Internet DRAFT - draft-mishra-idr-v4-islands-v6-core-4pe
draft-mishra-idr-v4-islands-v6-core-4pe
BESS Working Group G. Mishra
Internet-Draft Verizon Inc.
Intended status: Standards Track J. Tantsura
Expires: 30 September 2023 Microsoft, Inc.
M. Mishra
Cisco Systems
S. Madhavi
Juniper Networks, Inc.
A. Simpson
Nokia
S. Chen
Huawei Technologies
29 March 2023
Connecting IPv4 Islands over IPv6 Core using IPv4 Provider Edge Routers
(4PE)
draft-mishra-idr-v4-islands-v6-core-4pe-04
Abstract
As operators migrate from an IPv4 core to an IPv6 core for global
table internet routing, the need arises to be able provide routing
connectivity for customers IPv4 only networks. This document
provides a solution called 4Provider Edge, "4PE" that connects IPv4
islands over an IPv6-Only Core Underlay Network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 30 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. 4PE Design Protocol Overview . . . . . . . . . . . . . . . . 5
4. 4PE Design procedures . . . . . . . . . . . . . . . . . . . . 6
5. 4PE SR-MPLS Support . . . . . . . . . . . . . . . . . . . . . 9
6. 4PE SRv6 Support . . . . . . . . . . . . . . . . . . . . . . 10
7. Crossing Multiple IPv6 Autonomous Systems . . . . . . . . . . 12
7.1. Inter-AS 4PE Overview . . . . . . . . . . . . . . . . . . 12
7.2. Advertisement of IPv4 prefixes using Inter-AS Style
Procedure A Procedures for 4PE . . . . . . . . . . . . . 13
7.3. Advertisement of labeled IPv4 prefixes Inter-AS Style
Procedure B and C . . . . . . . . . . . . . . . . . . . . 14
7.3.1. Advertisement of labeled IPv4 prefixes Inter-AS Style
Procedure B . . . . . . . . . . . . . . . . . . . . . 14
7.3.2. Multi-hop advertisement of labeled IPv4 prefixes
Inter-AS Style Procedure C . . . . . . . . . . . . . 15
8. IPv4 Islands over MPLS LDPv6 or SRv6 Core . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
This document explains the "4PE" design procedures and how to
interconnect IPv4 islands over a Multiprotocol Label Switching (MPLS)
LDPv6 enabled IPv6-Only core, Segment Routing (SR) enabled SR-MPLS
IPv6-Only core or SRv6 IPv6-Only core. The 4PE routers exchange the
IPv4 reachability information transparently over the core using the
Multiprotocol Border Gateway Protocol (MP-BGP) over IPv6. In doing
so, the BGP Next Hop field egress PE FEC (Forwarding Equivalency
Class) is used to convey the IPv6 address of the 4PE router learned
dynamically via IGP so that the dynamically established IPv6-signaled
MPLS Label Switched Paths (LSPs) or SRv6 Network Programming IPv6
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forwarding path instantiation and can be utilized without any
explicit tunnel configuration.
The 4PE design is required as an alternative to the use of standard
overlay tunneling technologies such as GRE/IP or any other tunneling
technologies which requries explicit tunnel termination at the tunnel
endpoints which creates added layer of complexity to the existing
MPLS or Segment routing underlay transport layer. The 4PE design
provides a solution for MPLS as well as Segment Routing environment,
where all tunnels are established dynamically using existing Service
Provider Network MPLS signalling or SRv6 Network Programming thereby
addressing environments where the effort to configure and maintain
explicitly configured tunnels is not acceptable.
Alternative designs exist in 6MAN and v6OPS Working groups related to
4to6 transition technologies referred to as "IPv4aas" IPv4 as-
a-service solutions [RFC9313] such as 464XLAT, Dual--Stack Lite, MAP-
E, MAP-T, however this document focuses on a BGP based solution "4PE'
to connecting IPv4 islands over an IPv6 Core network.
This design specifies operations of the 4PE approach for
interconnection of IPv4 islands over an MPLS LDP IPv6 core or Segment
Routing SR-MPLS IPv6 core or SRv6 core. The approach requires that
the Provider Edge (PE) routers Provider Edge - Customer Edge (PE-CE)
connections to Customer Edge (CE) IPv4 islands to be Dual Stack using
Multiprotocol BGP (MP-BGP) routers [RFC4760], while the core is a
[RFC5565] Softwire Mesh Framework single protocol Provider (P) Core
routers, are required only to support IPv6-Only dataplane to
transport IPv4 packets over an IPv6-Only Core supporting three core
technologies, MPLS LDPv6 [RFC5036] and Segment Routing, SR-MPLS
[RFC8660] and Segment Routing IPv6 (SRv6) SRv6 Network Programming
[RFC8986]. The approach uses MP-BGP over IPv6, relies on
identification of the 4PE routers by their IPv6 address, and uses an
underlay transport label switched IPv6-signaled MPLS, SR-MPLS LSP's,
underlay SRv6 SRv6-TE or SRv6 SRv6-BE Best Effort path instantiation
without any requirements for explicit tunnel configurations.
Throughout this document, the terminology of [RFC8200] and [RFC4364]
is used.
In this document an 'IPv4 island' is a network running native IPv4 as
per [RFC8200]. A typical example of an IPv4 island would be a
customer's IPv4 site connected via its IPv4 Customer Edge (CE) router
to one (or more) Dual Stack Provider Edge router(s) of a Service
Provider. These Dual Stacked or IPv4-Only Provider Edge routers
(4PE) are connected to an IPv6 MPLS core network.
