draft-ietf-lsvr-bgp-spf-00.txt   draft-ietf-lsvr-bgp-spf-01.txt 
Network Working Group K. Patel Network Working Group K. Patel
Internet-Draft Arrcus, Inc. Internet-Draft Arrcus, Inc.
Intended status: Standards Track A. Lindem Intended status: Standards Track A. Lindem
Expires: December 1, 2018 Cisco Systems Expires: December 2, 2018 Cisco Systems
S. Zandi S. Zandi
Linkedin Linkedin
W. Henderickx W. Henderickx
Nokia Nokia
May 30, 2018 May 31, 2018
Shortest Path Routing Extensions for BGP Protocol Shortest Path Routing Extensions for BGP Protocol
draft-ietf-lsvr-bgp-spf-00.txt draft-ietf-lsvr-bgp-spf-01.txt
Abstract Abstract
Many Massively Scaled Data Centers (MSDCs) have converged on Many Massively Scaled Data Centers (MSDCs) have converged on
simplified layer 3 routing. Furthermore, requirements for simplified layer 3 routing. Furthermore, requirements for
operational simplicity have lead many of these MSDCs to converge on operational simplicity have lead many of these MSDCs to converge on
BGP as their single routing protocol for both their fabric routing BGP as their single routing protocol for both their fabric routing
and their Data Center Interconnect (DCI) routing. This document and their Data Center Interconnect (DCI) routing. This document
describes a solution which leverages BGP Link-State distribution and describes a solution which leverages BGP Link-State distribution and
the Shortest Path First algorithm similar to Internal Gateway the Shortest Path First (SPF) algorithm similar to Internal Gateway
Protocols (IGPs) such as OSPF. Protocols (IGPs) such as OSPF.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 1, 2018. This Internet-Draft will expire on December 2, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2.1. BGP Single-Hop Peering on Network Node Connections . . . 5 2.1. BGP Single-Hop Peering on Network Node Connections . . . 5
2.2. BGP Peering Between Directly Connected Network Nodes . . 5 2.2. BGP Peering Between Directly Connected Network Nodes . . 5
2.3. BGP Peering in Route-Reflector or Controller Topology . . 6 2.3. BGP Peering in Route-Reflector or Controller Topology . . 6
3. BGP-LS Shortest Path Routing (SPF) SAFI . . . . . . . . . . . 6 3. BGP-LS Shortest Path Routing (SPF) SAFI . . . . . . . . . . . 6
4. Extensions to BGP-LS . . . . . . . . . . . . . . . . . . . . 6 4. Extensions to BGP-LS . . . . . . . . . . . . . . . . . . . . 6
4.1. Node NLRI Usage and Modifications . . . . . . . . . . . . 7 4.1. Node NLRI Usage and Modifications . . . . . . . . . . . . 7
4.2. Link NLRI Usage . . . . . . . . . . . . . . . . . . . . . 7 4.2. Link NLRI Usage . . . . . . . . . . . . . . . . . . . . . 7
4.3. Prefix NLRI Usage . . . . . . . . . . . . . . . . . . . . 8 4.3. Prefix NLRI Usage . . . . . . . . . . . . . . . . . . . . 8
4.4. BGP-LS Attribute Sequence-Number TLV . . . . . . . . . . 8 4.4. BGP-LS Attribute Sequence-Number TLV . . . . . . . . . . 8
5. Decision Process with SPF Algorithm . . . . . . . . . . . . . 9 5. Decision Process with SPF Algorithm . . . . . . . . . . . . . 9
5.1. Phase-1 BGP NLRI Selection . . . . . . . . . . . . . . . 9 5.1. Phase-1 BGP NLRI Selection . . . . . . . . . . . . . . . 10
5.2. Dual Stack Support . . . . . . . . . . . . . . . . . . . 10 5.2. Dual Stack Support . . . . . . . . . . . . . . . . . . . 10
5.3. NEXT_HOP Manipulation . . . . . . . . . . . . . . . . . . 10 5.3. NEXT_HOP Manipulation . . . . . . . . . . . . . . . . . . 11
5.4. IPv4/IPv6 Unicast Address Family Interaction . . . . . . 11 5.4. IPv4/IPv6 Unicast Address Family Interaction . . . . . . 11
5.5. NLRI Advertisement and Convergence . . . . . . . . . . . 11 5.5. NLRI Advertisement and Convergence . . . . . . . . . . . 11
5.6. Error Handling . . . . . . . . . . . . . . . . . . . . . 11 5.6. Error Handling . . . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Acknowledgements . . . . . . . . . . . . . . . . . . . . 12 7.1. Acknowledgements . . . . . . . . . . . . . . . . . . . . 12
7.2. Contributors . . . . . . . . . . . . . . . . . . . . . . 12 7.2. Contributors . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Information References . . . . . . . . . . . . . . . . . 14 8.2. Information References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
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[RFC4271] defines the Decision Process that is used to select routes [RFC4271] defines the Decision Process that is used to select routes
for subsequent advertisement by applying the policies in the local for subsequent advertisement by applying the policies in the local
Policy Information Base (PIB) to the routes stored in its Adj-RIBs- Policy Information Base (PIB) to the routes stored in its Adj-RIBs-
In. The output of the Decision Process is the set of routes that are In. The output of the Decision Process is the set of routes that are
announced by a BGP speaker to its peers. These selected routes are announced by a BGP speaker to its peers. These selected routes are
stored by a BGP speaker in the speaker's Adj-RIBs-Out according to stored by a BGP speaker in the speaker's Adj-RIBs-Out according to
policy. policy.
