| Network Working Group | S. Previdi, Ed. |
| Internet-Draft | Individual |
| Intended status: Standards Track | C. Filsfils |
| Expires: November 21, 2019 | Cisco Systems, Inc. |
| D. Jain, Ed. | |
| P. Mattes | |
| Microsoft | |
| E. Rosen | |
| Juniper Networks | |
| S. Lin | |
| May 20, 2019 |
Advertising Segment Routing Policies in BGP
draft-ietf-idr-segment-routing-te-policy-06
This document defines a new BGP SAFI with a new NLRI in order to advertise a candidate path of a Segment Routing Policy (SR Policy). An SR Policy is a set of candidate paths, each consisting of one or more segment lists. The headend of an SR Policy may learn multiple candidate paths for an SR Policy. Candidate paths may be learned via a number of different mechanisms, e.g., CLI, NetConf, PCEP, or BGP. This document specifies the way in which BGP may be used to distribute candidate paths. New sub-TLVs for the Tunnel Encapsulation Attribute are defined.
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 https://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 November 21, 2019.
Copyright (c) 2019 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 (https://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.
Segment Routing (SR) allows a headend node to steer a packet flow along any path. Intermediate per-flow states are eliminated thanks to source routing [I-D.ietf-spring-segment-routing].
The headend node is said to steer a flow into a Segment Routing Policy (SR Policy).
The header of a packet steered in an SR Policy is augmented with the ordered list of segments associated with that SR Policy.
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR Policy and steering into an SR Policy. These apply equally to the MPLS and SRv6 instantiations of segment routing.
[I-D.filsfils-spring-sr-policy-considerations] describes some of the implementation aspects of the SR Policy Headend Architecture and introduces the notion of an SR Policy Module (SRPM) that performs the functionality as highlighted in section 2 of [I-D.ietf-spring-segment-routing-policy]:
This document specifies the way to use BGP to distribute one or more of the candidate paths of an SR Policy to the headend of that policy. The document identifies the functionality that resides in the BGP process and for the functionality which is outside the scope of BGP and lies within SRPM on the headend node, it refers to such, as appropriate.
This document specifies a way of representing SR Policies and their candidate paths in BGP UPDATE messages. BGP can then be used to propagate the SR Policies and candidate paths. The usual BGP rules for BGP propagation and "bestpath selection" are used. At the headend of a specific policy, this will result in one or more candidate paths being installed into the "BGP table". These paths are then passed to the SRPM. The SRPM may compare them to candidate paths learned via other mechanisms, and will choose one or more paths to be installed in the data plane. BGP itself does not install SR Policy candidate paths into the data plane.
This document defines a new BGP address family (SAFI). In UPDATE messages of that address family, the NLRI identifies an SR Policy, and the attributes encode the segment lists and other details of that SR Policy.
While for simplicity we may write that BGP advertises an SR Policy, it has to be understood that BGP advertises a candidate path of an SR policy and that this SR Policy might have several other candidate paths provided via BGP (via an NLRI with a different distinguisher as defined in this document), PCEP, NETCONF or local policy configuration.
Typically, a controller defines the set of policies and advertise them to policy head-end 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 a specific policy head-end. In this case the advertisement may sent on a BGP session to that head-end and not propagated any further.
Alternatively, a router (i.e., a BGP egress router) advertises SR Policies representing paths to itself. In this case, it is possible to send the policy to each head-end over a BGP session to that head-end, without requiring any further propagation of the policy.
An SR Policy intended only for the receiver will, in most cases, not traverse any Route Reflector (RR, [RFC4456]).
In some situations, it is undesirable for a controller or BGP egress router to have a BGP session to each policy head-end. In these situations, BGP Route Reflectors may be used to propagate the advertisements, or it may be necessary for the advertisement to propagate through a sequence of one or more ASes. To make this possible, an attribute needs to be attached to the advertisement that enables a BGP speaker to determine whether it is intended to be a head-end for the advertised policy. This is done by attaching one or more Route Target Extended Communities to the advertisement ([RFC4360]).
The BGP extensions for the advertisement of SR Policies include following components:
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.
A new SAFI is defined: the SR Policy SAFI, (codepoint 73 assigned by IANA (see Section 8) from the "Subsequent Address Family Identifiers (SAFI) Parameters" registry).