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The interconnection method described in this document typically
applies to an Internet Service Provider (ISP) that has an MPLS LDP
IPv6 core, Segment Routing SR-MPLS IPv6 core or SRv6 core, that is
already offering IPv6 BGP/MPLS VPN services, that wants to continue
support IPv4 services to its customers. These 4PE PE Edge routers
provide connectivity to the Customer Edge (CE) IPv4 islands Edge
routers. They may also provide other services simultaneously (IPv6
connectivity, IPv6 L3VPN services, IPv6 L2VPN services, etc.). With
the 4PE approach, no tunnels need to be explicitly configured, and no
IPv6 headers need to be inserted in front of the IPv4 packets between
the customer and provider edge, PE-CE Demark.
The main use case for 4PE is where the operator needs to provide IPv4
island connectivity over an IPv6 Core network that uses MPLS, SR-
MPLS, SRv6 for the underlay transport where Layer 3 IP/VPN overlay
4VPE or VPN-IPv4 AFI/SAFI 1/128 [RFC4364] is not utilized such as for
internet service providers carrying the internet routing table in the
global table and not in a Layer 3 IP/VPN separate VRF instance or an
other similar use case.
The PE-CE interface between the edge router of the IPv4 island
Customer Edge (CE) router and the 4PE router is a native IPv4
interface which can be multiple physical or logical. Static routing
or a dynamic routing protocol Interior Gateway Protocol IGP, Open
Shortest Path First (OSPF) or Intermediate System Intermediate System
(ISIS) or Exterior Gatway Protocol such as BGP may run between the CE
router and the 4PE router for the distribution of IPv4 Network Layer
Reachability Information (NLRI).
The 4PE design described in this document can be used for customers
that require both IPv4 and IPv6 service as well as for customers that
require IPv4-Only connectivity thus providing global IPv4
reachability.
Deployment of the 4PE approach over an existing IPv6 MPLS or Segment
Routing core does not require an introduction of new mechanisms in
the core underlay transport. Configuration and operations of the 4PE
approach has similarities with the configuration and operations of an
IPv4 VPN service [RFC4364] or IPv6 VPN service [RFC4659] over an IPv6
MPLS or Segment Routing core because they all use MP-BGP to
distribute IPv4 Network Layer Reachability Information (NLRI) for
transport over an IPv6 Core.
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2. Requirements Language
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. 4PE Design Protocol Overview
Each IPv4 site is connected to at least one Provider Edge router that
is located on the border of the MPLS LDP IPv6 or Segment Routing SR-
MPLS IPv6 or SRv6 core. The PE router providing IPv4 connectivity to
the IPv4 Islands over an IPv6-Only Core is called a 4PE router. The
4PE router MUST be IPv4 and IPv6 dual stack . The 4PE router MUST be
configured with at least one IPv6 address on the IPv6 side and at
least one IPv4 address on the IPv4 side. In the MPLS LDP IPv6 and
SR-MPLS IPv6 Core scenario, the IPv6 address needs to be routable in
the IPv6 core. For the MPLS LDP IPv6 Core there MUST be an LDP IPv6
label binding, and for SR-MPLS an IPv6 Prefix / Node SID label
binding and for SRv6 SRH processing of SRv6 SID list [RFC8754] and
SRv6 Network Programming [RFC8986] SRv6 End.DX (Cross Connect to Next
Hop), End.DT (Table lookup) and SRv6 BGP Overlay Services [RFC9252]
The source side 4PE router receiving IPv4 packets from the local
Attachment Circuit (AC) PE-CE IPv4-Only or IPv4 and IPv6 Dual Stacked
interface Source IPv4 Site is called the Ingress 4PE router relative
to these IPv4 packets sent by the Source CE IPv4 Island. The
destination side 4PE router forwarding IPv4 packets to the local
Attachment Circuit (AC) PE-CE IPv4-Only or IPv4 and IPv6 Dual stacked
interface from the Source IPv4 Site sending location is called the
Egress 4PE router relative to these IPv4 packets received by the CE
IPv4 Island.
Every ingress 4PE router can signal an IPv6 MPLS LSP or instantiate
an SRv6 Best Effort (BE) or Segment Routing Traffic Engineering (SR-
TE) [RFC9256]. path to send to any egress 4PE router without
injecting any additional prefixes into the IPv6 core.
Interconnecting IPv4 islands over an IPv6 MPLS or Segment Routing
core takes place through the following steps:
1. Exchange IPv4 reachability information among 4PE Ingress and
Egress PE routers using MP- BGP [RFC2545]:
The 4PE routers MUST exchange the IPv4 prefixes over MP-BGP sessions
as per [RFC2545] running over IPv6. The MP-BGP Address Family
Identifier (AFI) used MUST be IPv4 (value 1). In doing so, the 4PE
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routers convey their IPv6 address as the BGP Next Hop for the
advertised IPv4 prefixes. The IPv6 address of the egress 4PE next
hop router MUST be encoded using [RFC8950] next hop encoding for the
BGP Next Hop field with a length of 16 or 32 bytes. The next hop
encoding [RFC8950] is constructed using MP-BGP for IPv6 [RFC2545] is
a 16 byte IPv6 Global Unicast Address followed by the 16 byte IPv6
Link Local Address if the Next Hop. In addition, the 4PE router MUST
bind a label to the IPv4 prefix as per [RFC8277]. The Subsequence
Address Family Identifier (SAFI) used in MP-BGP MUST be the "label"
SAFI (value 4) as defined in [RFC8277] called BGP Labeled Unicast
(BGP-LU). BGP Labeled Unicast hereinafter will be referred to as
BGP-LU. The Ingress and Egress PE Label Stack on the 4PE router
contains the Service label with Bottom of Stack "S" bit set and
contains the IPv4 NLRI prefixes "labeled" using BGP-LU, IPv4 Address
Family Identifier (AFI) IPv4 (value 1) Subsequent Address Family
Identifier (SAFI)(value 4). In some cases the there may be
additioanl AFI/SAFI being transported and thus the Service label may
have label space context that may be unique or common for each AFI/
SAFI that is being transported.