[RFC7752] describes a mechanism by which link-state and TE [RFC7752] describes a mechanism by which link-state and TE
information can be collected from networks and shared with external information can be collected from networks and shared with external
components using BGP. This is achieved by defining NLRI carried components using BGP. This is achieved by defining NLRI advertised
within BGP-LS AFI and BGP-LS SAFIs. The BGP-LS extensions defined in within the BGP-LS/BGP-LS-SPF AFI/SAFI. The BGP-LS extensions defined
[RFC7752] makes use of the Decision Process defined in [RFC4271]. in [RFC7752] makes use of the Decision Process defined in [RFC4271].
This document augments [RFC7752] by replacing its use of the existing This document augments [RFC7752] by replacing its use of the existing
Decision Process. The BGP-LS-SPF and BGP-LS-SPF-VPN AFI/SAFI are Decision Process. Rather than reusing the BGP-LS SAFI, the BGP-LS-
introduced to insure backward compatibility. The Phase 1 and 2 SPF SAFI is introduced to insure backward compatibility. The Phase 1
decision functions of the Decision Process are replaced with the and 2 decision functions of the Decision Process are replaced with
Shortest Path Algorithm (SPF) also known as the Dijkstra Algorithm. the Shortest Path First (SPF) algorithm also known as the Dijkstra
The Phase 3 decision function is also simplified since it is no algorithm. The Phase 3 decision function is also simplified since it
longer dependent on the previous phases. This solution avails the is no longer dependent on the previous phases. This solution avails
benefits of both BGP and SPF-based IGPs. These include TCP based the benefits of both BGP and SPF-based IGPs. These include TCP based
flow-control, no periodic link-state refresh, and completely flow-control, no periodic link-state refresh, and completely
incremental NLRI advertisement. These advantages can reduce the incremental NLRI advertisement. These advantages can reduce the
overhead in MSDCs where there is a high degree of Equal Cost Multi- overhead in MSDCs where there is a high degree of Equal Cost Multi-
Path (ECMPs) and the topology is very stable. Additionally, using a Path (ECMPs) and the topology is very stable. Additionally, using a
SPF-based computation can support fast convergence and the SPF-based computation can support fast convergence and the
computation of Loop-Free Alternatives (LFAs) [RFC5286] in the event computation of Loop-Free Alternatives (LFAs) [RFC5286] in the event
of link failures. Furthermore, a BGP based solution lends itself to of link failures. Furthermore, a BGP based solution lends itself to
multiple peering models including those incorporating route- multiple peering models including those incorporating route-
reflectors [RFC4456] or controllers. reflectors [RFC4456] or controllers.
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Given that [RFC7938] already describes how BGP could be used as the Given that [RFC7938] already describes how BGP could be used as the
sole routing protocol in an MSDC, one might question the motivation sole routing protocol in an MSDC, one might question the motivation
for defining an alternate BGP deployment model when a mature solution for defining an alternate BGP deployment model when a mature solution
exists. For both alternatives, BGP offers the operational benefits exists. For both alternatives, BGP offers the operational benefits
of a single routing protocol. However, BGP SPF offers some unique of a single routing protocol. However, BGP SPF offers some unique
advantages above and beyond standard BGP distance-vector routing. advantages above and beyond standard BGP distance-vector routing.
A primary advantage is that all BGP speakers in the BGP SPF routing A primary advantage is that all BGP speakers in the BGP SPF routing
domain will have a complete view of the topology. This will allow domain will have a complete view of the topology. This will allow
support of ECMP, IP fast-reroute (e.g., Loop-Free Alternatives), support for ECMP, IP fast-reroute (e.g., Loop-Free Alternatives),
Shared Risk Link Groups (SRLGs), and other routing enhancements Shared Risk Link Groups (SRLGs), and other routing enhancements
without advertisement of addition BGP paths or other extensions. In without advertisement of addition BGP paths or other extensions. In
short, the advantages of an IGP such as OSPF [RFC2328] are availed in short, the advantages of an IGP such as OSPF [RFC2328] are availed in
BGP. BGP.
With the simplified BGP decision process as defined in Section 5.1, With the simplified BGP decision process as defined in Section 5.1,
NLRI changes can be disseminated throughout the BGP routing domain NLRI changes can be disseminated throughout the BGP routing domain
much more rapidly (equivalent to IGPs with the proper much more rapidly (equivalent to IGPs with the proper
implementation). implementation).
Another primary advantage is a potential reduction in NLRI Another primary advantage is a potential reduction in NLRI
advertisement. With standard BGP distance-vector routing, a single advertisement. With standard BGP distance-vector routing, a single
link failure may impact 100s or 1000s prefixes and result in the link failure may impact 100s or 1000s prefixes and result in the
withdrawal or re-advertisement of the attendant NLRI. With BGP SPF, withdrawal or re-advertisement of the attendant NLRI. With BGP SPF,
only the BGP speakers corresponding to the link NLRI need withdraw only the BGP speakers corresponding to the link NLRI need withdraw
the corresponding BGP-LS Link NLRI. This advantage will contribute the corresponding BGP-LS Link NLRI. This advantage will contribute
to both faster convergence and better scaling. to both faster convergence and better scaling.
