routing TE Policies in BGP October 2016
o The receiver much keep track of the validated segment (i.e.: the
first segment and any segment encoded in Sub-TLV type 3 to 8). A
segment who failed validation may become valid after a network
event and vice versa. The receiver SHOULD keep the state of the
received SR TE Policies based on latest state of the segments
requires validation.
It has to be noted that an SR-TE policy may be received by a server
that is not a router, and that does not have the necessary state that
allows him to infer the next-hop from the first segment. In that
case, if the server needs to send a packet according to a particular
SR-TE policy, it SHOULD push on the label stack that the policy
specifies, and then send the packet to a default router (or default
gateway).
3.4.3. Instantiation of an SR TE Policy
On reception of an acceptable, valid and usable SR TE Policy, a BGP
speaker SHOULD instantiate the SR TE Policy in its routing and
forwarding table with the set of segment lists (i.e.: explicit paths)
included in the policy and taking into account the Binding SID and
Weight sub-TLVs.
The receiver of the SR TE Policy SHOULD program its MPLS or IPv6 data
planes so that BGP destination prefixes matching their Extended Color
Community and BGP next-hop with the SR TE Policy SAFI NLRI Color and
Endpoint are steered into the SR TE Policy and forwarded accordingly.
When building the MPLS label stack or the IPv6 Segment list from the
Segment List sub-TLV, the receiving BGP speaker MUST interpret the
set of Segment sub-TLVs as follows:
o The first Segment sub-TLV represents the topmost label or the
first IPv6 segment. In the receiving BGP speaker, it identifies
the first segment the traffic will be directed towards to (along
the SR TE explicit path).
o The last Segment sub-TLV represents the bottommost label or the
last IPv6 segment.
As described in Section 2.4.3, when present, the Weight sub-TLV
specifies a weight to be associated with the corresponding Segment
List, for use in unequal-cost multi path. Weights are applied by
summing the total value of all of the weights for all Segment Lists,
and then assigning a fraction of the forwarded traffic to each
Segment List in proportion its weight's fraction of the total.
Previdi, et al. Expires May 3, 2017 [Page 24]
Internet-Draft Segment Routing TE Policies in BGP October 2016
If in a SR TE Policy only some of the segment lists have a Weight
Sub-TLV present, then for those who haven't any weight, a value of 1
is assumed.
3.4.4. Propagation of an SR TE Policy
By default, a BGP node receiving an SR TE Policy MUST NOT not
propagate it to any eBGP neighbor.
However, a node MAY be explicitly configured in order to advertise a
received SR TE Policy update to neighbors according to normal BGP
rules (iBGP and eBGP propagation), e.g., in the case the node is a
Route-Reflector.
SR TE Policies that have been determined acceptable and valid can be
propagated, even the ones that are not usable.
Only SR TE Policies that do not have the NO_ADVERTISE community
attached to them can be propagated.
3.5. Steering Traffic into a SR TE Policy
The Color field of the NLRI allows association of destination
prefixes with a given SR TE Policy. The BGP speaker SHOULD then
attach a Color Extended Community (as defined in [RFC5512]) to
destination prefixes (e.g.: IPv4/IPv6 unicast prefixes) in order to
allow the receiver of the SR TE Policy and of the destination prefix
to steer traffic into the SR TE Policy if the destination prefix:
o Has a BGP next-hop matching the SR TE Policy SAFI NLRI Endpoint
and
o Has an attached Extended Color Community with the same value as
the color of the SR TE Policy NLRI Color.
On the receiving BGP speaker, all destination prefixes that share the
same Extended Color Community value and the same BGP next-hop are
steered to the corresponding SR TE Policy that has been instantiated
and which matches the Color and Endpoint NLRI values.
It is assumed that only one Extended Color Community is attached to a
destination prefix. In case a destination prefix is received with
multiple Extended Color Communities, the receiver MUST consider the
color corresponding to the SR TE Policy having the highest Preference
TLV value. In case of multiple policies having the same preference,
as a breaking tie, the router SHOULD select the policy having the
lowest color value.
Previdi, et al. Expires May 3, 2017 [Page 25]
Internet-Draft Segment Routing TE Policies in BGP October 2016
Different destination prefixes can be steered into distinct SR TE
Policies by coloring them differently.