2. Transport IPv4 packets from the ingress 4PE router to the egress
4PE router over IPv6-signaled LSPs or SRv6 BE or SR-TE instantiated
path over an IPv6-only core:
The Ingress 4PE router MUST forward IPv4 NLRI as Labeled prefixes
using BGP-LU SAFI over the IPv6-signaled LSP towards the Egress 4PE
router identified by the IPv4 address advertised in the IPv6 next hop
encoding per [RFC8950].
The 4PE design is fully applicable to both full mesh BGP peering
between all Ingress and Egress PE's as well as when Route Reflectors
iBGP peering is used where the PEs are all Route Reflector Clients or
other use cases such as in a BGP only Data Center [RFC7938] where
Spine layer eBGP Route Servers are utilized as per BGP specification
[RFC4271].
4. 4PE Design procedures
In this design, using IPv6 Next hop encoding defined in [RFC8950]
allows a 4PE router that has to forward an IPv4 packets to
automatically determine the IPv6-signaled LSP to use for a particular
IPv4 destination by using the MP-BGP IPv4 NLRI.
The IPv6-signaled LSPs can be established using any existing
technique for label setup [RFC3031] using Label Distribution Protocol
(LDP) [RFC5036] or Resource Reservation Protocol (RSVP-TE) [RFC3209].
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To ensure interoperability among systems that implement the 4PE
design described in this document, all such systems MUST support
building the underlay tunneling using IPv6-signaled MPLS LSPs
established by LDP [RFC5036] or Resource Reservation Protocol (RSVP-
TE) [RFC3209].
When tunneling IPv4 packets over the IPv6 MPLS core, rather than
successively prepend an IPv6 header and then perform label imposition
based on the IPv6 header, the ingress 4PE Router MUST directly
perform label imposition of the IPv4 header without prepending any
IPv6 header. The (outer) label imposed MUST correspond to the IPv6-
signaled LSP starting on the ingress 4PE Router and ending on the
egress 4PE Router.
While this design concept could theoretically operate in some
situations using a single underlay label, one option is to use a a
second level of labels that are bound to the customer CE's IPv4
prefixes via MP-BGP advertisements in accordance with [RFC8277].
The reason for the use of a second level bottom of stack service
label, labeling the IPv4 prefixes is that it allows for Penultimate
Hop Popping (PHP) on the IPv6 Label Switch Router (LSR) Provider (P)
node, upstream of the egress 4PE router, having a 2 level label stack
even after te PHP transport label has been popped, the Bototm of
Stack (BOS) service label is now still present, so the PHP node still
transmits the labeled packets, instead of having to transmit
unlableled IPv4 packets and encapsulate them appropriately. If the
Core underlay network is a single protocol IPv6 core per RFC 5565
[RFC8277] Softwire Mesh framework then the IPv4 packet will be
dropped. The problem is stated in [RFC3032] that in the label stack
encoding when the topmost label is popped the remaining protocol type
cannot be identified and forwarded if of a different protocol type
thus is not allowed. For example over an IPv6 core, when the topmost
label is popped at the PHP node and if the protocol exposed is native
IPv4, the IPv4 protocol is not enabled on single protocol core
[RFC5565] Softwire Mesh framework, the packet will be dropped by the
receiving egress PE LSR.
Another critical reason for the second label is that an existing
IPv6-signaled LSP that is using "IPv6 Explicit NULL label" over the
last hop (e.g., because that LSP is already being used to transport
IPv6 traffic with the Pipe Diff-Serv Tunneling Model as defined in
[RFC3270]) could not be used to carry IPv4 with a single label since
the "IPv6 Explicit NULL label" cannot be used to carry native IPv4
traffic (see [RFC3032]), while it could be used to carry Labeled IPv4
traffic (see [RFC4182]).
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This is why it is recommended to use a 2 level label stack with the
4PE design.
The label bound by MP-BGP to the IPv4 prefix indicates to the egress
4PE Router that the packet is an IPv4 packet. This label advertised
by the egress 4PE Router with MP-BGP MAY be an arbitrary label value,
which identifies an IPv4 routing context or outgoing interface to
forward the packet, or could be the IPv4 Explicit Null Label Pipe
Diff-Serv Tunneling Model use case as defined in [RFC3270]). An
ingress 4PE Router MUST be able to accept any such advertised label.
BGP/MPLS VPN [RFC4798] defines 3 label allocation modes for Layer 3
VPN's per prefix where all prefixes are labeld, Per-CE label
allocation mode where all prefixes from a CE next hop are given the
same label and a Per-VRF label allocation mode where all prefixes
that belong to a VRF are given the same label. These options are
available for L3 VPN for scalability and are applicable to the 4PE
design. The two level label stack using a per prefix label
allcoation mode is what is used in [RFC4798] with a requirement to
label all the IPv6 prefixes using BGP-LU [RFC8277]. The 4PE design
provides the same operator flxeiblity as BGP/MPLS VPN [RFC4798], 2
level label stack option using Per-CE label allocation mode where the
next hop is label so all prefixes associated with CE get the same
label. The 4PE design provides the same operator flxeiblity as BGP/
MPLS VPN [RFC4798], 2 level label stack option using Per-VRF label
allocation mode where all prefixes within a VRF get the same is
label.
Every link in the IPv4 Internet must have an MTU of 576 octets or
larger per [RFC1122]. Therefore, on MPLS links that are used for
transport of IPv4, as per the 4PE approach, and that do not support
link-specific fragmentation and reassembly, the MTU must be
configured to at least 1280 octets plus the MPLS label stack
encapsulation overhead bytes.
