--- 1/draft-ietf-idr-bgp-prefix-sid-04.txt 2017-04-20 03:13:08.222832636 -0700 +++ 2/draft-ietf-idr-bgp-prefix-sid-05.txt 2017-04-20 03:13:08.246832893 -0700 @@ -1,37 +1,34 @@ IDR S. Previdi, Ed. Internet-Draft C. Filsfils Intended status: Standards Track A. Lindem -Expires: June 15, 2017 K. Patel - A. Sreekantiah +Expires: October 22, 2017 A. Sreekantiah Cisco Systems - S. Ray - Unaffiliated H. Gredler RtBrick Inc. - December 12, 2016 + April 20, 2017 Segment Routing Prefix SID extensions for BGP - draft-ietf-idr-bgp-prefix-sid-04 + draft-ietf-idr-bgp-prefix-sid-05 Abstract Segment Routing (SR) architecture allows a node to steer a packet flow through any topological path and service chain by leveraging source routing. The ingress node prepends a SR header to a packet - containing a set of "segments". Each segment represents a + containing a set of segment identifiers (SID). Each SID represents a topological or a service-based instruction. Per-flow state is maintained only at the ingress node of the SR domain. This document describes the BGP extension for announcing BGP Prefix - Segment Identifier (BGP Prefix SID) information. + Segment Identifier (BGP Prefix-SID) information. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119] only when they appear in all upper case. They may also appear in lower or mixed case as English words, without any normative meaning. Status of This Memo @@ -41,224 +38,225 @@ 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 June 15, 2017. + This Internet-Draft will expire on October 22, 2017. Copyright Notice - Copyright (c) 2016 IETF Trust and the persons identified as the + Copyright (c) 2017 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. Segment Routing Documents . . . . . . . . . . . . . . . . . . 3 - 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 - 3. BGP-Prefix-SID . . . . . . . . . . . . . . . . . . . . . . . 4 - 3.1. MPLS Prefix Segment . . . . . . . . . . . . . . . . . . . 4 - 3.2. IPv6 Prefix Segment . . . . . . . . . . . . . . . . . . . 5 - 4. BGP-Prefix-SID Attribute . . . . . . . . . . . . . . . . . . 5 - 4.1. Label-Index TLV . . . . . . . . . . . . . . . . . . . . . 6 - 4.2. IPv6 SID . . . . . . . . . . . . . . . . . . . . . . . . 7 - 4.3. Originator SRGB TLV . . . . . . . . . . . . . . . . . . . 8 - 5. Receiving BGP-Prefix-SID Attribute . . . . . . . . . . . . . 9 - 5.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 9 - 5.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 10 - 6. Announcing BGP-Prefix-SID Attribute . . . . . . . . . . . . . 10 - 6.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 11 - 6.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 11 - 7. Error Handling of BGP-Prefix-SID Attribute . . . . . . . . . 12 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. BGP-Prefix-SID . . . . . . . . . . . . . . . . . . . . . . . 4 + 2.1. MPLS BGP Prefix SID . . . . . . . . . . . . . . . . . . . 4 + 2.2. IPv6 Prefix Segment . . . . . . . . . . . . . . . . . . . 5 + 3. BGP-Prefix-SID Attribute . . . . . . . . . . . . . . . . . . 5 + 3.1. Label-Index TLV . . . . . . . . . . . . . . . . . . . . . 6 + 3.2. IPv6 SID . . . . . . . . . . . . . . . . . . . . . . . . 7 + 3.3. Originator SRGB TLV . . . . . . . . . . . . . . . . . . . 7 + 4. Receiving BGP-Prefix-SID Attribute . . . . . . . . . . . . . 9 + 4.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 9 + 4.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 10 + 5. Announcing BGP-Prefix-SID Attribute . . . . . . . . . . . . . 10 + 5.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 10 + 5.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 11 + 6. Error Handling of BGP-Prefix-SID Attribute . . . . . . . . . 11 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 + 8. Manageability Considerations . . . . . . . . . . . . . . . . 12 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 - 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 - 11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 13 - 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 - 12.1. Normative References . . . . . . . . . . . . . . . . . . 13 - 12.2. Informative References . . . . . . . . . . . . . . . . . 13 + 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13 + 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 + 12.1. Normative References . . . . . . . . . . . . . . . . . . 