With controller and route-reflector peering models, BGP SPF With controller and route-reflector peering models, BGP SPF
advertisement and distributed computation require a minimal number of advertisement and distributed computation require a minimal number of
sessions and copies of the NLRI since only the latest verion of the sessions and copies of the NLRI since only the latest version of the
NLRI from the originator is required. Given that verification of the NLRI from the originator is required. Given that verification of the
adjacencies is done outside of BGP (see Section 2), each BGP speaker adjacencies is done outside of BGP (see Section 2), each BGP speaker
will only need as many sessions and copies of the NLRI as required will only need as many sessions and copies of the NLRI as required
for redundancy (e.g., one for SPF computation and another for for redundancy (e.g., one for the SPF computation and another for
backup). Functions such as Optimized Route Reflection (ORR) are backup). Functions such as Optimized Route Reflection (ORR) are
supported without extension by virture of the primary advantages. supported without extension by virtue of the primary advantages.
Additionally, a controller could inject topology that is learned Additionally, a controller could inject topology that is learned
outside the BGP routing domain. outside the BGP routing domain.
Given that controllers are already consuming BGP-LS NLRI [RFC7752], Given that controllers are already consuming BGP-LS NLRI [RFC7752],
reusing for the BGP-LS SPF leverages the existing controller reusing for the BGP-LS SPF leverages the existing controller
implementations. implementations.
Another potential advantage of BGP SPF is that both IPv6 and IPv4 can Another potential advantage of BGP SPF is that both IPv6 and IPv4 can
be supported in the same address family using the same topology. be supported in the same address family using the same topology.
Although not described in this version of the document, multi- Although not described in this version of the document, multi-
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unicast, and multicast topologies while sharing the same NLRI. unicast, and multicast topologies while sharing the same NLRI.
Finally, the BGP SPF topology can be used as an underlay for other Finally, the BGP SPF topology can be used as an underlay for other
BGP address families (using the existing model) and realize all the BGP address families (using the existing model) and realize all the
above advantages. A simplified peering model using IPv6 link-local above advantages. A simplified peering model using IPv6 link-local
addresses as next-hops can be deployed similar to [RFC5549]. addresses as next-hops can be deployed similar to [RFC5549].
1.2. Requirements Language 1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. BGP Peering Models 2. BGP Peering Models
Depending on the requirements, scaling, and capabilities of the BGP Depending on the requirements, scaling, and capabilities of the BGP
speakers, various peering models are supported. The only requirement speakers, various peering models are supported. The only requirement
is that all BGP speakers in the BGP SPF routing domain receive link- is that all BGP speakers in the BGP SPF routing domain receive link-
state NLRI on a timely basis, run an SPF calculation, and update state NLRI on a timely basis, run an SPF calculation, and update
their data plane appropriately. The content of the Link NLRI is their data plane appropriately. The content of the Link NLRI is
described in Section 4.2. described in Section 4.2.
2.1. BGP Single-Hop Peering on Network Node Connections 2.1. BGP Single-Hop Peering on Network Node Connections
The simplest peering model is the one described in section 5.2.1 of The simplest peering model is the one described in section 5.2.1 of
[RFC7938]. In this model, EBGP single-hop sessions are established [RFC7938]. In this model, EBGP single-hop sessions are established
over direct point-to-point links interconnecting the network nodes. over direct point-to-point links interconnecting the SPF domain
For the purposes of BGP SPF, Link NLRI is only advertised if a nodes. For the purposes of BGP SPF, Link NLRI is only advertised if
single-hop BGP session has been established and the Link-State/SPF a single-hop BGP session has been established and the Link-State/SPF
adddress family capability has been exchanged [RFC4790] on the address family capability has been exchanged [RFC4790] on the
corresponding session. If the session goes down, the NLRI will be corresponding session. If the session goes down, the corresponding
withdrawn. Link NLRI will be withdrawn.
2.2. BGP Peering Between Directly Connected Network Nodes 2.2. BGP Peering Between Directly Connected Network Nodes
In this model, BGP speakers peer with all directly connected network In this model, BGP speakers peer with all directly connected network
nodes but the sessions may be multi-hop and the direct connection nodes but the sessions may be multi-hop and the direct connection
discovery and liveliness detection for those connections are discovery and liveliness detection for those connections are
independent of the BGP protocol. How this is accomplished is outside independent of the BGP protocol. How this is accomplished is outside
the scope of this document. Consequently, there will be a single the scope of this document. Consequently, there will be a single
session even if there are multiple direct connections between BGP session even if there are multiple direct connections between BGP
speakers. For the purposes of BGP SPF, Link NLRI is advertised as speakers. For the purposes of BGP SPF, Link NLRI is advertised as
long as a BGP session has been established, the Link-State/SPF long as a BGP session has been established, the Link-State/SPF
address family capability has been exchanged [RFC4790] and the address family capability has been exchanged [RFC4790] and the
corresponding link is up and considered operational. corresponding link is considered is up and considered operational.
2.3. BGP Peering in Route-Reflector or Controller Topology 2.3. BGP Peering in Route-Reflector or Controller Topology
In this model, BGP speakers peer solely with one or more Route In this model, BGP speakers peer solely with one or more Route
Reflectors [RFC4456] or controllers. As in the previous model, Reflectors [RFC4456] or controllers. As in the previous model,
direct connection discovery and liveliness detection for those direct connection discovery and liveliness detection for those
connections are done outside the BGP protocol. More specifically, connections are done outside the BGP protocol. More specifically,
the Liveliness detection is done using BFD protocol described in the Liveliness detection is done using BFD protocol described in
[RFC5880]. For the purposes of BGP SPF, Link NLRI is advertised as [RFC5880]. For the purposes of BGP SPF, Link NLRI is advertised as
long as the corresponding link is up and considered operational. long as the corresponding link is up and considered operational.