Some IPv4 hosts might be sending packets larger than the MTU
available in the IPv6 MPLS core and rely on Path MTU discovery to
learn about those links. To simplify MTU discovery operations, one
option is for the network administrator to engineer the MTU on the
core facing interfaces of the ingress 4PE consistent with the core
MTU. ICMP ' Destination Unreachable' messages can then be sent back
by the ingress 4PE without the corresponding packets ever entering
the MPLS core. Otherwise, routers in the IPv6 MPLS network have the
option to generate an ICMP "Destination Unreachable" Fragmentation
Required Type 3 Code 4 message using mechanisms as described in
Section 2.3.2, "Tunneling Private Addresses through a Public
Backbone" of [RFC3032].
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Note that in the above case, should a core router with an outgoing
link with an MTU smaller than 1280 receive an encapsulated IPv4
packet larger than 576, then the mechanisms of [RFC3032] may result
in the "Unreachable" message never reaching the sender. This is
because, according to [RFC4443], the underlay LSR (LSP or RSVP-TE
tunnel) will build an ICMP "Unreachable " message filled with the
invoking packet up to 1280 bytes, and when forwarding downstream
towards the egress PE as per [RFC3032], the MTU of the outgoing link
will cause the packet to be dropped. This may cause significant
operational problems; the originator of the packets will notice that
his data is not getting through, without knowing why and where they
are discarded. This issue would only occur if the above
recommendation (to configure MTU on MPLS links of at least 1280
octets plus encapsulation overhead) is not adhered to (perhaps by
misconfiguration).
5. 4PE SR-MPLS Support
Segment Routing (SR) [RFC8402] leverages the source-routing paradigm
to steer packets from a source node through a controlled set of
instructions, called segments, by prepending the packet with an SR
header in the MPLS data plane SR-MPLS [RFC8660] through a label stack
or IPv6 data plane using an Segment Routing Header (SRH) header via
SRv6 [RFC8754] to construct an SR path. Segment Routing will be
referred to hereinafter as "SR". SR uses instructions called
segments which can be topological segments used for transport
underlay traffic steering or service instructions for overlay
services. SR's Source Routing Architecture provides a mechansim to
steer a flow onto a topological path, while maintaining per flow
state only on the ingress source nodes within the SR domain. SR-MPLS
reuses the Interior Gateway Protocol (IGP) control plane as well as
the MPLS forwarding plane functions as the SR segments are
instantiated as MPLS labels and the Segment Routing SR-MPLS Header is
instantiated as a stack of MPLS labels. SR-MPLS L2 VPN and L3 VPN
services can be steered using Traffic Engineered paths using SR-TE
Policy coloring for the path instantiation per [RFC9256] and
[I-D.ietf-idr-segment-routing-te-policy].
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The 4PE design suports the Segment Routing SR-MPLS architecture
[RFC8660], as SR-MPLS reuses the MPLS data plane with a new
forwarding context using topological SIDs. The 4PE underlay
signalling going from MPLS to SR-MPLS remains the same as the IPv6
LSP is still signalled as before from ingress PE to egress PE MPLS
data plane procedrues defined in [RFC3031]. The 4PE BGP overlay the
design for SR-MPLS is identical to MPLS where the Ingress and Egress
PE Label Stack on the 4PE router contains the Service label with
Bottom of Stack "S" bit set and contains the IPv4 NLRI prefixes
"labeled" using BGP-LU, IPv4 Address Family Identifier (AFI) IPv4
(value 1) Subsequent Address Family Identifier (SAFI)(value 4).
SR-MPLS can use Inter-AS options for 4PE procedures which is
identical to MPLS as well as can use SR-TE Policy and Binding SID for
candidate path per [RFC9256] and
[I-D.ietf-idr-segment-routing-te-policy].
6. 4PE SRv6 Support
Segment Routing (SR) [RFC3031] SRv6 leverages the source-routing
paradigm to steer packets from a source node through a controlled set
of instructions, called segments, by prepending the packet with a new
SR header over an IPv6 data plane called an IPv6 Routing Extension
Header type 4 called a Segment Routing Header (SRH) header with IPv6
SRH encoding [RFC8754] to construct an SR steered path. SRv6 Network
Programming framework provides the mechanism based on segment
endpoint behaviors to encode a sequence of instructions called
Segments into an IPv6 header. SRv6 defines a topological or service
segment as an IPv6 address with is called hereinafter a SID or
"Segment ID". Each SID is encoded into an SRH header per [RFC8754]on
the SR domain source node in the SR domain to steer a flow onto a
topological path. In SRv6 each SID is an IPv6 address with format
LOC:FUNC:ARG where the LOCATOR field "LOC" is the L most significant
bits of the SID, followd by F bits of FUNCTION field "FUNC" and A
bits of ARGUMENT "ARG". Each node in the SRv6 domain has a "LOC"
prefix assigned which is routable and it leads to the SRv6 node which
instantiates the SID by performing the endpoint processing on the
node. The SRv6 SID FUNCTION "FUNC" field is used to encode the BGP/
MPLS L3 VPN [RFC4364] or BGP EVPN Service labels [RFC7432] as defined
in SRv6 BGP Overlay Services [RFC9252]. Intermediate nodes within an
SRv6 domain process the topolocial SID at each segment endpoint
defined in the SRH header until the packet reaches the egress PE
where decapsulation happens similar to BGP/MPLS L3 VPN [RFC4364],
where the service labels encoded in the FUNC field can be
instantiated and processed for the corresponding Layer 2 VPN and
Layer 3 VPN service specific endpoint functions. SRv6 based BGP
services referes to Layer 2 VPN and Layer 3 VPN overlay services with
BGP as a control plane and SRv6 as a Data Plane to provide Best
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Effort (BE) which means that an SRH is not present and is reffered to
as SRv6-BE. SRv6 based BGP services referes to Layer 2 VPN and Layer
3 VPN overlay services with BGP as a control plane and SRv6 as a Data
Plane to provide Traffic Engineered (TE) which means that an SRH is
present is reffered to as SRv6-TE policy for SRH topological
instruction encoding for SR-TE Policy coloring for path steering
instantiation per [RFC9256] and
[I-D.ietf-idr-segment-routing-te-policy]. SRv6 Service SID and
refers to an SRv6 SID associated with one of the service-specific
endpoint behaviors on the advertising PE router such as END.DT
(Table Lookup in a VRF) or END.DX (Cross Connect to a Next Hop)
behaviors for Layer 3 VPN services defined in SRv6 Network
Programming [RFC8986] BGP Prefix SID Attribue is used to carry the
SRv6 SIDs and their associaed BGP Address Families and defines a SRv6
L3 Service TLV which encodes the SRv6 Service SID Information for
SRv6 based L3 Services. SRv6-BE providing "Best Effort" connectivity
where an SRH is not present, the egress PE signals the SRv6 Service
SID with the BGP overlay service route and encapsulates the payload
in an outer IPv6 header where the destination address is the SRv6
Service SID enclosed in SRv6 Service TLV(s) provided by the Egress PE
in which case the underlay need only support plan IPv6 forwarding.
