Segment Routing Prefix Segment Identifier Extensions for BGPHuawei TechnologiesItalystefano@previdi.netCisco SystemsBrusselsBelgiumcfilsfil@cisco.comCisco Systems301 Midenhall WayCary, NCUnited States of America27513acee@cisco.comarjunhrs@gmail.comRtBrick Inc.hannes@rtbrick.com
Routing
IDRSRMPLSBGPPrefix-SIDLabel-IndexSRGBSegment Routing (SR) leverages the source-routing paradigm. A node
steers a packet through an ordered list of instructions called
"segments". A segment can represent any instruction, topological or
service based. The ingress node prepends an SR header to a packet
containing a set of segment identifiers (SIDs). Each SID represents a
topological or service-based instruction. Per-flow state is maintained
only on the ingress node of the SR domain. An "SR domain" is defined as a
single administrative domain for global SID assignment.This document defines an optional, transitive BGP attribute for
announcing information about BGP Prefix Segment Identifiers (BGP Prefix-SIDs)
and the specification for SR-MPLS SIDs.Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
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Table of Contents
. Introduction
. MPLS BGP Prefix-SID
. BGP Prefix-SID Attribute
. Label-Index TLV
. Originator SRGB TLV
. Receiving BGP Prefix-SID Attribute
. MPLS Data Plane: Labeled Unicast
. Advertising BGP Prefix-SID Attribute
. MPLS Data Plane: Labeled Unicast
. Error Handling of BGP Prefix-SID Attribute
. IANA Considerations
. Manageability Considerations
. Security Considerations
. References
. Normative References
. Informative References
Acknowledgements
Contributors
Authors' Addresses
IntroductionThe Segment Routing (SR) architecture leverages the source-routing
paradigm. A segment represents either a topological instruction, such as
"go to prefix P following shortest path", or a service instruction.
Other types of segments may be defined in the future.A segment is identified through a Segment Identifier (SID).
An "SR domain" is defined as a single administrative domain for
global SID assignment. It may be comprised of a single Autonomous System (AS)
or multiple ASes under consolidated global SID administration. Typically, the ingress
node of the SR domain prepends an SR header containing SIDs to an incoming packet.As described in ,
when SR is applied to the MPLS data plane (), the SID consists of a
label. also
describes how Segment Routing can be applied to an IPv6 data plane (SRv6) using
an IPv6 routing header containing a stack of SR SIDs encoded as
IPv6 addresses .
The applicability and support for Segment Routing over IPv6 is beyond the
scope of this document.A BGP Prefix Segment is a BGP prefix with a Prefix-SID attached.
A BGP Prefix-SID is always a global SID () within the SR domain
and identifies an instruction to forward
the packet over the Equal-Cost Multipath (ECMP) 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 Prefix Segment by the BGP
Prefix-SID.This document describes the BGP extensions to signal the BGP
Prefix-SID. Specifically, this document defines a BGP attribute
known as the "BGP Prefix-SID attribute" and specifies the rules to
originate, receive, and handle error conditions for the attribute.The BGP Prefix-SID attribute defined in this document can be attached
to prefixes from Multiprotocol BGP IPv4/IPv6 Labeled
Unicast ().
Usage of the BGP Prefix-SID attribute for other
Address Family Identifier (AFI) / Subsequent Address
Family Identifier (SAFI) combinations
is not defined herein but may be specified in
future specifications. describes
example use cases where the BGP Prefix-SID is used for the above
AFI/SAFI combinations.It should be noted that:
A BGP Prefix-SID will be global across ASes when the
interconnected ASes are part of the same SR domain.
Alternatively, when interconnecting ASes, 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.
A BGP Prefix-SID MAY be attached to a BGP prefix.
This implies that each prefix is advertised individually, reducing the
ability to pack BGP advertisements (when sharing common
attributes).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
MPLS BGP Prefix-SIDThe BGP Prefix-SID is realized on the MPLS data plane () in the following
way:
The operator
assigns a globally unique label index, L_I, to a locally originated
prefix of a BGP speaker N, which is advertised to all other BGP
speakers in the SR domain.
According to ,
each BGP speaker is configured with a label block called the
Segment Routing Global Block (SRGB). While recommends using 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 and .
If traffic engineering within the SR domain is required, each
node may also be required to advertise topological information and
Peer SIDs for each of its links and peers. This information is
required to perform the explicit path computation and to
express an explicit path as a list of SIDs. The advertisement
of topological information and peer segments (Peer SIDs) is done
through .