+------------------+ | NLRI Length | 1 octet +------------------+ | Distinguisher | 4 octets +------------------+ | Policy Color | 4 octets +------------------+ | Endpoint | 4 or 16 octets +------------------+ where:
The SR Policy SAFI uses a new NLRI defined as follows:
The color and endpoint are used to automate the steering of BGP Payload prefixes on SR Policy as described in [I-D.ietf-spring-segment-routing-policy].
The NLRI containing the SR 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 (assigned by IANA from the "Subsequent Address Family Identifiers (SAFI) Parameters" registry).
An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI attribute with the SR 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 network address field in SR Policy SAFI (73) updates may be either a 4 octet IPv4 address or a 16 octet IPv6 address, independent of the SR Policy AFI. The length field of the next-hop address specifies the next-hop address family. If the next-hop length is 4, then the next-hop is an IPv4 address; if the next-hop length is 16, then it is a global IPv6 address; and if the next-hop length is 32, then it has a global IPv6 address followed by a link-local IPv6 address. The setting of the next-hop field and its attendant processing is governed by standard BGP procedures as described in section 3 in [RFC4760].
It is important to note that any BGP speaker receiving a BGP message with an SR Policy NLRI, will process it only if the NLRI is among the best paths as per the BGP best path selection algorithm. In other words, this document does not modify the BGP propagation or bestpath selection rules.
It has to be noted that if several candidate paths of the same SR Policy (endpoint, color) are signaled via BGP to a head-end, it is recommended that each NLRI use a different distinguisher. If BGP has installed into the BGP table two advertisements whose respective NLRIs have the same color and endpoint, but different distinguishers, both advertisements are passed to the SRPM as different candidate paths. In addition, the originator information corresponding to the each candidate path, as described in section 2.4 in [I-D.ietf-spring-segment-routing-policy], is passed to the SRPM.
The content of the SR Policy is encoded in the Tunnel Encapsulation Attribute originally defined in [I-D.ietf-idr-tunnel-encaps] using a new Tunnel-Type TLV (codepoint is 15, assigned by IANA (see Section 8) from the "BGP Tunnel Encapsulation Attribute Tunnel Types" registry).
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
where:
The SR Policy Encoding structure is as follows:
A Tunnel Encapsulation Attribute MUST NOT contain more than one TLV of type "SR Policy". If more than one TLV of type "SR Policy" appears, the update is considered malformed and the "treat-as-withdraw" strategy of [RFC7606] is applied.
Multiple occurrences of "Segment List" MAY be encoded within the same SR Policy.
Multiple occurrences of "Segment" MAY be encoded within the same Segment List.
The Remote Endpoint and Color sub-TLVs, as defined in [I-D.ietf-idr-tunnel-encaps], MAY also be present in the SR Policy encodings.
The Remote Endpoint and Color Sub-TLVs are not used for SR Policy encodings and therefore their value is irrelevant in the context of the SR Policy SAFI NLRI. If present, the Remote Endpoint sub-TLV and the Color sub-TLV MUST be ignored by the BGP speaker.
This section defines the SR Policy sub-TLVs.
Preference, Binding SID, Segment-List, Priority, Policy Name and Explicit NULL Label Policy sub-TLVs are assigned from the "BGP Tunnel Encapsulation Attribute Sub-TLVs" registry.
Weight and Segment sub-TLVs are assigned from a new registry defined in this document and called: "SR Policy List Sub-TLVs". See Section 8 for the details of the registry.
The Preference sub-TLV does not have any effect on the BGP bestpath selection or propagation procedures. The contents of this sub-TLV are used by the SRPM as described in section 2.7 in [I-D.ietf-spring-segment-routing-policy].
The Preference sub-TLV is optional and it MUST NOT appear more than once in the SR Policy. If the Preference sub-TLV appears more than once, the update is considered malformed and the "treat-as-withdraw" strategy of [RFC7606] is applied.
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:
The Preference sub-TLV has following format:
The Binding SID sub-TLV is not used by BGP. The contents of this sub-TLV are used by the SRPM as described in section 6 in [I-D.ietf-spring-segment-routing-policy].
The Binding SID sub-TLV is optional and it MUST NOT appear more than once in the SR Policy. If the Binding SID sub-TLV appears more than once, the update is considered malformed and the "treat-as-withdraw" strategy of [RFC7606] is applied.