SRv6-TE provides connectivity over a "Traffic Engineered" (TE) path
by encapsulating the payload packet in an outer IPv6 header with the
segment list of the SR policy related to the SLA along with SRv6
Service SID enclosed in SRv6 Service TLV(s) assoicated with route
using SRH segment list encoding [RFC8754] from ingress PE to egress
PE, the egress PE colors the overlay service route with a Color
Extended Community [I-D.ietf-idr-segment-routing-te-policy] to
instantiate the steering of flows with per flow state only maintained
on the SRv6 source node and all underlay nodes whos SRv6 SID are part
of the SRH Segment List MUST support the SRv6 Data Plane forwarding.
In the 4PE design over an SRv6 network using SRv6 Netowrk Programming
[RFC8986] forwarding plane would use endpoint behavior "Endpoint with
decapsulation and IPv4 cross-connect" behavior ("End.DX4" for short)
is a variant of the End.X behavior for Global Table IPv4 Routing over
SRv6 Core. The End.DX4 SID MUST be the last segment in an SR Policy,
and it is associated with one or more L3 IPv4 adjacencies and and
SRv6 BGP Overlay Services [RFC9252] where the next hop encoding
[RFC8950] is constructed using MP-BGP for IPv6 [RFC2545] is a 16 byte
IPv6 Global Unicast Address followed by the 16 byte IPv6 Link Local
Address if the Next Hop. In the 4PE design the SRv6 L3 Service SID
is encoded as part of the SRv6 L3 Service TLV for SRv6 Netowrk
Programming [RFC8986] endpoint behavior End.DX4 BGP Prefix SID
Attribute encoding of SRv6 Service SID, SRv6 L3 Service TLV encoding
[RFC9252] advertised by egress PEs which supports SRv6 based Layer 3
Services along with Service SID enclosed in SRv6 Layer 3 Service TLV,
Label field for an IPv4 prefix is encoded with 20-bit label value set
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as specified by BGP-LU [RFC8277] to the whole or portion of the
"FUNCTION" part of the SRv6 SID when the transposition encoding
scheme is used or otherwise set to NULL. The "FUNCTION" part of the
SRv6 SID now carries the overlay 4PE BGP-LU IPv4 Labeled prefix
identical to MPLS and SR-MPLS.
In the 4PE design over an SRv6 network using SRv6 Netowrk Programming
[RFC8986] forwarding plane would use endpoint behavior "Endpoint with
decapsulation and specific IPv4 table lookup" behavior ("End.DT4" for
short) is a variant of the End.T behavior for Global Table IPv4
Routing over SRv6 Core, The End.DT4 SID MUST be the last segment in
an SR Policy, and a SID instance is assocated with a IPv4 FIB
Table T. and SRv6 BGP Overlay Services [RFC9252] where the next hop
encoding [RFC8950] is constructed using MP-BGP for IPv6 [RFC2545] is
a 16 byte IPv6 Global Unicast Address followed by the 16 byte IPv6
Link Local Address if the Next Hop. In the 4PE design the SRv6 L3
Service SID is encoded as part of the SRv6 L3 Service TLV for SRv6
Netowrk Programming [RFC8986] endpoint behavior End.DT4 BGP Prefix
SID Attribute encoding of SRv6 Service SID, SRv6 L3 Service TLV
encoding [RFC9252] advertised by egress PEs which supports SRv6 based
Layer 3 Services along with Service SID enclosed in SRv6 Layer 3
Service TLV, Label field for an IPv4 prefix is encoded with 20-bit
label value set as specified by BGP-LU [RFC8277] to the whole or
portion of the "FUNCTION" part of the SRv6 SID when the transposition
encoding scheme is used or otherwise set to NULL. The "FUNCTION"
part of the SRv6 SID now carries the overlay 4PE BGP-LU IPv4 Labeled
prefix identical to MPLS and SR-MPLS.
SRv6 can use Inter-AS options for 4PE procedures which is equivalent
to MPLS using SRv6 Service SID enocded in BGP Prefix SID Attribute as
well as can use SR-TE Policy and Binding SID for candidate path per
[RFC9256] and [I-D.ietf-idr-segment-routing-te-policy].