If a prefix segment is to be included in an MPLS label stack,
e.g., for traffic-engineering purposes, knowledge of the prefix
originator's SRGB is required in order to compute the local label used
by the originator.
This document assumes that Border Gateway Protocol - Link State
(BGP-LS) is the preferred method for a
collecting both peer segments (Peer SIDs) and SRGB
information through , , and . However, as an
optional alternative for the advertisement of the local SRGB
without the topology or the peer SIDs and, therefore, without
applicability for TE, the Originator SRGB TLV of the BGP Prefix-SID
attribute is specified in of this
document.
A BGP speaker will derive its local MPLS label L from the
label index L_I and its local SRGB as
described in . The
BGP speaker then programs the MPLS label L in its MPLS data plane as
its incoming/local label for the prefix.
See for more details.
The outgoing label for the prefix is found in the
Network Layer Reachability Information (NLRI) of the
Multiprotocol BGP IPv4/IPv6 Labeled Unicast prefix advertisement as
defined in .
The label index L_I is only used as a hint to derive the local/incoming
label.
of this document specifies the
Label-Index TLV of the BGP Prefix-SID attribute; this TLV can be
used to advertise the label index for a given prefix.
BGP Prefix-SID AttributeThe BGP Prefix-SID attribute is an optional, transitive BGP path
attribute. The attribute type code 40 has been assigned by IANA (see
).The BGP Prefix-SID attribute is defined here to be a set of elements
encoded as "Type/Length/Value" tuples (i.e., a set of TLVs). All BGP
Prefix-SID attribute TLVs will start with a 1-octet type and a 2-octet
length. The following TLVs are defined in this
document:
Label-Index TLV
Originator SRGB TLV
The Label-Index and Originator SRGB TLVs are used only when SR is applied
to the MPLS data plane.For future extensibility, unknown TLVs MUST be ignored and propagated
unmodified.Label-Index TLVThe Label-Index TLV MUST be present in the BGP Prefix-SID attribute
attached to IPv4/IPv6 Labeled Unicast prefixes (). It MUST be ignored when received for other
BGP AFI/SAFI combinations. The Label-Index TLV has the
following format: 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Label Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+where:
Type:
1
Length:
7, the total length in octets of the value portion
of the TLV.
RESERVED:
8-bit field. It MUST be clear on transmission and MUST be
ignored on reception.
Flags:
16 bits of flags. None are defined by this document. The
Flags field MUST be clear on transmission and MUST be ignored on
reception.
Label Index:
32-bit value representing the index value in the
SRGB space.
The total length in octets of the value portion of
the TLV: 2 + (non-zero multiple of 6).
Flags:
16 bits of flags. None are defined in this document.
The Flags field MUST be clear on transmission and MUST be ignored on
reception.
SRGB:
3 octets specifying the first label in the range followed
by 3 octets specifying the number of labels in the range. Note that
the SRGB field MAY appear multiple times. If the SRGB field
appears multiple times, the SRGB consists of multiple ranges
that are concatenated.