14 + 12.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 -1. Segment Routing Documents - - The main references for this document are the SR architecture defined - in [I-D.ietf-spring-segment-routing] and the related use case - illustrated in [I-D.ietf-spring-segment-routing-msdc]. - - The Segment Routing Egress Peer Engineering architecture is described - in [I-D.ietf-spring-segment-routing-central-epe]. - - The Segment Routing Egress Peer Engineering BGPLS extensions are - described in [I-D.ietf-idr-bgpls-segment-routing-epe]. - -2. Introduction +1. Introduction Segment Routing (SR) architecture leverages the source routing paradigm. A group of inter-connected nodes that use SR forms a SR - domain. The ingress node of the SR domain prepends a SR header - containing "segments" to an incoming packet. Each segment represents - a topological instruction such as "go to prefix P following shortest - path" or a service instruction (e.g.: "pass through deep packet - inspection"). By inserting the desired sequence of instructions, the - ingress node is able to steer a packet via any topological path and/ - or service chain; per-flow state is maintained only at the ingress - node of the SR domain. + domain. A segment represents either a topological instruction such + as "go to prefix P following shortest path" or a service instruction + (e.g.: "pass through deep packet inspection"). Other types of + segments may be defined in the future. - Each segment is identified by a Segment Identifier (SID). As - described in [I-D.ietf-spring-segment-routing], when SR is applied to - the MPLS dataplane the SID consists of a label while when SR is - applied to the IPv6 dataplane the SID consists of an IPv6 prefix (see - [I-D.ietf-6man-segment-routing-header]). + A segment is identified through a Segment Identifier (SID). + Typically, the ingress node of the SR domain prepends a SR header + containing segments identifiers (SIDs) to an incoming packet. - A BGP-Prefix Segment (aka BGP-Prefix-SID), is a BGP segment attached - to a BGP prefix. A BGP-Prefix-SID is always global within the SR/BGP - domain and identifies an instruction to forward the packet over the - ECMP-aware best-path computed by BGP to the related prefix. The BGP- - Prefix-SID is the identifier of the BGP prefix segment. + As described in [I-D.ietf-spring-segment-routing], when SR is applied + to the MPLS dataplane ([I-D.ietf-spring-segment-routing-mpls]) the + SID consists of a label while when SR is applied to the IPv6 + dataplane the SID consists of an IPv6 address. - This document describes the BGP extension to signal the BGP-Prefix- + A BGP-Prefix Segment (and its BGP Prefix-SID), is a BGP segment + attached to a BGP prefix. A BGP Prefix-SID is always a global SID + ([I-D.ietf-spring-segment-routing]) within the SR/BGP domain (i.e., + the set of Autonomous Systems under a common administration and + control and where SR is used) and identifies an instruction to + forward the packet over the ECMP-aware best-path computed by BGP to + the related prefix. The BGP Prefix-SID is the identifier of the BGP + prefix segment. In this document we always refer to the BGP segment + as the BGP Prefix-SID. + + This document describes the BGP extension to signal the BGP Prefix- SID. Specifically, this document defines a new BGP attribute known - as the BGP Prefix SID attribute and specifies the rules to originate, + as the BGP Prefix-SID attribute and specifies the rules to originate, receive and handle error conditions of the new attribute. - As described in [I-D.ietf-spring-segment-routing-msdc], the newly - proposed BGP Prefix-SID attribute can be attached to prefixes from - AFI/SAFI: + As described in [I-D.ietf-spring-segment-routing-msdc], the BGP + Prefix-SID attribute defined in this document can be attached to + prefixes from AFI/SAFI: Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC3107]). Multiprotocol BGP ([RFC4760]) unlabeled IPv6 Unicast. [I-D.ietf-spring-segment-routing-msdc] describes use cases where the Prefix-SID is used for the above AFI/SAFI. -3. BGP-Prefix-SID + It has to be noted that: - The BGP-Prefix-SID attached to a BGP prefix P represents the + o A BGP Prefix-SID MAY be global between domains when the + interconnected domains agree on the SID allocation scheme. + + Alternatively, when