3. BGP-LS Shortest Path Routing (SPF) SAFI 3. BGP-LS Shortest Path Routing (SPF) SAFI
In order to replace the Phase 1 and 2 decision functions of the In order to replace the Phase 1 and 2 decision functions of the
existing Decision Process with an SPF-based Decision Process and existing Decision Process with an SPF-based Decision Process and
streamline the Phase 3 decision functions in a backward compatible streamline the Phase 3 decision functions in a backward compatible
manner, this draft introduces a couple AFI/SAFIs for BGP LS SPF manner, this draft introduces the BGP-LS-SFP SAFI for BGP-LS SPF
operation. The BGP-LS-SPF (AF 16388 / SAFI TBD1) and BGP-LS-SPF-VPN operation. The BGP-LS-SPF (AF 16388 / SAFI TBD1) [RFC4790] is
(AFI 16388 / SAFI TBD2) [RFC4790] are allocated by IANA as specified allocated by IANA as specified in the Section 6. A BGP speaker using
in the Section 6. A BGP speaker wanting to run BGP LS SPF operation the BGP-LS SPF extensions described herein MUST exchange the AFI/SAFI
must exchange the AFI/SAFI using Multiprotocol Extensions Capabilty using Multiprotocol Extensions Capability Code [RFC4760] with other
Code, as defined in [RFC4760]. BGP speakers in the SPF routing domain.
4. Extensions to BGP-LS 4. Extensions to BGP-LS
[RFC7752] describes a mechanism by which link-state and TE [RFC7752] describes a mechanism by which link-state and TE
information can be collected from networks and shared with external information can be collected from networks and shared with external
components using BGP protocol. It contains two parts: definition of components using BGP protocol. It describes both the definition of
a new BGP NLRI that describes links, nodes, and prefixes comprising BGP-LS NLRI that describes links, nodes, and prefixes comprising IGP
IGP link-state information and definition of a new BGP path attribute link-state information and the definition of a BGP path attribute
(BGP-LS attribute) that carries link, node, and prefix properties and (BGP-LS attribute) that carries link, node, and prefix properties and
attributes, such as the link and prefix metric or auxiliary Router- attributes, such as the link and prefix metric or auxiliary Router-
IDs of nodes, etc. IDs of nodes, etc.
The BGP protocol will be used in the Protocol-ID field specified in The BGP protocol will be used in the Protocol-ID field specified in
table 1 of [I-D.ietf-idr-bgpls-segment-routing-epe]. The local and table 1 of [I-D.ietf-idr-bgpls-segment-routing-epe]. The local and
remote node descriptors for all NLRI will be the BGP Router-ID (TLV remote node descriptors for all NLRI will be the BGP Router-ID (TLV
516) and either the AS Number (TLV 512) [RFC7752] or the BGP 516) and either the AS Number (TLV 512) [RFC7752] or the BGP
Confederation Member (TLV 517) Confederation Member (TLV 517)
[I-D.ietf-idr-bgpls-segment-routing-epe]. However, if the BGP [I-D.ietf-idr-bgpls-segment-routing-epe]. However, if the BGP
Router-ID is known to be unique within the BGP Routing domain, it can Router-ID is known to be unique within the BGP Routing domain, it can
be used as the sole descriptor. be used as the sole descriptor.
4.1. Node NLRI Usage and Modifications 4.1. Node NLRI Usage and Modifications
The SPF capability is a new Node Attribute TLV that will be added to The SPF capability is a new Node Attribute TLV that will be added to
those defined in table 7 of [RFC7752]. The new attribute TLV will those defined in table 7 of [RFC7752]. The new attribute TLV will
only be applicable when BGP is specified in the Node NLRI Protocol ID only be applicable when BGP is specified in the Node NLRI Protocol ID
field. The TBD TLV type will be defined by IANA. The new Node field. The TBD TLV type will be defined by IANA. The new Node
Attribute TLV will contain a single octet SPF algorithm field: Attribute TLV will contain a single-octet SPF algorithm as defined in
[I-D.ietf-ospf-segment-routing-extensions].
0 1 2 3 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 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 | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPF Algorithm | | SPF Algorithm |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The SPF Algorithm may take the following values: The SPF Algorithm may take the following values:
1 - Normal SPF 0 - Normal Shortest Path First (SPF) algorithm based on link
2 - Strict SPF metric. This is the standard shortest path algorithm as
computed by the IGP protocol. Consistent with the deployed
practice for link-state protocols, Algorithm 0 permits any
node to overwrite the SPF path with a different path based on
its local policy.
1 - Strict Shortest Path First (SPF) algorithm based on link
metric. The algorithm is identical to Algorithm 0 but Algorithm
1 requires that all nodes along the path will honor the SPF
routing decision. Local policy at the node claiming support for
Algorithm 1 MUST NOT alter the SPF paths computed by Algorithm 1.
When computing the SPF for a given BGP routing domain, only BGP nodes When computing the SPF for a given BGP routing domain, only BGP nodes
advertising the SPF capability attribute will be included the advertising the SPF capability attribute will be included the
Shortest Path Tree (SPT). Shortest Path Tree (SPT).