The Originator SRGB TLV contains the SRGB of the node originating
the prefix to which the BGP Prefix-SID is attached. The Originator
SRGB TLV MUST NOT be changed during the propagation of the BGP
update. It is used to build SR policies
when different SRGBs are used in the fabric, for example, .Examples of how the receiving routers concatenate the
ranges and build their neighbor's Segment Routing Global Block (SRGB)
are included in .The Originator SRGB TLV may only appear in a BGP Prefix-SID attribute
attached to IPv4/IPv6 Labeled Unicast prefixes (). It MUST be ignored when received for other
BGP AFI/SAFI combinations. Since the Label-Index TLV is required
for IPv4/IPv6 prefix applicability, the Originator SRGB TLV will be
ignored if it is not specified in a manner consistent with .If a BGP speaker receives a node's SRGB as an attribute of the BGP-LS
Node NLRI and the BGP speaker also receives the same node's SRGB
in a BGP Prefix-SID attribute, then the received values should be the
same. If the values are different, the values advertised in the BGP-LS
NLRI SHOULD be preferred, and an error should be logged.Receiving BGP Prefix-SID AttributeA BGP speaker receiving a BGP Prefix-SID attribute from an External BGP (EBGP)
neighbor residing outside the boundaries of the SR domain MUST
discard the attribute unless it is configured to accept the attribute
from the EBGP neighbor. A BGP speaker SHOULD log an error for further
analysis when discarding an attribute.MPLS Data Plane: Labeled UnicastA BGP session supporting the Multiprotocol BGP Labeled IPv4 or IPv6 Unicast () AFI/SAFI is required.When the BGP Prefix-SID attribute is attached to a BGP Labeled IPv4 or IPv6
Unicast AFI/SAFI, it 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 to be "invalid" by the
receiving speaker.The label index provides guidance to the receiving BGP speaker as to
the incoming label that SHOULD be allocated to the prefix.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.The mechanisms through which a given label-index value is assigned
to a given prefix are outside the scope of this document.Given a label index L_I, we refer to (L = L_I + SRGB_Start) as the
derived label. A BGP Prefix-SID attribute is designated "conflicting" for
a speaker M if the derived label value L lies outside the SRGB
configured on M. Otherwise, the Label-Index TLV is designated
"acceptable" to speaker M.If multiple different prefixes are received with the same label
index, all of the different prefixes MUST have
their BGP Prefix-SID attribute considered to be "conflicting".If multiple valid paths for the same prefix are received from
multiple BGP speakers or, in the case of ,
from the same BGP speaker, and the BGP Prefix-SID attributes do
not contain the same label index, then the label index from
the best path BGP Prefix-SID attribute SHOULD be chosen with
a notable exception being when
is being used to dampen route changes.When a BGP speaker receives a path from a neighbor with an
"acceptable" BGP Prefix-SID attribute and that path is selected as
the best path, it SHOULD program the derived label
as the label for the prefix in its local MPLS data plane.When a BGP speaker receives a path from a neighbor with an
"invalid" or "conflicting" BGP Prefix-SID attribute, or when a
BGP speaker receives a path from a neighbor with a BGP Prefix-SID
attribute but is unable to process it (e.g., local policy disables
the functionality), it MUST ignore the
BGP Prefix-SID attribute. For the purposes of label allocation, a
BGP speaker MUST assign a local (also called dynamic) label (non-SRGB)
for such a prefix as per classic Multiprotocol BGP IPv4/IPv6 Labeled
Unicast () operation.In the case of an "invalid" BGP Prefix-SID attribute, a BGP speaker MUST
follow the error-handling rules specified in .
A BGP speaker SHOULD log an error for further analysis. In the case of a
"conflicting" BGP Prefix-SID attribute, a BGP speaker SHOULD NOT treat it
as an error and SHOULD propagate the attribute unchanged. A BGP speaker SHOULD
log a warning for further analysis, i.e., in the case the conflict is
not due to a label-index transition.When a BGP Prefix-SID attribute changes and transitions from
"conflicting" to "acceptable", the BGP Prefix-SID attributes for other
prefixes may also transition to "acceptable" as well. Implementations SHOULD
ensure all impacted prefixes revert to using the label indices
corresponding to these newly "acceptable" BGP Prefix-SID attributes.The outgoing label is always programmed as per classic
Multiprotocol BGP IPv4/IPv6 Labeled Unicast ()
operation. Specifically, a BGP speaker receiving a prefix with a BGP Prefix-SID
attribute and a label NLRI field of Implicit NULL
from a neighbor MUST
adhere to standard behavior and program its MPLS data plane 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.Advertising BGP Prefix-SID AttributeThe BGP Prefix-SID attribute MAY be attached to BGP IPv4/IPv6 Labeled Unicast prefixes
. In order to prevent distribution of the BGP
Prefix-SID attribute beyond its intended scope of applicability,
attribute filtering SHOULD be deployed to remove the BGP
Prefix-SID attribute at the administrative boundary of the
SR domain.A BGP speaker that advertises a path received from one of its
neighbors SHOULD advertise the BGP Prefix-SID received with the path
without modification as long as the BGP Prefix-SID was acceptable.
If the path did not come with a BGP Prefix-SID attribute, the
speaker MAY attach a BGP Prefix-SID to the path if configured to do so.
The content of the TLVs present in the BGP Prefix-SID is determined by the
configuration.MPLS Data Plane: Labeled UnicastA BGP speaker that originates a prefix attaches the BGP Prefix-SID
attribute when it advertises the prefix to its neighbors via
Multiprotocol BGP IPv4/IPv6 Labeled Unicast (). The value of the label index in the Label-Index
TLV is determined by configuration.A BGP speaker that originates a BGP Prefix-SID attribute MAY optionally
announce the Originator SRGB TLV along with the mandatory Label-Index TLV.