interconnecting domains, the ASBRs of each + domain will have to handle the advertisement of unique SIDs. The + mechanisms for such interconnection are outside the scope of the + protocol extensions defined in this document. + + o As described in [I-D.ietf-spring-segment-routing-msdc], a BGP + Prefix-SID MAY be attached to a prefix. In addition, each prefix + will likely have a different as_path attribute. This implies that + each prefix is advertised individually, reducing the ability to + pack BGP advertisements (when sharing common attributes). + +2. BGP-Prefix-SID + + The BGP Prefix-SID attached to a BGP prefix P represents the instruction "go to Prefix P" along its BGP bestpath (potentially ECMP-enabled). -3.1. MPLS Prefix Segment +2.1. MPLS BGP Prefix SID - The BGP Prefix Segment is realized on the MPLS dataplane in the - following way: + The BGP Prefix-SID is realized on the MPLS dataplane + ([I-D.ietf-spring-segment-routing-mpls]) in the following way: As described in [I-D.ietf-spring-segment-routing-msdc] the operator assigns a globally unique "index", L_I, to a locally sourced prefix of a BGP speaker N which is advertised to all other BGP speakers in the SR domain. According to [I-D.ietf-spring-segment-routing], each BGP speaker is configured with a label block called the Segment Routing Global - Block (SRGB). While it is recommended to use the same SRGB across - all the nodes within the SR domain, the SRGB of a node is a local - property and could be different on different speakers. The - drawbacks of the use case where BGP speakers have different SRGBs - are documented in [I-D.ietf-spring-segment-routing] and + Block (SRGB). While [I-D.ietf-spring-segment-routing] recommends + to use the same SRGB across all the nodes within the SR domain, + the SRGB of a node is a local property and could be different on + different speakers. The drawbacks of the use case where BGP + speakers have different SRGBs are documented in + [I-D.ietf-spring-segment-routing] and [I-D.ietf-spring-segment-routing-msdc]. If traffic-engineering within the SR domain is required, each node may also be required to advertise topological information and - Peering SID's for each of its links and peers. This informations + Peering SID's for each of its links and peers. This information is required in order to perform the explicit path computation and - to express any explicit path into a list of segments. The - advertisement of topological information and Peer segments is - assumed to be done through + to express any explicit path into a list of SIDs. The + advertisement of topological information and Peer segments (Peer + SIDs) is assumed to be done through [I-D.ietf-idr-bgpls-segment-routing-epe]. If the BGP speakers are not all configured with the same SRGB, and if traffic-engineering within the SR domain is required, each node may be required to advertise its local SRGB in addition to the topological information. This documents assumes that BGP-LS is the preferred method for - collecting both topological, peer segments and SRGB information - through [RFC7752], [I-D.ietf-idr-bgpls-segment-routing-epe] and + collecting both topological, peer segments (Peer SIDs) and SRGB + information through [RFC7752], + [I-D.ietf-idr-bgpls-segment-routing-epe] and [I-D.ietf-idr-bgp-ls-segment-routing-ext]. However, as an optional alternative for the advertisement of the local SRGB without the topology nor the peer SID's, hence without applicability for TE, the Originator SRGB TLV of the prefix-SID - attribute, is specified in Section 4.3 of this document. + attribute, is specified in Section 3.3 of this document. - The index L_I is a 32 bit offset in the SRGB. Each BGP speaker - derives its local MPLS label, L, by adding L_I to the start value - of its own SRGB, and programs L in its MPLS dataplane as its - incoming/local label for the prefix. See Section 5.1 for more + As defined in [I-D.ietf-spring-segment-routing-mpls], the index + L_I is an offset in the SRGB. Each BGP speaker derives its local + MPLS label, L, by adding L_I to the start value of its own SRGB, + and programs L in its MPLS dataplane as its incoming/local label + for the prefix. It has to be noted that while SRGBs and SIDs are + advertised using 32 bit values, the derived label is to be + considered as the 20 right-most bits. See Section 4.1 