4.2. Link NLRI Usage 4.2. Link NLRI Usage
The criteria for advertisement of Link NLRI are discussed in The criteria for advertisement of Link NLRI are discussed in
Section 2. Section 2.
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remote IPv4 (TLV 260) addresses will be used. For IPv6 links, the remote IPv4 (TLV 260) addresses will be used. For IPv6 links, the
local IPv6 (TLV 261) and remote IPv6 (TLV 262) addresses will be local IPv6 (TLV 261) and remote IPv6 (TLV 262) addresses will be
used. For unnumbered links, the link local/remote identifiers (TLV used. For unnumbered links, the link local/remote identifiers (TLV
258) will be used. For links supporting having both IPv4 and IPv6 258) will be used. For links supporting having both IPv4 and IPv6
addresses, both sets of descriptors may be included in the same Link addresses, both sets of descriptors may be included in the same Link
NLRI. The link identifiers are described in table 5 of [RFC7752]. NLRI. The link identifiers are described in table 5 of [RFC7752].
The link IGP metric attribute TLV (TLV 1095) as well as any others The link IGP metric attribute TLV (TLV 1095) as well as any others
required for non-SPF purposes SHOULD be advertised. Algorithms such required for non-SPF purposes SHOULD be advertised. Algorithms such
as setting the metric inversely to the link speed as done in the OSPF as setting the metric inversely to the link speed as done in the OSPF
MIB [RFC4750] may be supported. However, this is beyond the scope of MIB [RFC4750] MAY be supported. However, this is beyond the scope of
this document. this document.
4.3. Prefix NLRI Usage 4.3. Prefix NLRI Usage
Prefix NLRI is advertised with a local descriptor as described above Prefix NLRI is advertised with a local node descriptor as described
and the prefix and length used as the descriptors (TLV 265) as above and the prefix and length used as the descriptors (TLV 265) as
described in [RFC7752]. The prefix metric attribute TLV (TLV 1155) described in [RFC7752]. The prefix metric attribute TLV (TLV 1155)
as well as any others required for non-SPF purposes SHOULD be as well as any others required for non-SPF purposes SHOULD be
advertised. For loopback prefixes, the metric should be 0. For non- advertised. For loopback prefixes, the metric should be 0. For non-
loopback, the setting of the metric is beyond the scope of this loopback prefixes, the setting of the metric is a local matter and
document. beyond the scope of this document.
4.4. BGP-LS Attribute Sequence-Number TLV 4.4. BGP-LS Attribute Sequence-Number TLV
A new BGP-LS Attribute TLV to BGP-LS NLRI types is defined to assure A new BGP-LS Attribute TLV to BGP-LS NLRI types is defined to assure
the most recent version of a given NLRI is used in the SPF the most recent version of a given NLRI is used in the SPF
computation. The TBD TLV type will be defined by IANA. The new BGP- computation. The TBD TLV type will be defined by IANA. The new BGP-
LS Attribute TLV will contain an 8 octet sequence number. The usage LS Attribute TLV will contain an 8-octet sequence number. The usage
of the Sequence Number TLV is described in Section 5.1. of the Sequence Number TLV is described in Section 5.1.
0 1 2 3 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 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 | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (High-Order 32 Bits) | | Sequence Number (High-Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (Low-Order 32 Bits) | | Sequence Number (Low-Order 32 Bits) |
skipping to change at page 8, line 42 skipping to change at page 8, line 50
Sequence Number Sequence Number
The 64-bit strictly increasing sequence number is incremented for The 64-bit strictly increasing sequence number is incremented for
every version of BGP-LS NLRI originated. BGP speakers implementing every version of BGP-LS NLRI originated. BGP speakers implementing
this specification MUST use available mechanisms to preserve the this specification MUST use available mechanisms to preserve the
sequence number's strictly increasing property for the deployed life sequence number's strictly increasing property for the deployed life
of the BGP speaker (including cold restarts). One mechanism for of the BGP speaker (including cold restarts). One mechanism for
accomplishing this would be to use the high-order 32 bits of the accomplishing this would be to use the high-order 32 bits of the
sequence number as a wrap/boot count that is incremented anytime the sequence number as a wrap/boot count that is incremented anytime the
BGP Router router loses its sequence number state or the low-order 32 BGP router loses its sequence number state or the low-order 32 bits
bits wrap. wrap.
When incrementing the sequence number for each self-originated NLRI, When incrementing the sequence number for each self-originated NLRI,
the sequence number should be treated as an unsigned 64-bit value. the sequence number should be treated as an unsigned 64-bit value.
If the lower-order 32-bit value wraps, the higher-order 32-bit value If the lower-order 32-bit value wraps, the higher-order 32-bit value
should be incremented and saved in non-volatile storage. If by some should be incremented and saved in non-volatile storage. If by some
chance the BGP Speaker is deployed long enough that there is a chance the BGP Speaker is deployed long enough that there is a
possibility that the 64-bit sequence number may wrap or a BGP Speaker possibility that the 64-bit sequence number may wrap or a BGP Speaker
completely loses its sequence number state (e.g, the BGP speaker completely loses its sequence number state (e.g., the BGP speaker
hardware is replaced), the phase 1 decision function (see hardware is replaced or experiences a cold-start), the phase 1
Section 5.1) rules should insure convergance, albeit, not decision function (see Section 5.1) rules will insure convergence,
immediately. albeit, not immediately.