7. Crossing Multiple IPv6 Autonomous Systems
7.1. Inter-AS 4PE Overview
This section discusses the use case where two IPv4 islands are
connected to different Core Autonomous Systems (ASes)and utilizes 4
PE to connect the two Core ASes together. The Inter-AS connectivity
is established by connecting the PE from one AS to the PE of another
AS, whereby the PE providing global table routing reachability
between ASes, as a 4PE router, is acting as an Autonomous System
Boundary Router (ASBR) to provide the Inter-AS ASBR to ASBR, PE to PE
connectivity between ASN's. In the 4PE design the Inter-AS link
extends the underlay transport LSP so it is now extended between the
ASes. Bottom of Stack S bit is set and using BGP-LU IPv4 BGP Labeled
Unicast all the IPv4 prefixes can now be advertised between the ASes.
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Like in the case of multi-AS backbone operations for IPv6 VPNs
described in Section 10 of [RFC4364], there are three inter-as design
options and a fourth option defined in [I-D.mapathak-interas-ab] that
are described below.
7.2. Advertisement of IPv4 prefixes using Inter-AS Style Procedure A
Procedures for 4PE
This 4PE Inter-AS extension involves the advertisement of IPv4
prefixes (non-Labeled) using Inter-AS Style procedure (a).
This design is the equivalent for exchange of IPv4 prefixes to Inter-
AS Style procedure (a) Back to Back CE (no-labeled) Inter-AS path
where each PE acts like a CE (No MPLS) as described in Section 10 of
[RFC4364] for the exchange of VPN-IPv4 prefixes. In the Inter-AS
Style Procedure (a) the Control plane carrying the (non-labeled)
prefixes is together per VRF subinterfaces with the Data Plane
forwarding over the Inter-AS ASBR to ASBR link.
In this design, the Source 4PE routers within the Source AS use IBGP
MP-BGP [RFC4760] carrying IPv4 NLRI over an IPv6 Next Hop using IPv6
Next hop encoding [RFC8950] and BGP-LU [RFC8277] to advertise labeled
IPv4 prefixes to a Route Reflector to which it is a client, which
then advertises the labeled IPv4 prefixes to an Autonomous System
Border Router (ASBR) 4PE router which is also a client of the route
reflector, connecting eBGP to another Autonomous System Border Router
(ASBR) 4PE router. The ASBR then uses eBGP to advertise the (non-
labeled) IPv4 prefixes to an ASBR in another AS, which in turn
advertises the IPv4 prefixes to a route reflector within that AS of
which it is a client which then advertises the IPv4 prefixes to all
the 4PE routers in that directly connected AS or as described earlier
in this specification to another ASBR, which in turn repeats the
Inter-AS Procedure (a) herinafter in a case where ASN's are linked
togetther with multiple 4PE AS hops.
There may be one, or multiple, ASBR interconnection(s) across any two
ASes. IPv4 MUST to be activated on the Inter-AS ASBR to ASBR (non-
labeled) links and each ASBR 4PE router MUST have at least one IPv4
address on the interface connected to the Inter-AS ASBR to ASBR, PE
to PE link.
No inter-AS LSPs are used are used in this Inter-AS Procedure (a) as
described in Section 10 of [RFC4364]. There is effectively a
separate mesh of LSPs across the 4PE routers within each AS for which
the (non-labeled) IPv4 prefixes are advertised within the AS as BGP-
LU IPv4 labled prefixes carried in the IPv6 signaled transport LSP
mesh.
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In this design, the ASBR exchanging IPv4 prefixes MUST peer over
IPv4. The exchange of IPv4 prefixes MUST be carried out as per
[RFC4760].
7.3. Advertisement of labeled IPv4 prefixes Inter-AS Style Procedure B
and C
7.3.1. Advertisement of labeled IPv4 prefixes Inter-AS Style Procedure
B
This 4PE Inter-AS extension involves the advertisement of labeled
IPv4 prefixes over a segmented LSP using Inter-AS Style procedure
(b). In this 4PE extension of Inter-AS Style procedure (b) the 4PE
IPv4 BGP-LU labeled Unicast RIB is maintained on the ASBR.
This design is the equivalent for exchange of IPv4 prefixes to Inter-
AS procedure (b) described in Section 10 of [RFC4364] for the
exchange of VPN-IPv4 prefixes. In the Inter-AS Style Procedure (b)
the Control plane carrying the Service label prefixes is together in
the label stack with the Data Plane forwarding over the Inter-AS ASBR
to ASBR link.
In this design, the Source 4PE routers within the Source AS use IBGP
MP-BGP [RFC4760] carrying IPv4 NLRI over an IPv6 Next Hop using IPv6
Next hop encoding [RFC8950] and BGP-LU [RFC8277] to advertise labeled
IPv4 prefixes to a Route Reflector to which it is a client, which
then advertises the labeled IPv4 prefixes to an Autonomous System
Border Router (ASBR) 4PE router which is also a client of the route
reflector, connecting eBGP to another Autonomous System Border Router
(ASBR) 4PE router. The ASBR then uses eBGP to advertise the labeled
IPv4 prefixes to an ASBR in another AS, which in turn advertises the
IPv4 prefixes to a route reflector within that AS of which it is a
client which then advertises the IPv4 prefixes to all the 4PE routers
in that directly connected AS or as described earlier in this
specification to another ASBR, which in turn repeats the Inter-AS
Procedure (a) herinafter in a case where ASN's are linked togetther
with multiple 4PE AS hops.
There may be one, or multiple, ASBR interconnection(s) across any two
ASes. The label stack on the ASBR to ASBR, PE to PE link is 2 labels
deep, with the IPv6 tompost transport label IPv6 signaled LSP using
BGP-LU IPv6 Labeled Unicast, IPv6 Address Family Identifier (AFI)
IPv4 (value 2) Subsequent Address Family Identifier (SAFI)(value 4)
and Bottom of Stack BGP-LU IPv4 labeled Unicast Service label, IPv4
Address Family Identifier (AFI) IPv4 (value 1) Subsequent Address
Family Identifier (SAFI)(value 4) Thus IPv4 is not required to be
activated on the Inter-AS ASBR to ASBR PE to PE links as IPv4 is
tunnled through the IPv6 signaled LSP.