for more details. The outgoing label for the prefix is found in the NLRI of the Multiprotocol BGP labeled IPv4/IPv6 Unicast prefix advertisement. The index L_I is only used as a hint to derive the local/incoming label. - Section 4.1 of this document specifies the Label-Index TLV of the + Section 3.1 of this document specifies the Label-Index TLV of the BGP Prefix-SID attribute; this TLV can be used to advertise the label index of a given prefix. In order to advertise the label index of a given prefix P and, optionally, the SRGB, a new extension to BGP is needed: the BGP - Prefix SID attribute. This extension is described in subsequent + Prefix-SID attribute. This extension is described in subsequent sections. -3.2. IPv6 Prefix Segment - - As defined in [I-D.ietf-6man-segment-routing-header], and as - illustrated in [I-D.ietf-spring-segment-routing-msdc], when SR is - used over an IPv6 dataplane, the BGP Prefix Segment is instantiated - by an IPv6 prefix originated by the BGP speaker. - - Each node advertises a globally unique IPv6 address representing - itself in the domain. This prefix (e.g.: its loopback interface - address) is advertised to all other BGP speakers in the SR domain. +2.2. IPv6 Prefix Segment - Also, each node MUST advertise its support of Segment Routing for - IPv6 dataplane. This is realized using the flags contained in the - Prefix SID Attribute defined below. + As illustrated in [I-D.ietf-spring-segment-routing-msdc], when SR is + used over an IPv6 dataplane, the BGP Prefix-SID consists of an IPv6 + address assigned to the BGP speaker. -4. BGP-Prefix-SID Attribute +3. BGP-Prefix-SID Attribute - The BGP Prefix SID attribute is an optional, transitive BGP path - attribute. The attribute type code is to be assigned by IANA - (suggested value: 40). The value field of the BGP-Prefix-SID - attribute has the following format: + The BGP Prefix-SID attribute is an optional, transitive BGP path + attribute. The attribute type code 40 has been assigned by IANA (see + Section 7). - The value field of the BGP Prefix SID attribute is defined here to be - a set of elements encoded as "Type/Length/Value" (i.e., a set of - TLVs). Following TLVs are defined: + The BGP Prefix-SID attribute is defined here to be a set of elements + encoded as "Type/Length/Value" (i.e., a set of TLVs). The following + TLVs are defined: o Label-Index TLV o IPv6 SID TLV o Originator SRGB TLV Label-Index and Originator SRGB TLVs are used only when SR is applied to the MPLS dataplane. IPv6 SID TLV is used only when SR is applied to the IPv6 dataplane. -4.1. Label-Index TLV +3.1. Label-Index TLV The Label-Index TLV MUST be present in the Prefix-SID attribute attached to Labeled IPv4/IPv6 unicast prefixes ([RFC3107]) 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ @@ -266,75 +264,62 @@ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: o Type is 1. o Length: is 7, the total length of the value portion of the TLV. - o RESERVED: 8 bit field. SHOULD be 0 on transmission and MUST be - ignored on reception. + o RESERVED: 8 bit field. MUST be clear on transmission an MUST be + ignored at reception.. - o Flags: 16 bits of flags. None are defined at this stage of the - document. The flag field SHOULD be clear on transmission and MUST - be ignored at reception. + o Flags: 16 bits of flags. None is defined by this document. The + flag field MUST be clear on transmission and MUST be ignored at + reception. o Label Index: 32 bit value representing the index value in the SRGB space. -4.2. IPv6 SID +3.2. IPv6 SID - The IPv6-SID TLV MUST be present in the Prefix-SID attribute attached + The IPv6-SID TLV MAY be present in the Prefix-SID attribute attached to MP-BGP unlabeled IPv6 unicast prefixes ([RFC4760]) 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | Flags | + | RESERVED | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | + | | + | IPv6 SID (16 octets) | + | | + | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: o Type is 2. - o Length: is 3, the total length of the value portion of the TLV. - - o RESERVED: 8 bit field. SHOULD be 0 on transmission and MUST be - ignored on reception. - - o Flags: 16 bits of flags defined as follow: - - 0 1 - 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - |S| | - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - where: + o Length: is 19, the