The content of the Originator SRGB TLV is determined by
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 AS unless it is explicitly
configured to do so.In all cases, the Label field of the advertised NLRI () MUST be set to the
local/incoming label programmed in the MPLS data plane for the given
advertised prefix. If the prefix is associated with one of the BGP
speaker's interfaces, this is the usual MPLS label (such as the
Implicit or Explicit NULL label
).Error Handling of BGP Prefix-SID AttributeWhen a BGP speaker receives a BGP UPDATE message containing a
malformed or invalid BGP Prefix-SID attribute attached to an
IPv4/IPv6 Labeled Unicast prefix (), it MUST
ignore the received BGP Prefix-SID attribute and not advertise it to
other BGP peers. In this context, a malformed BGP Prefix-SID attribute
is one that cannot be parsed due to not meeting the minimum attribute
length requirement, containing a TLV length that doesn't conform to the
length constraints for the TLV, or containing a TLV length that would
extend beyond the end of the attribute (as defined by the attribute
length).
This is equivalent to the "Attribute discard"
action specified in . When discarding an
attribute, a BGP speaker SHOULD log an error for further analysis.As per , if the BGP
Prefix-SID attribute appears more than once in an UPDATE
message, all the occurrences of the attribute other than the
first one SHALL be discarded and the UPDATE message will continue
to be processed.
Similarly, if a recognized TLV appears more than once in a BGP
Prefix-SID attribute while the specification only allows for a single
occurrence, then all the occurrences of the TLV other than the
first one SHALL be discarded and the Prefix-SID attribute will continue
to be processed.For future extensibility, unknown TLVs MUST be ignored and
propagated unmodified.IANA ConsiderationsThis document defines a BGP path attribute known as the BGP
Prefix-SID attribute. IANA has assigned
attribute code type 40 to the BGP Prefix-SID
attribute from the "BGP Path Attributes" registry.This document defines two TLVs for the BGP Prefix-SID attribute. These
TLVs have been registered with IANA. IANA has created a
registry for BGP Prefix-SID Attribute TLVs as follows:Under the "Border Gateway Protocol (BGP) Parameters" registry, the new registry titled "BGP
Prefix-SID TLV Types" has been created and points to this
document as the reference.Registration Procedure(s):
Values 1-254, Expert Review as defined in
Values
0 and 255, Reserved
BGP Prefix-SID TLV Types
Value
Type
Reference
0
Reserved
This document
1
Label-Index
This document
2
Deprecated
This document
3
Originator SRGB
This document
4-254
Unassigned
255
Reserved
This document
The value 2 previously corresponded to the IPv6 SID TLV, which was specified
in previous versions of this document. It was removed, and use of
the BGP Prefix-SID for Segment Routing over the IPv6 data plane
has been deferred to
future specifications.IANA has also created the "BGP Prefix-SID Label-Index TLV Flags"
registry under the "Border Gateway Protocol (BGP) Parameters" registry,
with a reference to this document. Initially, this 16-bit flags registry is
empty. The registration policy for flag bits is Expert Review ,
consistent with the "BGP Prefix-SID TLV Types" registry.Finally, IANA has created the "BGP Prefix-SID Originator SRGB TLV Flags"
registry under the "Border Gateway Protocol (BGP) Parameters" registry,
with a reference to this document. Initially, this 16-bit flags registry is
empty. The registration policy for flag bits is Expert Review
consistent with the BGP Prefix-SID TLV Types registry.The designated experts must be good and faithful stewards of the above registries,
ensuring that each request is legitimate and corresponds to a viable use case. Given
the limited number of bits in the flags registries and the applicability to a single TLV,
additional scrutiny should be afforded to requests for flag-bit allocation. In general, no
single use case should require more than one flag bit and, should the use case
require more, alternate encodings using new TLVs should be considered.Manageability ConsiderationsThis document defines a BGP attribute to address use
cases such as the one described in
.
It is assumed that advertisement of the BGP Prefix-SID attribute is
controlled by the operator in order to:
Prevent undesired origination/advertisement of the BGP Prefix-SID
attribute. By default, a BGP Prefix-SID attribute SHOULD NOT be
attached to a prefix and advertised. Hence, BGP Prefix-SID
Advertisement SHOULD require explicit enablement.