5. Decision Process with SPF Algorithm 5. Decision Process with SPF Algorithm
The Decision Process described in [RFC4271] takes place in three The Decision Process described in [RFC4271] takes place in three
distinct phases. The Phase 1 decision function of the Decision distinct phases. The Phase 1 decision function of the Decision
Process is responsible for calculating the degree of preference for Process is responsible for calculating the degree of preference for
each route received from a Speaker's peer. The Phase 2 decision each route received from a BGP speaker's peer. The Phase 2 decision
function is invoked on completion of the Phase 1 decision function function is invoked on completion of the Phase 1 decision function
and is responsible for choosing the best route out of all those and is responsible for choosing the best route out of all those
available for each distinct destination, and for installing each available for each distinct destination, and for installing each
chosen route into the Loc-RIB. The combination of the Phase 1 and 2 chosen route into the Loc-RIB. The combination of the Phase 1 and 2
decision functions is also known as a Path vector algorithm. decision functions is characterized as a Path Vector algorithm.
The SPF based Decision process replaces the BGP Bestpath Decision The SPF based Decision process replaces the BGP best-path Decision
process described in [RFC4271]. This process starts with selecting process described in [RFC4271]. This process starts with selecting
only those Node NLRI whose SPF capability TLV matches with the local only those Node NLRI whose SPF capability TLV matches with the local
BGP speaker's SPF capability TLV value. Since Link-State NLRI always BGP speaker's SPF capability TLV value. Since Link-State NLRI always
contains the local descriptor [RFC7752], it will only be originated contains the local descriptor [RFC7752], it will only be originated
by a single BGP speaker in the BGP routing domain. These selected by a single BGP speaker in the BGP routing domain. These selected
Node NLRI and their Link/Prefix NLRI are used to build a directed Node NLRI and their Link/Prefix NLRI are used to build a directed
graph during the SPF computation. The best paths for BGP prefixes graph during the SPF computation. The best paths for BGP prefixes
are installed as a result of the SPF process. are installed as a result of the SPF process.
When BGP-LS-SPF NLRI is received, all that is required is to When BGP-LS-SPF NLRI is received, all that is required is to
determine whether it is the best-path by examining the Node-ID and determine whether it is the best-path by examining the Node-ID and
sequence number as described in Section 5.1. If the received best- sequence number as described in Section 5.1. If the received best-
path NLRI had changed, it will be advertised to other BGP-LS-SPF path NLRI had changed, it will be advertised to other BGP-LS-SPF
peers. If the attributes have changed (other than the sequence peers. If the attributes have changed (other than the sequence
number), a BGP SPF calculation will be scheduled. However, a changed number), a BGP SPF calculation will be scheduled. However, a changed
best-path can be advertised to other peer immediately and propagation NLRI MAY be advertised to other peers almost immediately and
of changes can approach IGP convergence times with appropriately propagation of changes can approach IGP convergence times. To
tuned MinRouteAdvertisementIntervalTimer. accomplish this, the MinRouteAdvertisementIntervalTimer and
MinRouteAdvertisementIntervalTimer [RFC4271] are not applicable to
the BGP-LS-SPF SAFI.
The Phase 3 decision function of the Decision Process [RFC4271] is The Phase 3 decision function of the Decision Process [RFC4271] is
also simplified since under normal SPF operation, a BGP speaker would also simplified since under normal SPF operation, a BGP speaker would
advertise the NLRI selected for the SPF to all BGP peers with the advertise the NLRI selected for the SPF to all BGP peers with the
BGP-LS/BGP-SPF AFI/SAFI. Application of policy would not be BGP-LS/BGP-LS-SPF AFI/SAFI. Application of policy would not be
prevented however its usage to bestpath process would be limited as prevented however its usage to best-path process would be limited as
the SPF relies solely on link metrics. the SPF relies solely on link metrics.
5.1. Phase-1 BGP NLRI Selection 5.1. Phase-1 BGP NLRI Selection
The rules for NLRI selection are greatly simplified from [RFC4271]. The rules for NLRI selection are greatly simplified from [RFC4271].
1. If the NLRI is received from the BGP speaker originating the NLRI 1. If the NLRI is received from the BGP speaker originating the NLRI
(as determined by the comparing BGP Router ID in the NLRI Node (as determined by the comparing BGP Router ID in the NLRI Node
identifiers with the BGP speaker Router ID), then it is preferred identifiers with the BGP speaker Router ID), then it is preferred
over the same NLRI from non-originators. over the same NLRI from non-originators. This rule will assure
that stale NLRI is updated even if a BGP-LS router loses its
sequence number state due to a cold-start.
2. If the Sequence-Number TLV is present in the BGP-LS Attribute, 2. If the Sequence-Number TLV is present in the BGP-LS Attribute,
then the NLRI with the most recent, i.e., highest sequence number then the NLRI with the most recent, i.e., highest sequence number
is selected. BGP-LS NLRI with a Sequence-Number TLV will be is selected. BGP-LS NLRI with a Sequence-Number TLV will be
considered more recent than NLRI without a BGP-LS or a BGP-LS considered more recent than NLRI without a BGP-LS Attribute or a
Attribute that doesn't include the Sequence-Number TLV. BGP-LS Attribute that doesn't include the Sequence-Number TLV.
3. The final tie-breaker is the NLRI from the BGP Speaker with the 3. The final tie-breaker is the NLRI from the BGP Speaker with the
numerically largest BGP Router ID. numerically largest BGP Router ID.