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This 4PE Inter-AS procedure (b) described in Section 10 of [RFC4364]
requires that there be label switched paths established across ASes.
Hence the corresponding considerations described for procedure (b) in
Section 10 of [RFC4364] apply equally to this design regarding trust
relationship between Service Providers in extending the Inter-AS LSP
between ASBR's.
7.3.2. Multi-hop advertisement of labeled IPv4 prefixes Inter-AS Style
Procedure C
This 4PE Inter-AS extension involves the Route Reflector to Route
Reflector Control Plane Multi-hop eBGP advertisement of labeled IPv4
Unicast prefixes between source and destination ASes, with Inter-AS
link transport underlay IPv6 signaled LSP eBGP advertisement of
labeled Unicast IPv4 prefixes from AS to neighboring AS. In this 4PE
extension of Inter-AS Style procedure (c), the 4PE IPv4 BGP-LU
labeled Unicast RIB is not maintained on the ASBR.
This design is the equivalent for exchange of IPv4 prefixes to Inter-
AS procedure (c) described in Section 10 of [RFC4364] for exchange of
VPN-IPv4 prefixes. In the Inter-AS Style Procedure (c) the Control
plane carrying the Service label prefixes eBGP Multihop, Route
Reflector to Route Reflector is separated from the data plane
forwarding over the Inter-AS ASBR to ASBR link which caries the
underlay PE loopbacks advertised using BGP-LU between the Source and
Destination AS over the Inter-AS ASBR-ASBR link. The Core AS
underlay /128 PE loopbacks must be advertised in IPv6 Address Family
Identifier (AFI) IPv4 (value 2) Subsequent Address Family Identifier
(SAFI)(value 4).
In this design, the Source 4PE routers within the Source AS use IBGP
MP-BGP [RFC4760] carrying IPv4 NLRI over an IPv6 Next Hop using IPv6
Next hop encoding [RFC8950] and BGP-LU [RFC8277] to advertise the
control plane labeled IPv4 prefixes to a Route Reflector to which it
is a client, which then advertises the labeled IPv4 Unicast prefixes
over an eBGP Multihop Inter-AS peering to the route reflector in the
Destination AS. The ASBR in the Source AS over the Inter-AS ASBR to
ASBR link then uses eBGP to advertise the core underlay Labeled
Unicast IPv6 PE loopabcks prefixes in the underlay to an ASBR in
Destination AS, which in turn advertises the IPv6 PE loopabcks
prefixes to a route reflector within the Destination AS of which it
is a client which then advertises the PE loopabcks IPv6 prefixes to
all the PE routers within the AS to establish an end to end LSP from
ingress PE in the Source AS to egress PE in the Destination AS.
IPv4 need not be activated on the Inter-AS ASBR to ASBR, PE to PE
links.
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The considerations described for procedure (c) in Section 10 of
[RFC4364] with respect to possible use of multi-hop eBGP connections
via route-reflectors in different ASes, as well as with respect to
the use of a third label in case the IPv6 /128 prefixes for the PE
routers are NOT made known to the P routers, apply equally to this
design for IPv4 underlay transport.
There may be one, or multiple, ASBR interconnection(s) across any two
ASes. The label stack on the ASBR to ASBR, PE to PE link is 2 labels
deep, with the IPv6 tompost transport label IPv6 signaled LSP using
BGP-LU IPv6 Labeled Unicast, IPv6 Address Family Identifier (AFI)
IPv4 (value 2) Subsequent Address Family Identifier (SAFI)(value 4)
and the route reflector to route reflector Multihop eBGP Peering
next-hop-unchanged forwarding plane from ingress PE to egress PE
loopback with unchanged next-hop is forwarded over the Inter-AS ASBR
to ASBR PE-PE link, Bottom of Stack BGP-LU IPv4 labeled Unicast
Service label, IPv4 Address Family Identifier (AFI) IPv4 (value 1)
Subsequent Address Family Identifier (SAFI)(value 4) Thus IPv4 is not
required to be activated on the Inter-AS ASBR to ASBR PE to PE links
as IPv4 is tunnled through the IPv6 signaled LSP.
This 4PE design for procedure (c) in Section 10 of [RFC4364] requires
that there be IPv6 label switched paths established across the ASes
leading from a packet's ingress 4PE router to its egress 4PE router.
Hence the considerations described for procedure (c) in Section 10 of
[RFC4364], with respect to LSPs spanning multiple ASes, apply equally
to this design for IPv4.
Note that the 4PE Inter-AS extension for procedure (c) in Section 10
of [RFC4364] that the exchange of IPv4 prefixes control plane
function can only start after BGP has created IPv6 end to end LSP has
established between the ASes.
8. IPv4 Islands over MPLS LDPv6 or SRv6 Core
The new MP-BGP extensions defined in [RFC8950] is used to support
IPV4 islands over an IPv6 MPLS LDPv6 or SRv6 backbone. In this
scenario the PE routers would use BGP Labeled unicast address family
(BGP-LU) to advertise BGP with label binding and receive Labeled IPv4
NLRI in the MP_REACH_NLRI along with an IPv6 Next Hop from the Route
Reflector (RR).