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:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S|I| |
+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Binding SID sub-TLV has the following format:
The Segment List sub-TLV encodes a single explicit path towards the endpoint as described in section 5.1 in [I-D.ietf-spring-segment-routing-policy]. The Segment List sub-TLV includes the elements of the paths (i.e., segments) as well as an optional Weight sub-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 codepoint defines the size of the length field. Therefore, for the Segment List sub-TLV a code point of 128 (or higher) is used. See Section 8 for details of codepoints allocation.
The Segment List sub-TLV is optional and MAY appear multiple times in the SR Policy. The ordering of Segment List sub-TLVs, each sub-TLV encoding a Segment List, does not matter.
The Segment List sub-TLV contains zero or more Segment sub-TLVs and MAY contain a Weight sub-TLV.
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:
The Segment List sub-TLV has the following format:
Validation of an explicit path encoded by the Segment List sub-TLV is completely within the scope of SRPM as described in section 5 in [I-D.ietf-spring-segment-routing-policy].
The Weight sub-TLV specifies the weight associated to a given segment list. The contents of this sub-TLV are used only by the SRPM as described in section 2.11 in [I-D.ietf-spring-segment-routing-policy].
The Weight sub-TLV is optional and it MUST NOT appear more than once inside the Segment List sub-TLV. If the Weight sub-TLV appears more than once, the update is considered malformed and the "treat-as-withdraw" strategy of [RFC7606] is applied.
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:
The Weight sub-TLV has the following format:
Type: 9 (to be assigned by IANA from the registry "SR Policy List Sub-TLVs" defined in this document).
Length: 6.
Flags: 1 octet of flags. None are defined at this stage. Flags SHOULD be set to zero on transmission and MUST be ignored on receipt.
RESERVED: 1 octet of reserved bits. SHOULD be unset on transmission and MUST be ignored on receipt.
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 Policy.
The Segment sub-TLV is optional and MAY appear multiple times in the Segment List sub-TLV.
The Segment sub-TLV does not have any effect on the BGP bestpath selection or propagation procedures. The contents of this sub-TLV are used only by the SRPM as described in section 4 in [I-D.ietf-spring-segment-routing-policy].
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 for SR MPLS Type 5: IPv4 Address + index with optional SID Type 6: IPv4 Local and Remote addresses with optional SID Type 7: IPv6 Address + index for local and remote pair with optional SID for SR MPLS Type 8: IPv6 Local and Remote addresses with optional SID for SR MPLS Type 9: IPv6 Node Address with optional SID for SRv6 Type 10: IPv6 Address + index for local and remote pair with optional SID for SRv6 Type 11: IPv6 Local and Remote addresses for SRv6
[I-D.ietf-spring-segment-routing-policy] defines several types of Segments:
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:
The Type-1 Segment Sub-TLV encodes a single SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-1 Segment sub-TLV:
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // SRv6 SID (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-2 Segment Sub-TLV encodes a single SRv6 SID in the form of an IPv6 address. The format is as follows:
The IPv6 Segment Identifier (SRv6 SID) is defined in [I-D.ietf-6man-segment-routing-header].