3.6. Flowspec and SR TE Policies
The SR TE Policy can be carried in context of a Flowspec NLRI
([RFC5575]). In this case, when the redirect to IP next-hop is
specified as in [I-D.ietf-idr-flowspec-redirect-ip], the tunnel to
the next-hop is specified by the segment list in the Segment List
sub-TLVs. The Segment List (e.g..: label stack or IPv6 segment list)
is imposed to flows matching the criteria in the Flowspec route in
order to steer them towards the next-hop as specified in the SR TE
Policy SAFI NLRI.
4. Acknowledgments
The authors of this document would like to thank Dhanendra Jain,
Shyam Sethuram, Acee Lindem and Imtiyaz Mohammad for their comments
and review of this document.
5. IANA Considerations
This document defines:
o a new SAFI in the registry "Subsequent Address Family Identifiers
(SAFI) Parameters":
Suggested Description Reference
Value
-----------------------------------------------------
73 SR TE Policy SAFI This document
o a new Tunnel-Type in the registry "BGP Tunnel Encapsulation
Attribute Tunnel Types":
Suggested Description Reference
Value
-----------------------------------------------------
14 SR TE Policy Type This document
o new sub-TLVs in the registry "BGP Tunnel Encapsulation Attribute
sub-TLVs":
Previdi, et al. Expires May 3, 2017 [Page 26]
Internet-Draft Segment Routing TE Policies in BGP October 2016
Suggested Description Reference
Value
-----------------------------------------------------
6 Preference sub-TLV This document
7 Binding SID sub-TLV This document
8 Segment List sub-TLV This document
o A new registry called "SR TE Policy List Sub-TLVs" with following
codepoints:
Suggested Description Reference
Value
------------------------------------------------------------
1 MPLS SID This document
2 IPv6 SID This document
3 IPv4 Node and SID This document
4 IPv6 Node and SID This document
5 IPv4 Node, index and SID This document
6 IPv4 Local/Remote addresses and SID This document
7 IPv6 Node, index and SID This document
8 IPv6 Local/Remote addresses and SID This document
9 Weight sub-TLV This document
6. Security Considerations
TBD.
7. References
7.1. Normative References
[I-D.ietf-idr-tunnel-encaps]
Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel
Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-02
(work in progress), May 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
Previdi, et al. Expires May 3, 2017 [Page 27]
Internet-Draft Segment Routing TE Policies in BGP October 2016
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512,
DOI 10.17487/RFC5512, April 2009,
<http://www.rfc-editor.org/info/rfc5512>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
<http://www.rfc-editor.org/info/rfc5575>.
7.2. Informational References
[I-D.ietf-6man-segment-routing-header]
Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
J., Aries, E., Kosugi, T., Vyncke, E., and D. Lebrun,
"IPv6 Segment Routing Header (SRH)", draft-ietf-6man-
segment-routing-header-02 (work in progress), September
2016.
[I-D.ietf-idr-flowspec-redirect-ip]
Uttaro, J., Haas, J., Texier, M., Andy, A., Ray, S.,
Simpson, A., and W. Henderickx, "BGP Flow-Spec Redirect to
IP Action", draft-ietf-idr-flowspec-redirect-ip-02 (work
in progress), February 2015.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-09 (work in progress), July 2016.
[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Shakir, R.,
jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
with MPLS data plane", draft-ietf-spring-segment-routing-
mpls-05 (work in progress), July 2016.
Previdi, et al. Expires May 3, 2017 [Page 28]
Internet-Draft Segment Routing TE Policies in BGP October 2016
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
Authors' Addresses
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
Arjun Sreekantiah
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: asreekan@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: msiva@cisco.com
Previdi, et al. Expires May 3, 2017 [Page 29]
Internet-Draft Segment Routing TE Policies in BGP October 2016
Paul Mattes
Microsoft
One Microsoft Way
Redmond, WA 98052
USA
Email: pamattes@microsoft.com
Eric Rosen
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
US
Email: erosen@juniper.net
Steven Lin
Google
Email: stevenlin@google.com
Previdi, et al. Expires May 3, 2017 [Page 30]