MP-BGP Reach Pseudo code:
If ((Update AFI == IPv4)
and (Length of next hop == 16 Bytes || 32 Bytes))
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{
This is an IPv4 route, but
with an IPv6 next hop;
}
The MP_REACH_NLRI is encoded with:
* AFI = 1
* SAFI = 1
* Length of Next Hop Network Address = 16 (or 32)
* Network Address of Next Hop = IPv6 address of Next Hop whose RD is
set to zero
* NLRI = IPv4-VPN prefixes
During BGP Capability Advertisement, the PE routers would include the
following fields in the Capabilities Optional Parameter:
* Capability Code set to "Extended Next Hop Encoding"
* Capability Value containing <NLRI AFI=1, NLRI SAFI=1, Nexthop
AFI=2>
9. IANA Considerations
There are not any IANA considerations.
10. Security Considerations
No new extensions are defined in this document. As such, no new
security issues are raised beyond those that already exist in BGP-4
and use of MP-BGP for IPv6.
The security features of BGP and corresponding security policy
defined in the ISP domain are applicable.
For the inter-AS distribution of IPv6 prefixes according to case (a)
of Section 4 of this document, no new security issues are raised
beyond those that already exist in the use of eBGP for IPv6
[RFC2545].
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11. Acknowledgments
Many thanks to Ketan Talaulikar, Robert Raszuk, Igor Malyushkin,
Linda Dunbar, Huaimo Chen, Dikshit Saumya for your thoughtful reviews
and comments.
12. References
12.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Jain, D., and S. Lin, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
ietf-idr-segment-routing-te-policy-20, 27 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-20>.
[I-D.mapathak-interas-ab]
Pathak, M., Patel, K., and A. Sreekantiah, "Inter-AS
Option D for BGP/MPLS IP VPN", Work in Progress, Internet-
Draft, draft-mapathak-interas-ab-02, 28 May 2015,
<https://datatracker.ietf.org/doc/html/draft-mapathak-
interas-ab-02>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/info/rfc1812>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
DOI 10.17487/RFC2545, March 1999,
<https://www.rfc-editor.org/info/rfc2545>.
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[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A., and
B. Thomas, "LDP Specification", RFC 3036,
DOI 10.17487/RFC3036, January 2001,
<https://www.rfc-editor.org/info/rfc3036>.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001,
<https://www.rfc-editor.org/info/rfc3107>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, DOI 10.17487/RFC3270, May 2002,
<https://www.rfc-editor.org/info/rfc3270>.
[RFC4029] Lind, M., Ksinant, V., Park, S., Baudot, A., and P.
Savola, "Scenarios and Analysis for Introducing IPv6 into
ISP Networks", RFC 4029, DOI 10.17487/RFC4029, March 2005,
<https://www.rfc-editor.org/info/rfc4029>.
[RFC4182] Rosen, E., "Removing a Restriction on the use of MPLS
Explicit NULL", RFC 4182, DOI 10.17487/RFC4182, September
2005, <https://www.rfc-editor.org/info/rfc4182>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
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[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <https://www.rfc-editor.org/info/rfc5036>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
BGP for Routing in Large-Scale Data Centers", RFC 7938,
DOI 10.17487/RFC7938, August 2016,
<https://www.rfc-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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
<https://www.rfc-editor.org/info/rfc8277>.
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[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8950] Litkowski, S., Agrawal, S., Ananthamurthy, K., and K.
Patel, "Advertising IPv4 Network Layer Reachability
Information (NLRI) with an IPv6 Next Hop", RFC 8950,
DOI 10.17487/RFC8950, November 2020,
<https://www.rfc-editor.org/info/rfc8950>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[RFC9313] Lencse, G., Palet Martinez, J., Howard, L., Patterson, R.,
and I. Farrer, "Pros and Cons of IPv6 Transition
Technologies for IPv4-as-a-Service (IPv4aaS)", RFC 9313,
DOI 10.17487/RFC9313, October 2022,
<https://www.rfc-editor.org/info/rfc9313>.
12.2. Informative References
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[I-D.ietf-idr-dynamic-cap]
Chen, E. and S. R. Sangli, "Dynamic Capability for BGP-4",
Work in Progress, Internet-Draft, draft-ietf-idr-dynamic-
cap-16, 21 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
dynamic-cap-16>.
[RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
"BGP-MPLS IP Virtual Private Network (VPN) Extension for
IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
<https://www.rfc-editor.org/info/rfc4659>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC4798] De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS Using IPv6
Provider Edge Routers (6PE)", RFC 4798,
DOI 10.17487/RFC4798, February 2007,
<https://www.rfc-editor.org/info/rfc4798>.
[RFC4925] Li, X., Ed., Dawkins, S., Ed., Ward, D., Ed., and A.
Durand, Ed., "Softwire Problem Statement", RFC 4925,
DOI 10.17487/RFC4925, July 2007,
<https://www.rfc-editor.org/info/rfc4925>.
[RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
Layer Reachability Information with an IPv6 Next Hop",
RFC 5549, DOI 10.17487/RFC5549, May 2009,
<https://www.rfc-editor.org/info/rfc5549>.
[RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
Framework", RFC 5565, DOI 10.17487/RFC5565, June 2009,
<https://www.rfc-editor.org/info/rfc5565>.
[RFC6074] Rosen, E., Davie, B., Radoaca, V., and W. Luo,
"Provisioning, Auto-Discovery, and Signaling in Layer 2
Virtual Private Networks (L2VPNs)", RFC 6074,
DOI 10.17487/RFC6074, January 2011,
<https://www.rfc-editor.org/info/rfc6074>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
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[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Authors' Addresses
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Jeff Tantsura
Microsoft, Inc.
Email: jefftant.ietf@gmail.com
Mankamana Mishra
Cisco Systems
821 Alder Drive,
MILPITAS
Email: mankamis@cisco.com
Sudha Madhavi
Juniper Networks, Inc.
Email: smadhavi@juniper.net
Adam Simpson
Nokia
Email: adam.1.simpson@nokia.com
Shuanglong Chen
Huawei Technologies
Email: chenshuanglong@huawei.com
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