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 | SR Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Node Address (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (optional, 4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-3 Segment Sub-TLV encodes an IPv4 node address, SR Algorithm and an optional SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-3 Segment sub-TLV:
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 | SR Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IPv6 Node Address (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (optional, 4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-4 Segment Sub-TLV encodes an IPv6 node address, SR Algorithm and an optional SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-4 Segment sub-TLV:
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 Interface ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Node Address (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (optional, 4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-5 Segment Sub-TLV encodes an IPv4 node address, a local interface Identifier (Local Interface ID) and an optional SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-5 Segment sub-TLV:
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 (optional, 4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-6 Segment Sub-TLV encodes an adjacency local address, an adjacency remote address and an optional SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-6 Segment sub-TLV:
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 Interface ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IPv6 Local Node Address (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote Interface ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IPv6 Remote Node Address (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (optional, 4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-7 Segment Sub-TLV encodes an IPv6 Link Local adjacency with IPv6 local node address, a local interface identifier (Local Interface ID), IPv6 remote node address , a remote interface identifier (Remote Interface ID) and an optional SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-7 Segment sub-TLV:
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 (optional, 4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-8 Segment Sub-TLV encodes an adjacency local address, an adjacency remote address and an optional SID in the form of an MPLS label. The format is as follows:
The following applies to the Type-8 Segment sub-TLV:
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 | SR Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IPv6 Node Address (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // SID (optional, 16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-9 Segment Sub-TLV encodes an IPv6 node address, SR Algorithm and an optional SID in the form of an IPv6 address. The format is as follows:
The following applies to the Type-9 Segment sub-TLV:
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 Interface ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IPv6 Local Node Address (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote Interface ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // IPv6 Remote Node Address (16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // SID (optional, 16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-10 Segment Sub-TLV encodes an IPv6 Link Local adjacency with local node address, a local interface identifier (Local Interface ID), remote IPv6 node address , a remote interface identifier (Remote Interface ID) and an optional SID in the form of an IPv6 address. The format is as follows:
The following applies to the Type-10 Segment sub-TLV:
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 (optional, 16 octets) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where:
The Type-11 Segment Sub-TLV encodes an adjacency local address, an adjacency remote address and an optional SID in the form of IPv6 address. The format is as follows:
The following applies to the Type-11 Segment sub-TLV:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|A| |
+-+-+-+-+-+-+-+-+
The Segment Types described above MAY contain following flags in the "Flags" field (codes to be assigned by IANA from the registry "SR Policy Segment Flags" defined in this document Section 8.6):
The following applies to the Segment Flags:
In order to steer an unlabeled IP packet into an SR policy, it is necessary to create a label stack for that packet, and to push one or more labels onto that stack.
The Explicit NULL Label Policy sub-TLV is used to indicate whether an Explicit NULL Label [RFC3032] must be pushed on an unlabeled IP packet before any other labels.
If an Explicit NULL Label Policy Sub-TLV is not present, the decision of whether to push an Explicit NULL label on a given packet is a matter of local policy.
The contents of this sub-TLV are used by the SRPM as described in section 4.1 in [I-D.ietf-spring-segment-routing-policy].
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ENLP | +-+-+-+-+-+-+-+-+
Where:
An operator MAY set the Policy Priority sub-TLV to indicate the order in which the SR policies are re-computed upon topological change.
The Priority sub-TLV does not have any effect on the BGP bestpath selection or propagation procedures. The contents of this sub-TLV are used by the SRPM as described in section 2.11 in [I-D.ietf-spring-segment-routing-policy].
The Priority sub-TLV is optional and it MUST NOT appear more than once in the SR Policy TLV. If the Priority sub-TLV appears more than once, the update is considered malformed and the "treat-as-withdraw" strategy of [RFC7606] is applied.
The Priority sub-TLV 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 | Priority | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
An operator MAY set the Policy Name sub-TLV to attach a symbolic name to the SR Policy candidate path.
Usage of Policy Name sub-TLV is described in section 2 in [I-D.ietf-spring-segment-routing-policy].
The Policy Name sub-TLV may exceed 255 bytes length due to long policy name. Therefore a 2-octet length is required. According to [I-D.ietf-idr-tunnel-encaps], the first bit of the sub-TLV codepoint defines the size of the length field. Therefore, for the Policy Name sub-TLV a code point of 128 (or higher) is used. See Section 8 for details of codepoints allocation.
The Policy Name sub-TLV is optional and it MUST NOT appear more than once in the SR Policy TLV. If the Policy Name sub-TLV appears more than once, the update is considered malformed and the "treat-as-withdraw" strategy of [RFC7606] is applied.
The Policy Name sub-TLV 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 | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Policy Name // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
The Color Extended Community as defined in [I-D.ietf-idr-tunnel-encaps] is used to steer traffic into a policy.
1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |C O| RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the Color Extended Community is used for the purpose of steering the traffic into an SR Policy, the RESERVED field (as defined in [I-D.ietf-idr-tunnel-encaps] is changed as follows:[I-D.ietf-spring-segment-routing-policy] defines the influence of these bits on the automated steering of BGP Payload traffic onto SR Policies.
As described in this document, the consumer of an SR Policy NLRI is not the BGP process. The BGP process is in charge of the origination and propagation of the SR Policy NLRI but its installation and use is outside the scope of BGP. The details of SR Policy installation and use can be referred from [I-D.ietf-spring-segment-routing-policy].
Typically, but not limited to, an SR Policy is configured into a controller.