Prevent any undesired propagation of the BGP Prefix-SID
attribute. By default, the BGP Prefix-SID is not advertised outside
the boundary of a single SR/administrative domain that may include
one or more ASes. The propagation to other ASes MUST be
explicitly configured.
The deployment model described in assumes multiple
ASes under a common administrative domain. For this
use case, the BGP Prefix-SID Advertisement is applicable to the inter-AS
context, i.e., EBGP, while it is confined to a single
administrative domain.Security ConsiderationsThis document introduces a BGP attribute (BGP Prefix-SID), which
inherits the security considerations expressed in: , , and
.When advertised using BGPsec as described in ,
the BGP Prefix-SID attribute doesn't impose any unique
security considerations. It should be noted that the BGP Prefix-SID
attribute is not protected by the BGPsec signatures.It should be noted that,
as described in , this document refers
to a deployment model where all nodes are under the single administrative domain.
In this context, we assume that the operator doesn't want to leak
any information related to internal prefixes and topology outside of the
administrative domain.
The internal information includes the BGP Prefix-SID. In order
to prevent such leaking, the common BGP mechanisms (filters) are
applied at the boundary of the SR/administrative domain.
Local BGP-attribute-filtering policies
and mechanisms are not standardized and, consequently, are beyond the
scope of this document.To prevent a Denial-of-Service (DoS) or Distributed-Denial-of-Service
(DDoS) attack due to excessive BGP updates with an invalid or conflicting
BGP Prefix-SID attribute, error log message rate limiting as well as suppression of
duplicate error log messages SHOULD be deployed.Since BGP-LS is the preferred method for advertising SRGB information,
the BGP speaker SHOULD log an error if a BGP Prefix-SID attribute
is received with SRGB information different from that received as an attribute of
the same node's BGP-LS Node NLRI.ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.A Border Gateway Protocol 4 (BGP-4)This document discusses the Border Gateway Protocol (BGP), which is an inter-Autonomous System routing protocol.The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the list of Autonomous Systems (ASes) that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability from which routing loops may be pruned, and, at the AS level, some policy decisions may be enforced.BGP-4 provides a set of mechanisms for supporting Classless Inter-Domain Routing (CIDR). These mechanisms include support for advertising a set of destinations as an IP prefix, and eliminating the concept of network "class" within BGP. BGP-4 also introduces mechanisms that allow aggregation of routes, including aggregation of AS paths.This document obsoletes RFC 1771. [STANDARDS-TRACK]BGP/MPLS IP Virtual Private Networks (VPNs)This document describes a method by which a Service Provider may use an IP backbone to provide IP Virtual Private Networks (VPNs) for its customers. This method uses a "peer model", in which the customers' edge routers (CE routers) send their routes to the Service Provider's edge routers (PE routers); there is no "overlay" visible to the customer's routing algorithm, and CE routers at different sites do not peer with each other. Data packets are tunneled through the backbone, so that the core routers do not need to know the VPN routes. [STANDARDS-TRACK]Multiprotocol Extensions for BGP-4This document defines extensions to BGP-4 to enable it to carry routing information for multiple Network Layer protocols (e.g., IPv6, IPX, L3VPN, etc.). The extensions are backward compatible - a router that supports the extensions can interoperate with a router that doesn't support the extensions. [STANDARDS-TRACK]Revised Error Handling for BGP UPDATE MessagesAccording to the base BGP specification, a BGP speaker that receives an UPDATE message containing a malformed attribute is required to reset the session over which the offending attribute was received. This behavior is undesirable because a session reset would impact not only routes with the offending attribute but also other valid routes exchanged over the session. This document partially revises the error handling for UPDATE messages and provides guidelines for the authors of documents defining new attributes. Finally, it revises the error handling procedures for a number of existing attributes.This document updates error handling for RFCs 1997, 4271, 4360, 4456, 4760, 5543, 5701, and 6368.Advertisement of Multiple Paths in BGPThis document defines a BGP extension that allows the advertisement of multiple paths for the same address prefix without the new paths implicitly replacing any previous ones. The essence of the extension is that each path is identified by a Path Identifier in addition to the address prefix.Guidelines for Writing an IANA Considerations Section in RFCsMany protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.This is the third edition of this document; it obsoletes RFC 5226.