total length of the value portion of the TLV. - * S flag: if set then it means that the BGP speaker attaching the - Prefix-SID Attribute to a prefix is capable of processing the - IPv6 Segment Routing Header (SRH, - [I-D.ietf-6man-segment-routing-header]) for the segment - corresponding to the originated IPv6 prefix. The use case - leveraging the S flag is described in - [I-D.ietf-spring-segment-routing-msdc]. + o RESERVED: 24 bit field for future use. MUST be clear on + transmission an MUST be ignored at reception. - The other bits of the flag field SHOULD be clear on transmission - an MUST be ignored at reception. + o IPv6 SID: 16 octets. -4.3. Originator SRGB TLV +3.3. Originator SRGB TLV The Originator SRGB TLV is an optional 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | @@ -352,136 +337,135 @@ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: o Type is 3. o Length is the total length of the value portion of the TLV: 2 + multiple of 6. - o Flags: 16 bits of flags. None are defined in this document. - Flags SHOULD be clear on transmission an MUST be ignored at - reception. + o Flags: 16 bits of flags. None is defined in this document. Flags + MUST be clear on transmission an MUST be ignored at reception. o SRGB: 3 octets of base followed by 3 octets of range. Note that the SRGB field MAY appear multiple times. If the SRGB field - appears multiple times, the SRGB consists of multiple ranges. The - meaning of an SRGB with multiple ranges is explained in - Section 3.2 ("SID/Label Range TLV") of - [I-D.ietf-ospf-segment-routing-extensions]. + appears multiple times, the SRGB consists of multiple ranges. - The Originator SRGB TLV contains the SRGB of the router originating - the prefix to which the BGP Prefix SID is attached and MUST be kept - in the Prefix-SID Attribute unchanged during the propagation of the - BGP update. + The Originator SRGB TLV contains the SRGB of the node originating the + prefix to which the BGP Prefix-SID is attached and MUST be kept in + the Prefix-SID Attribute unchanged during the propagation of the BGP + update. The originator SRGB describes the SRGB of the node where the BGP - Prefix Segment end. It is used to build SRTE policies when different - SRGB's are used in the fabric + Prefix SID is attached. It is used to build segment routing policies + when different SRGB's are used in the fabric ([I-D.ietf-spring-segment-routing-msdc]). The originator SRGB may only appear on Prefix-SID attribute attached to prefixes of SAFI 4 (labeled unicast, [RFC3107]). -5. Receiving BGP-Prefix-SID Attribute +4. Receiving BGP-Prefix-SID Attribute A BGP speaker receiving a BGP Prefix-SID attribute from an EBGP neighbor residing outside the boundaries of the SR domain, SHOULD discard the attribute unless it is configured to accept the attribute from the EBGP neighbor. A BGP speaker MAY log an error for further analysis when discarding an attribute. -5.1. MPLS Dataplane: Labeled Unicast +4.1. MPLS Dataplane: Labeled Unicast A Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC3107]) session type is required. - A BGP speaker may be locally configured with an SRGB=[GB_S, GB_E]. - The preferred method for deriving the SRGB is a matter of local - router configuration. + A BGP speaker MAY be locally configured with an SRGB=[SRGB_Start, + SRGB_End]. The preferred method for deriving the SRGB is a matter of + local node configuration. - Given a label index L_I, we call L = L_I + GB_S as the derived label. - A BGP Prefix-SID attribute is called "unacceptable" for a speaker M - if the derived label value L lies outside the SRGB configured on M. - Otherwise the Label Index attribute is called "acceptable" to speaker - M. + Given a label_index L_I, we call L = L_I + SRGB_Start as the derived + label. A BGP Prefix-SID attribute is called "unacceptable" for a + speaker M if the derived label value L lies outside the SRGB + configured on M. Otherwise the Label Index attribute is called + "acceptable" to speaker M. The mechanisms through which a given label_index value is assigned to a given prefix are outside the scope of this document. The label- index value associated with a prefix is locally configured at the BGP - router originating the prefix. + node originating the prefix. The Prefix-SID attribute MUST contain the Label-Index TLV and MAY contain the Originator