Multiple SR Policy NLRIs may be present with the same <color, endpoint> tuple but with different content when these SR policies are intended to different head-ends.
The distinguisher of each SR Policy NLRI prevents undesired BGP route selection among these SR Policy NLRIs and allow their propagation across route reflectors [RFC4456].
Moreover, one or more route-target SHOULD be attached to the advertisement, where each route-target identifies one or more intended head-ends for the advertised SR policy.
If no route-target is attached to the SR Policy NLRI, then it is assumed that the originator sends the SR Policy update directly (e.g., through a BGP session) to the intended receiver. In such case, the NO_ADVERTISE community MUST be attached to the SR Policy update.
On reception of an SR Policy NLRI, a BGP speaker MUST determine if it's first acceptable, then it determines if it is usable.
When a BGP speaker receives an SR Policy NLRI from a neighbor it has to determine if it's acceptable. The following applies:
A router that receives an SR Policy update that is not valid according to these criteria MUST treat the update as malformed. The route MUST NOT be passed to the SRPM, and the "treat-as-withdraw" strategy of [RFC7606] is applied.
A unacceptable SR Policy update that has a valid NLRI portion with invalid attribute portion MUST be considered as a withdraw of the SR Policy.
If one or more route-targets are present, then at least one route-target MUST match one of the BGP Identifiers 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 any of the local BGP Identifiers, then, while the SR Policy NLRI is acceptable, it is not usable on the receiver node. It has to be noted that if the receiver has been explicitly configured to do so, it MAY propagate the SR Policy NLRI to its neighbors as defined in Section 4.2.4.
The SR Policy candidate paths encoded by the usable SR Policy NLRIs are sent to the SRPM.
Once BGP has determined that the SR Policy NLRI is usable, BGP passes the SR Policy candidate path to the SRPM. Note that, along with the candidate path details, BGP also passes the originator information for breaking ties in the path-selection process as described in section 2.4 in [I-D.ietf-spring-segment-routing-policy].
The SRPM applies the rules defined in section 2 in [I-D.ietf-spring-segment-routing-policy] to determine whether the SR Policy candidate path is valid and to select the best candidate path among the valid SR Policy candidate paths.
By default, a BGP node receiving an SR Policy NLRI MUST NOT propagate it to any EBGP neighbor.
However, a node MAY be explicitly configured to advertise a received SR Policy NLRI to neighbors according to normal BGP rules (i.e., EBGP propagation by an ASBR or iBGP propagation by a Route-Reflector).
SR Policy NLRIs that have been determined acceptable and valid can be propagated, even the ones that are not usable.
Only SR Policy NLRIs that do not have the NO_ADVERTISE community attached to them can be propagated.
The SR 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 to steer them towards the next-hop as specified in the SR Policy SAFI NLRI.
Arjun Sreekantiah Cisco Systems US Email: asreekan@cisco.com
Acee Lindem Cisco Systems US Email: acee@cisco.com
Siva Sivabalan Cisco Systems US Email: msiva@cisco.com
Imtiyaz Mohammad Arista Networks India Email: imtiyaz@arista.com
Gaurav Dawra Cisco Systems US Email: gdawra.ietf@gmail.com
The authors of this document would like to thank Shyam Sethuram, John Scudder, Przemyslaw Krol, Alex Bogdanov, Nandan Saha and Ketan Talaulikar for their comments and review of this document.
Note to RFC Editor: Please remove this section prior to publication, as well as the reference to RFC 7942.
This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.
According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".
Several early implementations exist and will be reported in detail in a forthcoming version of this document. For purposes of early interoperability testing, when no FCFS code point was available, implementations have made use of the following values:
When IANA-assigned values are available, implementations will be updated to use them.
This document defines new Sub-TLVs in following existing registries:
This document also defines following new registries:
Codepoint Description Reference ----------------------------------------------- 73 SR Policy SAFI This document
This document defines a new SAFI in the registry "Subsequent Address Family Identifiers (SAFI) Parameters" that has been assigned by IANA:
Codepoint Description Reference -------------------------------------------------- 15 SR Policy Type This document
This document defines a new Tunnel-Type in the registry "BGP Tunnel Encapsulation Attribute Tunnel Types" that has been assigned by IANA:
Codepoint Description Reference ------------------------------------------------------ 12 Preference sub-TLV This document 13 Binding SID sub-TLV This document 128 Segment List sub-TLV This document TBD1 ENLP sub-TLV This document TBD2 Priority sub-TLV This document TBD3 Policy Name sub-TLV This document
This document defines new sub-TLVs in the registry "BGP Tunnel Encapsulation Attribute sub-TLVs" to be assigned by IANA:
This document defines a new registry called "SR Policy List Sub-TLVs". The allocation policy of this registry is "First Come First Served (FCFS)" according to [RFC8126].
