Connecting IPv4 Islands over IPv6 Core using IPv4 Provider Edge Routers (4PE)
draft-mishra-idr-v4-islands-v6-core-4pe-08
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Gyan Mishra , Jeff Tantsura , Mankamana Prasad Mishra , Sudha Madhavi , Adam Simpson , Shuanglong Chen | ||
| Last updated | 2024-11-02 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-mishra-idr-v4-islands-v6-core-4pe-08
BESS Working Group G. Mishra
Internet-Draft Verizon Inc.
Intended status: Informational J. Tantsura
Expires: 6 May 2025 Microsoft, Inc.
M. Mishra
Cisco Systems
S. Madhavi
Juniper Networks, Inc.
A. Simpson
Nokia
S. Chen
Huawei Technologies
2 November 2024
Connecting IPv4 Islands over IPv6 Core using IPv4 Provider Edge Routers
(4PE)
draft-mishra-idr-v4-islands-v6-core-4pe-08
Abstract
As operators migrate from an IPv4 core to an IPv6 core for global
table routing over the internet, 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 network.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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."
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This Internet-Draft will expire on 6 May 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. 4PE Design Protocol Overview . . . . . . . . . . . . . . . . 4
4. 4PE Design procedures . . . . . . . . . . . . . . . . . . . . 5
5. 4PE SR-MPLS Support . . . . . . . . . . . . . . . . . . . . . 8
6. 4PE SRv6 Support . . . . . . . . . . . . . . . . . . . . . . 8
7. 4PE Deployment Options . . . . . . . . . . . . . . . . . . . 8
7.1. Arbitrary topmost with all customer prefixes labeled . . 9
7.2. Arbitrary topmost with PE to PE LSP . . . . . . . . . . . 9
7.3. Arbitrary topmost with per CE label table . . . . . . . . 10
7.4. Explicit Null topmost with all customer prefixes
labeled . . . . . . . . . . . . . . . . . . . . . . . . 10
7.5. Explicit Null topmost with PE to PE LSP . . . . . . . . . 11
7.6. Explicit Null topmost with per CE label table . . . . . . 11
7.7. Implicit Null with all customer prefixes labeled . . . . 12
7.8. Implicit Null with PE to PE LSP . . . . . . . . . . . . . 12
7.9. Implicit Null with per CE label table . . . . . . . . . . 13
7.10. Arbitrary topmost with customer prefixes unlabeled . . . 13
7.11. Explicit Null topmost with customer prefixes unlabeled . 13
8. Crossing Multiple IPv6 Autonomous Systems . . . . . . . . . . 14
8.1. Inter-AS 4PE Overview . . . . . . . . . . . . . . . . . . 14
8.2. Advertisement of IPv4 prefixes Inter-AS Procedure A . . . 14
8.3. Advertisement of labeled IPv4 prefixes Inter-AS Procedure
B/C . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.3.1. Advertisement of labeled IPv4 prefixes Inter-AS
Procedure B . . . . . . . . . . . . . . . . . . . . . 15
8.3.2. Advertisement of labeled IPv4 prefixes Inter-AS
Procedure C . . . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
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11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
The problem being solved here for operators is how to connect IPv4
Islands over and IPv6 core without using traditional explicit complex
tunneling technologies or IPv6 transition technology tunneling
mechanisms which can be overly complicated.
"6PE" [RFC4798] is the specification for connecting IPv6 Islands over
IPv4 MPLS Core using IPv6 Provider Edge Routers (6PE). This document
explains the "4PE" design procedures and how to interconnect IPv4
islands over a IPv6-Only network. The 4PE routers exchange the IPv4
reachability information transparently over the core using the
Multiprotocol Border Gateway Protocol (MP-BGP) over IPv6. Each
ingress and egress PE (4PE) router builds an IPv6-signaled path
without any explicit tunnel configuration.
The 4PE design is an alternative to the use of standard overlay
tunneling technologies such as GRE/IP or any other tunneling
technologies which requries explicit tunneling. The 4PE design
provides a solution where all tunnels are established dynamically
using existing technologies.
4PE design specifies operations of the 4PE approach for
interconnection of IPv4 islands over an IPv6-Only network. 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 IPv6-Only network. The approach uses MP-BGP over IPv6
and relies on the identification of the 4PE routers by their IPv6
address without any requirements for complex explicit tunnel
configurations.
In this document an 'IPv4 island' is a network running native IPv4 as
per [RFC1812]. 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.
The interconnection method described in this document typically
applies to an operator that may or many not already be offering IPv6
BGP/MPLS VPN services for private MPLS, that wants to continue
support IPv4 services to its internet customers over the global
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routing table. The "4PE" PE Edge routers provide connectivity to the
disparate Customer Edge (CE) IPv4 islands Edge routers across an
IPv6-Only network. 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. Providing the IPv4 connectivity to customers over an IPv6
core network is a challenge and complicated without using MP-BGP as
described in this document.
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.
Configuration and operations of the 4PE overlay approach has
similarities to IPv4 VPN overlay service [RFC4364] or IPv6 VPN
overlay service [RFC4659] to distribute IPv4 Network Layer
Reachability Information (NLRI) for transport over an IPv6-Only
network.
2. Terminology
Terminolgoy used in defining the 4PE specification.