SRGB TLV. A BGP Prefix-SID attribute received without a Label-Index TLV MUST be considered as "unacceptable" by the receiving speaker. + If multiple prefixes are received with the same label_index value, + all these prefixes MUST have their BGP Prefix-SID attribute + considered as "unacceptable" by the receiving speaker. + When a BGP speaker receives a path from a neighbor with an acceptable BGP Prefix-SID attribute, it MUST program the derived label as the local label for the prefix in its MPLS dataplane. In case of any error, a BGP speaker MUST resort to the error handling rules - specified in Section 7. A BGP speaker MAY log an error for further + specified in Section 6. A BGP speaker MAY log an error for further analysis. When a BGP speaker receives a path from a neighbor with an unacceptable BGP Prefix-SID attribute or when a BGP speaker receives - a path from a neighbor with a BGP-Prefix-SID attribute but is unable + a path from a neighbor with a BGP Prefix-SID attribute but is unable to process it (it does not have the capability or local policy disables the capability), it MUST treat the path as if it came without a Prefix-SID attribute. For the purposes of local label allocation, a BGP speaker MUST assign a local (also called dynamic) label (non-SRGB) for such a prefix as per classic Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC3107]) operation. A BGP speaker MAY log an error for further analysis. The outgoing label is always programmed as per classic Multiprotocol BGP labeled IPv4/IPv6 Unicast (RFC3107 [RFC3107]) operation. Specifically, a BGP speaker receiving a prefix with a Prefix-SID attribute and a label NLRI field of implicit-null from a neighbor MUST adhere to standard behavior and program its MPLS dataplane to pop the top label when forwarding traffic to the prefix. The label NLRI defines the outbound label that MUST be used by the receiving - node. The Label Index gives a hint to the receiving node on which - local/incoming label the BGP speaker SHOULD use. + node. The Label Index gives the information to the receiving node on + which local/incoming label the BGP speaker SHOULD use. -5.2. IPv6 Dataplane +4.2. IPv6 Dataplane - When a SR IPv6 BGP speaker receives a IPv6 Unicast BGP Update with a - prefix having the BGP Prefix SID attribute attached, it checks - whether the IPv6 SID TLV is present and if the S-flag is set. If the - IPv6 SID TLV is present and if the S-flag is not set, then the - Prefix-SID attribute MUST be considered as "unacceptable" by the - receiving speaker. + When an SR IPv6 BGP speaker receives a IPv6 Unicast BGP Update with a + prefix having the BGP Prefix-SID attribute attached, it checks + whether the IPv6 SID TLV is present. If present, then the receiver + assumes that the originator supports SR on the IPv6 dataplane. The Originator SRGB MUST be ignored on reception. A BGP speaker receiving a BGP Prefix-SID attribute from an EBGP neighbor residing outside the boundaries of the SR domain, SHOULD discard the attribute unless it is configured to accept the attribute from the EBGP neighbor. A BGP speaker MAY log an error for further analysis when discarding an attribute. -6. Announcing BGP-Prefix-SID Attribute +5. Announcing BGP-Prefix-SID Attribute The BGP Prefix-SID attribute MAY be attached to labeled BGP prefixes (IPv4/IPv6) [RFC3107]or to IPv6 prefixes [RFC4760]. In order to prevent distribution of the BGP Prefix-SID attribute beyond its - intended scope of applicability, attribute filtering MAY be deployed. + intended scope of applicability, attribute filtering SHOULD be + deployed. -6.1. MPLS Dataplane: Labeled Unicast +5.1. MPLS Dataplane: Labeled Unicast A BGP speaker that originates a prefix attaches the Prefix-SID attribute when it advertises the prefix to its neighbors via - Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC3107])The value of - the Label-Index in the Label-Index TLV is determined by + Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC3107]). The value + of the Label-Index in the Label-Index TLV is determined by configuration. A BGP speaker that originates a Prefix-SID attribute MAY optionally announce Originator SRGB TLV along with the mandatory Label-Index TLV. The content of the Originator SRGB TLV is determined by the configuration. Since the Label-index value must be unique within an SR domain, by