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.BGPsec Protocol SpecificationThis document describes BGPsec, an extension to the Border Gateway Protocol (BGP) that provides security for the path of Autonomous Systems (ASes) through which a BGP UPDATE message passes. BGPsec is implemented via an optional non-transitive BGP path attribute that carries digital signatures produced by each AS that propagates the UPDATE message. The digital signatures provide confidence that every AS on the path of ASes listed in the UPDATE message has explicitly authorized the advertisement of the route.Using BGP to Bind MPLS Labels to Address PrefixesThis document specifies a set of procedures for using BGP to advertise that a specified router has bound a specified MPLS label (or a specified sequence of MPLS labels organized as a contiguous part of a label stack) to a specified address prefix. This can be done by sending a BGP UPDATE message whose Network Layer Reachability Information field contains both the prefix and the MPLS label(s) and whose Next Hop field identifies the node at which said prefix is bound to said label(s). This document obsoletes RFC 3107.Segment Routing ArchitectureSegment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain.SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack.SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header.Segment Routing with the MPLS Data PlaneInformative ReferencesBGP-LS extensions for Segment Routing BGP Egress Peer EngineeringSegment Routing (SR) leverages source routing. A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. A segment can represent any instruction, topological or service-based. SR segments allow steering a flow through any topological path and service chain while maintaining per-flow state only at the ingress node of the SR domain. This document describes an extension to BGP Link-State (BGP-LS) for advertisement of BGP Peering Segments along with their BGP peering node information so that efficient BGP Egress Peer Engineering (EPE) policies and strategies can be computed based on Segment Routing.Work in ProgressBGP Link-State extensions for Segment RoutingSegment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by routing protocols e.g. by the link state routing protocols (IS-IS, OSPFv2 and OSPFv3) within IGP topologies. This document defines extensions to the BGP Link-state address-family in order to carry segment routing information via BGP.Work in ProgressIPv6 Segment Routing Header (SRH)Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header. This document describes the Segment Routing Header and how it is used by Segment Routing capable nodes.Work in ProgressMPLS Label Stack EncodingThis document specifies the encoding to be used by an LSR in order to transmit labeled packets on Point-to-Point Protocol (PPP) data links, on LAN data links, and possibly on other data links as well. This document also specifies rules and procedures for processing the various fields of the label stack encoding. [STANDARDS-TRACK]Avoid BGP Best Path Transitions from One External to AnotherIn this document, we propose an extension to the BGP route selection rules that would avoid unnecessary best path transitions between external paths under certain conditions. The proposed extension would help the overall network stability, and more importantly, would eliminate certain BGP route oscillations in which more than one external path from one BGP speaker contributes to the churn. [STANDARDS-TRACK]North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGPIn a number of environments, a component external to a network is called upon to perform computations based on the network topology and current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network.This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual IGP links. The mechanism described is subject to policy control.Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs).BGP Prefix Segment in Large-Scale Data CentersAcknowledgementsThe authors would like to thank Satya Mohanty for his contribution
to this document.The authors would like to thank Alvaro Retana for substantive
comments as part of the Routing AD review.The authors would like to thank Bruno Decraene for substantive
comments and suggested text as part of the Routing Directorate
review.The authors would like to thank Shyam Sethuram for comments and
discussion of TLV processing and validation.The authors would like to thank Robert Raszuk for comments and
suggestions regarding the MPLS data-plane behavior.The authors would like to thank Krishna Deevi,
Juan Alcaide, Howard Yang, and Jakob Heitz for discussions
on conflicting BGP Prefix-SID label indices and BGP add paths.The authors would like to thank Peter Yee, Tony Przygienda,
Mirja Kuhlewind, Alexey Melnikov, Eric Rescorla, Suresh
Krishnan, Warren Kumari, Ben Campbell Sue Hares, and Martin
Vigoureux for IDR Working Group last call, IETF Last Call,
directorate, and IESG reviews.ContributorsKeyur Patel
Arrcus, Inc.
United States of America
Email: Keyur@arrcus.comSaikat Ray
Unaffiliated
United States of America
Email: raysaikat@gmail.comAuthors' AddressesHuawei TechnologiesItalystefano@previdi.netCisco SystemsBrusselsBelgiumcfilsfil@cisco.comCisco Systems301 Midenhall WayCary, NCUnited States of America27513acee@cisco.comarjunhrs@gmail.comRtBrick Inc.hannes@rtbrick.com