Value Description Reference
---------------------------------------------------------------------------------
1 MPLS SID sub-TLV This document
2 SRv6 SID sub-TLV This document
3 IPv4 Node and SID sub-TLV This document
4 IPv6 Node and SID for SR-MPLS sub-TLV This document
5 IPv4 Node, index and SID sub-TLV This document
6 IPv4 Local/Remote addresses and SID sub-TLV This document
7 IPv6 Node, index for remote and local pair This document
and SID for SR-MPLS sub-TLV
8 IPv6 Local/Remote addresses and SID sub-TLV This document
9 Weight sub-TLV This document
10 IPv6 Node and SID for SRv6 sub-TLV This document
11 IPv6 Node, index for remote and local pair This document
and SID for SRv6 sub-TLV
12 IPv6 Local/Remote addresses and SID for This document
SRv6 sub-TLV
Following Sub-TLV codepoints are defined:
This document defines a new registry called "SR Policy Binding SID Flags". The allocation policy of this registry is "First Come First Served (FCFS)" according to [RFC8126].
Bit Description Reference --------------------------------------------------------------------------------- 0 Specified-BSID-Only Flag (S-Flag) This document 1 Drop Upon Invalid Flag (I-Flag) This document 2-7 Unassigned
Following Flags are defined:
This document defines a new registry called "SR Policy Segment Flags". The allocation policy of this registry is "First Come First Served (FCFS)" according to [RFC8126].
Bit Description Reference --------------------------------------------------------------------------------- 0 Segment Verification Flag (V-Flag) This document 1 SR Algorithm Flag (A-Flag) This document 2-7 Unassigned
Following Flags are defined:
TBD.
| [I-D.ietf-idr-tunnel-encaps] | Patel, K., Velde, G., Ramachandra, S. and E. Rosen, "The BGP Tunnel Encapsulation Attribute", Internet-Draft draft-ietf-idr-tunnel-encaps-12, May 2019. |
| [I-D.ietf-pce-segment-routing] | Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W. and J. Hardwick, "PCEP Extensions for Segment Routing", Internet-Draft draft-ietf-pce-segment-routing-16, March 2019. |
| [I-D.ietf-spring-segment-routing] | Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", Internet-Draft draft-ietf-spring-segment-routing-15, January 2018. |
| [I-D.ietf-spring-segment-routing-policy] | Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d., bogdanov@google.com, b. and P. Mattes, "Segment Routing Policy Architecture", Internet-Draft draft-ietf-spring-segment-routing-policy-03, May 2019. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3032] | Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T. and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001. |
| [RFC4271] | Rekhter, Y., Li, T. and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006. |
| [RFC4360] | Sangli, S., Tappan, D. and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February 2006. |
| [RFC4760] | Bates, T., Chandra, R., Katz, D. and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007. |
| [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. |
| [RFC7606] | Chen, E., Scudder, J., Mohapatra, P. and K. Patel, "Revised Error Handling for BGP UPDATE Messages", RFC 7606, DOI 10.17487/RFC7606, August 2015. |
| [RFC8126] | Cotton, M., Leiba, B. and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017. |
| [I-D.filsfils-spring-sr-policy-considerations] | Filsfils, C., Talaulikar, K., Krol, P., Horneffer, M. and P. Mattes, "SR Policy Implementation and Deployment Considerations", Internet-Draft draft-filsfils-spring-sr-policy-considerations-03, April 2019. |
| [I-D.ietf-6man-segment-routing-header] | Filsfils, C., Previdi, S., Leddy, J., Matsushima, S. and d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header (SRH)", Internet-Draft draft-ietf-6man-segment-routing-header-18, April 2019. |
| [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", Internet-Draft draft-ietf-idr-flowspec-redirect-ip-02, February 2015. |
| [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. |
| [RFC7942] | Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016. |