default an implementation SHOULD NOT advertise the BGP Prefix-SID attribute outside an Autonomous System unless it is explicitly @@ -494,98 +478,152 @@ the speaker MAY attach a Prefix-SID to the path if configured to do so. The content of the TLVs present in the Prefix-SID is determined by the configuration. In all cases, the label field of the advertised NLRI ([RFC3107], [RFC4364]) MUST be set to the local/incoming label programmed in the MPLS dataplane for the given advertised prefix. If the prefix is associated with one of the BGP speakers interfaces, this label is the usual MPLS label (such as the implicit or explicit NULL label). -6.2. IPv6 Dataplane +5.2. IPv6 Dataplane - A BGP speaker that originates a prefix attaches the Prefix-SID - attribute when it advertises the prefix to its neighbors. The IPv6 - SID TLV MUST be present and the S-flag MUST be set. + A BGP speaker that originates an IPv6 prefix with the Prefix-SID + attribute, MAY include the IPv6 SID TLV. A BGP speaker that advertises a path received from one of its neighbors SHOULD advertise the Prefix-SID received with the path without modification regardless of whether the Prefix-SID was acceptable. If the path did not come with a Prefix-SID attribute, the speaker MAY attach a Prefix-SID to the path if configured to do - so. The IPv6-SID TLV MUST be present in the Prefix-SID and with the - S-flag set. + so. -7. Error Handling of BGP-Prefix-SID Attribute +6. Error Handling of BGP-Prefix-SID Attribute When a BGP Speaker receives a BGP Update message containing a malformed BGP Prefix-SID attribute, it MUST ignore the received BGP Prefix-SID attributes and not pass it to other BGP peers. This is equivalent to the -attribute discard- action specified in [RFC7606]. When discarding an attribute, a BGP speaker MAY log an error for further analysis. If the BGP Prefix-SID attribute appears more than once in an BGP Update message, then, according to [RFC7606], all the occurrences of the attribute other than the first one SHALL be discarded and the BGP - Update message shall continue to be processed. + Update message SHALL continue to be processed. When a BGP speaker receives an unacceptable Prefix-SID attribute, it MAY log an error for further analysis. -8. IANA Considerations +7. IANA Considerations This document defines a new BGP path attribute known as the BGP Prefix-SID attribute. This document requests IANA to assign a new attribute code type (suggested value: 40) for BGP the Prefix-SID attribute from the BGP Path Attributes registry. Currently, IANA temporarily assigned the following: 40 BGP Prefix-SID (TEMPORARY - registered 2015-09-30, expires 2016-09-30) [draft-ietf-idr-bgp-prefix-sid] This document defines 3 new TLVs for BGP Prefix-SID attribute. These TLVs need to be registered with IANA. We request IANA to create a new registry for BGP Prefix-SID Attribute TLVs as follows: Under "Border Gateway Protocol (BGP) Parameters" registry, "BGP - Prefix SID attribute Types" Reference: draft-ietf-idr-bgp-prefix-sid + Prefix-SID attribute Types" Reference: draft-ietf-idr-bgp-prefix-sid Registration Procedure(s): Values 1-254 First Come, First Served, Value 0 and 255 reserved Value Type Reference 0 Reserved this document 1 Label-Index this document 2 IPv6 SID this document 3 Originator SRGB this document 4-254 Unassigned 255 Reserved this document +8. Manageability Considerations + + This document defines a new BGP attribute in order to address the use + case described in [I-D.ietf-spring-segment-routing-msdc]. It i + assumed that the new attribute (BGP Prefix-SID) advertisement is + controlled by the operator in order to: + + o prevent undesired origination/advertisement of the BGP Prefix-SID + attribute. By default, a BGP Prefix-SID attribute SHOULD NOT be + originated and attached to a prefix. The operator MUST be capable + of explicitly enabling the BGP Prefix-SID origination. + + o Prevent any undesired propagation of the BGP Prefix-SID attribute. + By default the BGP Prefix-SID is not advertised outside the + boundary of an AS. The propagation to other ASs MUST be + explicitly configured. + + The deployment model described in + [I-D.ietf-spring-segment-routing-msdc] assumes multiple Autonomous + Systems (AS) under a common administration. The BGP Prefix-SID + advertisement is therefore applicable to inter-AS context