The modified Decision Process with SPF algorithm uses the metric from The modified SPF Decision Process performs an SPF calculation rooted
Link and Prefix NLRI Attribute TLVs [RFC7752]. As a result, any at the BGP speaker using the metrics from Link and Prefix NLRI
attributes that would influence the Decision process defined in Attribute TLVs [RFC7752]. As a result, any attributes that would
[RFC4271] like ORIGIN, MULTI_EXIT_DISC, and LOCAL_PREF attributes are influence the Decision process defined in [RFC4271] like ORIGIN,
ignored by the SPF algorithm. Furthermore, the NEXT_HOP attribute MULTI_EXIT_DISC, and LOCAL_PREF attributes are ignored by the SPF
value is preserved but otherwise ignored during the SPF or best-path. algorithm. Furthermore, the NEXT_HOP attribute value is preserved
but otherwise ignored during the SPF or best-path.
5.2. Dual Stack Support 5.2. Dual Stack Support
The SPF based decision process operates on Node, Link, and Prefix The SPF-based decision process operates on Node, Link, and Prefix
NLRIs that support both IPv4 and IPv6 addresses. Whether to run a NLRIs that support both IPv4 and IPv6 addresses. Whether to run a
single SPF instance or multiple SPF instances for separate AFs is a single SPF instance or multiple SPF instances for separate AFs is a
matter of a local implementation. Normally, IPv4 next-hops are matter of a local implementation. Normally, IPv4 next-hops are
calculated for IPv4 prefixes and IPv6 next-hops are calculated for calculated for IPv4 prefixes and IPv6 next-hops are calculated for
IPv6 prefixes. However, an interesting use-case is deployment of IPv6 prefixes. However, an interesting use-case is deployment of
[RFC5549] where IPv6 link-local next-hops are calculated for both [RFC5549] where IPv6 next-hops are calculated for both IPv4 and IPv6
IPv4 and IPv6 prefixes. As stated in Section 1, support for Multiple prefixes. As stated in Section 1, support for Multiple Topology
Topology Routing (MTR) is an area for future study. Routing (MTR) is an area for future study.
5.3. NEXT_HOP Manipulation 5.3. NEXT_HOP Manipulation
A BGP speaker that supports SPF extensions MAY interact with peers A BGP speaker that supports SPF extensions MAY interact with peers
that don't support SPF extensions. If the BGP Link-State address that don't support SPF extensions. If the BGP-LS address family is
family is advertised to a peer not supporting the SPF extensions advertised to a peer not supporting the SPF extensions described
described herein, then the BGP speaker MUST conform to the NEXT_HOP herein, then the BGP speaker MUST conform to the NEXT_HOP rules
rules mentioned in [RFC4271] when announcing the Link-State address specified in [RFC4271] when announcing the Link-State address family
family routes to those peers. routes to those peers.
All BGP peers that support SPF extensions would locally compute the All BGP peers that support SPF extensions would locally compute the
NEXT_HOP values as result of the SPF process. As a result, the Loc-RIB next-hops as a result of the SPF process. Consequently, the
NEXT_HOP attribute is always ignored on receipt. However BGP NEXT_HOP attribute is always ignored on receipt. However, BGP
speakers should set the NEXT_HOP address according to the NEXT_HOP speakers SHOULD set the NEXT_HOP address according to the NEXT_HOP
attribute rules mentioned in [RFC4271]. attribute rules specified in [RFC4271].
5.4. IPv4/IPv6 Unicast Address Family Interaction 5.4. IPv4/IPv6 Unicast Address Family Interaction
While the BGP-LS SPF address family and the IPv4/IPv6 unicast address While the BGP-LS SPF address family and the IPv4/IPv6 unicast address
families install routes into the same device routing tables, they families install routes into the same device routing tables, they
will operate independently much the same as OSPF and IS-IS would will operate independently much the same as OSPF and IS-IS would
operate today (i.e., "Ships-in-the-Night" mode). There will be no operate today (i.e., "Ships-in-the-Night" mode). There will be no
implicit route redistribution between the BGP address families. implicit route redistribution between the BGP address families.
However, implementation specific redistribution mechanisms SHOULD be However, implementation specific redistribution mechanisms SHOULD be
made available with the restriction that redistribution of BGP-LS SPF made available with the restriction that redistribution of BGP-LS SPF
skipping to change at page 11, line 30 skipping to change at page 11, line 45
SPF tree and install the same set of routers, it is RECOMMENDED that SPF tree and install the same set of routers, it is RECOMMENDED that
BGP-LS SPF IPv4/IPv6 routes be given priority by default when BGP-LS SPF IPv4/IPv6 routes be given priority by default when
installed into their respective RIBs. In common implementations the installed into their respective RIBs. In common implementations the
prioritization is governed by route preference or administrative prioritization is governed by route preference or administrative
distance with lower being more preferred. distance with lower being more preferred.
5.5. NLRI Advertisement and Convergence 5.5. NLRI Advertisement and Convergence
A local failure will prevent a link from being used in the SPF A local failure will prevent a link from being used in the SPF
calculation due to the IGP bi-directional connectivity requirement. calculation due to the IGP bi-directional connectivity requirement.
Consequently, local link failues should always be given priority over Consequently, local link failures should always be given priority
updates (e.g., withdrawing all routes learned on a session) in order over updates (e.g., withdrawing all routes learned on a session) in
to ensure the highest priority progation and optimal convergence. order to ensure the highest priority propagation and optimal
convergence.