while it is + confined within a single SR Domain. + 9. Security Considerations - This document introduces no new security considerations above and - beyond those already specified in [RFC4271] and [RFC3107]. + This document introduces a new BGP attribute (BGP Prefix-SID) which + inherits the security considerations expressed in: [RFC4271] and + [RFC3107]. -10. Acknowledgements + The BGP Prefix-SID attribute addresses the requirements introduced in + [I-D.ietf-spring-segment-routing-msdc] and It has to be noted, as + described in Section 8, that this document refer to a deployment + model where all nodes are under the same administration. In this + context, we assume that the operator doesn't want to leak outside of + the domain any information related to internal prefixes and topology. + The internal information includes the BGP Prefix-SID. In order to + prevent such leaking, the standard BGP mechanisms (filters) are + applied on the boundary of the domain. - The authors would like to thanks Satya Mohanty for his contribution - to this document. +10. Contributors -11. Change Log + Keyur Patel + Arrcus, Inc. + US - Initial Version: Sep 21 2014 + Email: Keyur@arrcus.com + + Saikat Ray + Unaffiliated + US + + Email: raysaikat@gmail.com + +11. Acknowledgements + + The authors would like to thanks Satya Mohanty for his contribution + to this document. 12. References 12.1. Normative References + [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-11 (work in progress), February + 2017. + + [I-D.ietf-spring-segment-routing-mpls] + Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., + Litkowski, S., and R. Shakir, "Segment Routing with MPLS + data plane", draft-ietf-spring-segment-routing-mpls-08 + (work in progress), March 2017. + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A @@ -597,62 +635,37 @@ Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, . [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. Patel, "Revised Error Handling for BGP UPDATE Messages", RFC 7606, DOI 10.17487/RFC7606, August 2015, . 12.2. Informative 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-bgp-ls-segment-routing-ext] Previdi, S., Psenak, P., Filsfils, C., Gredler, H., Chen, M., and j. jefftant@gmail.com, "BGP Link-State extensions for Segment Routing", draft-ietf-idr-bgp-ls-segment- - routing-ext-00 (work in progress), November 2016. + routing-ext-01 (work in progress), February 2017. [I-D.ietf-idr-bgpls-segment-routing-epe] - Previdi, S., Filsfils, C., Ray, S., Patel, K., Dong, J., + Previdi, S., Filsfils, C., Patel, K., Ray, S., Dong, J., and M. Chen, "Segment Routing BGP Egress Peer Engineering BGP-LS Extensions", draft-ietf-idr-bgpls-segment-routing- - epe-06 (work in progress), November 2016. - - [I-D.ietf-ospf-segment-routing-extensions] - Psenak, P., Previdi, S., Filsfils, C., Gredler, H., - Shakir, R., Henderickx, W., and J. Tantsura, "OSPF - Extensions for Segment Routing", draft-ietf-ospf-segment- - routing-extensions-10 (work in progress), October 2016. - - [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-10 (work in progress), November - 2016. - - [I-D.ietf-spring-segment-routing-central-epe] - Filsfils, C., Previdi, S., Aries, E., and D. Afanasiev, - "Segment Routing Centralized BGP Peer Engineering", draft- - ietf-spring-segment-routing-central-epe-03 (work in - progress), November 2016. + epe-11 (work in progress), March 2017. [I-D.ietf-spring-segment-routing-msdc] Filsfils, C., Previdi, S., Mitchell, J., Aries, E., and P. Lapukhov, "BGP-Prefix Segment in large-scale data - centers", draft-ietf-spring-segment-routing-msdc-02 (work - in progress), October 2016. + centers", draft-ietf-spring-segment-routing-msdc-04 (work + in progress), March 2017. [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, @@ -667,43 +680,30 @@ Italy Email: sprevidi@cisco.com Clarence Filsfils Cisco Systems Brussels Belgium Email: cfilsfils@cisco.com - Acee Lindem Cisco Systems 170 W. Tasman Drive San Jose, CA 95124 95134 USA Email: acee@cisco.com - Keyur Patel - Cisco Systems - 170 W. Tasman Drive - San Jose, CA 95124 95134 - USA - - Email: keyupate@cisco.com Arjun Sreekantiah Cisco Systems 170 W. Tasman Drive San Jose, CA 95124 95134 USA Email: asreekan@cisco.com - Saikat Ray - Unaffiliated - - Email: raysaikat@gmail.com - Hannes Gredler RtBrick Inc. Email: hannes@rtbrick.com