Delaying the withdrawal of non-local routes is an area for further Delaying the withdrawal of non-local routes is an area for further
study as more IGP-like mechanisms would be required to prevent usage study as more IGP-like mechanisms would be required to prevent usage
of stale NLRI. of stale NLRI.
5.6. Error Handling 5.6. Error Handling
When a BGP speaker receives a BGP Update containing a malformed SPF When a BGP speaker receives a BGP Update containing a malformed SPF
Capability TLV in the Node NLRI BGP-LS Attribute [RFC7752], it MUST Capability TLV in the Node NLRI BGP-LS Attribute [RFC7752], it MUST
ignore the received TLV and the Node NLRI and not pass it to other ignore the received TLV and the Node NLRI and not pass it to other
BGP peers as specified in [RFC7606]. When discarding a Node NLRI BGP peers as specified in [RFC7606]. When discarding a Node NLRI
with malformed TLV, a BGP speaker SHOULD log an error for further with malformed TLV, a BGP speaker SHOULD log an error for further
analysis. analysis.
6. IANA Considerations 6. IANA Considerations
This document defines a couple AFI/SAFIs for BGP LS SPF operation and This document defines an AFI/SAFI for BGP-LS SPF operation and
requests IANA to assign the BGP-LS-SPF AFI 16388 / SAFI TBD1 and the requests IANA to assign the BGP-LS/BGP-LS-SPF (AFI 16388 / SAFI TBD1)
BGP-LS-SPF-VPN AFI 16388 / SAFI TBD2 as described in [RFC4750]. as described in [RFC4750].
This document also defines two attribute TLV for BGP LS NLRI. We This document also defines two attribute TLV for BGP LS NLRI. We
request IANA to assign TLVs for the SPF capability and the Sequence request IANA to assign TLVs for the SPF capability and the Sequence
Number from the "BGP-LS Node Descriptor, Link Descriptor, Prefix Number from the "BGP-LS Node Descriptor, Link Descriptor, Prefix
Descriptor, and Attribute TLVs" Registry. Additionally, IANA is Descriptor, and Attribute TLVs" Registry.
requested to create a new registry for "BGP-LS SPF Capability
Algorithms" for the value of the algorithm both in the BGP-LS Node
Attribute TLV and the BGP SPF Capability. The initial assignments
are:
+-------------+-----------------------------------+
| Value(s) | Assignment Policy |
+-------------+-----------------------------------+
| 0 | Reserved (not to be assigned) |
| | |
| 1 | SPF |
| | |
| 2 | Strict SPF |
| | |
| 3-254 | Unassigned (IETF Review) |
| | |
| 255 | Reserved (not to be assigned) |
+-------------+-----------------------------------+
BGP-LS SPF Capability Algorithms
7. Security Considerations 7. Security Considerations
This extension to BGP does not change the underlying security issues This extension to BGP does not change the underlying security issues
inherent in the existing [RFC4724] and [RFC4271]. inherent in the existing [RFC4724] and [RFC4271].
7.1. Acknowledgements 7.1. Acknowledgements
The authors would like to thank .... for the review and comments. The authors would like to thank Sue Hares, Jorge Rabadan, and Boris
Hassanov for the review and comments.
7.2. Contributors 7.2. Contributors
In addition to the authors listed on the front page, the following In addition to the authors listed on the front page, the following
co-authors have contributed to the document. co-authors have contributed to the document.
Derek Yeung Derek Yeung
Arrcus, Inc. Arrcus, Inc.
derek@arrcus.com derek@arrcus.com
skipping to change at page 13, line 31 skipping to change at page 13, line 31
8. References 8. References
8.1. Normative References 8.1. Normative References
[I-D.ietf-idr-bgpls-segment-routing-epe] [I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Filsfils, C., Patel, K., Ray, S., and J. Previdi, S., Filsfils, C., Patel, K., Ray, S., and J.
Dong, "BGP-LS extensions for Segment Routing BGP Egress Dong, "BGP-LS extensions for Segment Routing BGP Egress
Peer Engineering", draft-ietf-idr-bgpls-segment-routing- Peer Engineering", draft-ietf-idr-bgpls-segment-routing-
epe-14 (work in progress), December 2017. epe-14 (work in progress), December 2017.
[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-25 (work in progress), April 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, <https://www.rfc- DOI 10.17487/RFC4271, January 2006, <https://www.rfc-
editor.org/info/rfc4271>. editor.org/info/rfc4271>.
skipping to change at page 14, line 10 skipping to change at page 14, line 16
S. Ray, "North-Bound Distribution of Link-State and S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752, Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016, <https://www.rfc- DOI 10.17487/RFC7752, March 2016, <https://www.rfc-
editor.org/info/rfc7752>. editor.org/info/rfc7752>.
[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
BGP for Routing in Large-Scale Data Centers", RFC 7938, BGP for Routing in Large-Scale Data Centers", RFC 7938,
DOI 10.17487/RFC7938, August 2016, <https://www.rfc- DOI 10.17487/RFC7938, August 2016, <https://www.rfc-
editor.org/info/rfc7938>. editor.org/info/rfc7938>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Information References 8.2. Information References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, <https://www.rfc- DOI 10.17487/RFC2328, April 1998, <https://www.rfc-
editor.org/info/rfc2328>. editor.org/info/rfc2328>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006, (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>. <https://www.rfc-editor.org/info/rfc4456>.
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