IPv6-Only Network: MPLS, SR-MPLS SRv6
3. 4PE Design Protocol Overview
Each IPv4 site is connected to at least one Provider Edge router
connected to the IPv6-Only network. The PE router providing IPv4
connectivity to the IPv4 Islands over an IPv6-Only network 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 Core side interface and at least one IPv4 address on the IPv4
Customer side PE-CE interface. The 4PE IPv6 address Loopback0 MUST
to be routable within the IPv6 core.
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.
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Every ingress 4PE router can signal a path to send to any egress 4PE
router without injecting any additional prefixes into the IPv6 core
other then the IPv6 signaled next hop Loopback0 used to identify the
Ingress and Egress 4PE router.
Interconnecting IPv4 islands 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 exchange IPv4 prefixes over MP-BGP sessions as per
[RFC2545] running over IPv6, MP-BGP Address Family Identifier (AFI)
IPv4=1. In doing so, the 4PE routers convey their IPv6 address FEC
label binding as the BGP Next Hop for the advertised IPv4 prefixes.
The IPv6 address of the egress 4PE next hop router is 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 is on a common subnet with peer. The ingress and egress 4PE
router has the option to bind a label to the IPv4 prefix as per
[RFC8277] using BGP Labeled Unicast.
2. Transport IPv4 packets from the ingress 4PE router to the egress
4PE router:
The Ingress 4PE router MAY 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.
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 path to use for a
particular IPv4 destination by using the MP-BGP IPv4 NLRI.
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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 has the option to
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 can operate in some situations using a
single underlay topmost transport 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 labeling the IPv4 prefixes is as follows: 1. Allows
for Penultimate Hop Popping (PHP) on the IPv6 Label Switch Router
(LSR), upstream of the egress 4PE router. 2. After the topmost
label has been popped, the Bototm of Stack (BOS) service label is now
still present. 3. PHP node still transmits the labeled packets,
instead of having to transmit unlableled IPv4 packets and now can
encapsulate them appropriately so they are not dropped.
Another reason for second level bottom of stack label is for the
existing IPv6-signaled LSP. This LSP is using "IPv6 Explicit NULL
label" over the last hop. This is becauase the LSP is already being
used to transport IPv6 traffic with the Pipe Diff-Serv Tunneling
Model as defined in [RFC3270]). Thus the LSP 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 [RFC3032]. While it
could be used to carry Labeled IPv4 traffic [RFC4182]. [RFC3032]
section 2.2 states that the LSR that pops the last label off the
label stack must be able to identify the packets network layer
protocol in this case IPv4. However, the label stack does not
contain any field that explicitly carries the network layer protocol.
Thus the network layer protocol must be inferrable from the value of
the label which is popped from the bottom of the label stack along
with subsequent headers. It is up to the network designer as to
labeling the IPv4 prefixes or not based on the use case and desired
and requirements. There maybe cases where it is not desirable to
label the IPv4 prefixes and instead use a per CE label table LSP to
carry the per CE unlabled IPv4 prefixes in a separate IPv4 routing
context.
The label bound by MP-BGP to the IPv4 prefix indicates to the egress
4PE Router that the packet is an IPv4 packet. The label advertised
by the egress 4PE Router with MP-BGP MAY be an explicit Null label
Pipe mode Diff-Serv Tunneling Model use case as defined in [RFC3270].
In this case the topmost label can be preserved Ultimate Hop POP
(UHP) to the egress PE. With the Default implicit-null Penultimate
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Hop (PHP) mode, the egress LSR P node would POP the topmost label
revealing the native IPv4 packet which would be subsequently dropped
as the Core underlay is an IPv6-Only core. There maybe cases where
implicit null value 3 is not signaled by the egress PE either by
default. In such case the implicit null is not signaled to the PHP
node and thus is disabled. In this particular case explicit null
label and Pipe mode Diff-Serv Tunneling Model is not necessary as the
topmost label remains intact and preserved to the egress PE using any
"arbitrary label".
BGP/MPLS VPN [RFC4364] defines 3 label allocation modes for Layer L2
and 3 VPN's as follows: 1. Per Prefix label allocation mode where
all prefixes are labeled. 1. Per-CE label allocation mode where all
prefixes from a CE next hop are given the same label. 2. 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 also applicable to the 4PE. The two level label
stack using a per prefix label allcoation mode is what is used in 6PE
[RFC4798] with a requirement to label all the IPv6 prefixes using
BGP-LU [RFC8277]. 4PE 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. 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. The LSR 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 used.
5. 4PE SR-MPLS Support
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. The
4PE BGP overlay the design for SR-MPLS is identical to MPLS where the
Ingress and Egress PE and the IPv4 NLIR can be optionally labeled.
All else remains the same as far as 4PE and Inter-AS options.
6. 4PE SRv6 Support
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] with the next hop encoding [RFC8950].
7. 4PE Deployment Options
In this section we display all the possible use cases and highlight
the flexiblity of 6PE capabilities and use of 3 different topmost
labaels that can be signaled
[RFC3032] does not require Penultimate Hop POP (PHP) to be enabled by
default. When PHP is not signaled by the egress PE to the PHP node
using implicit null value 3, an arbitrary label can be utilized for
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the topmost label and in that case as PHP is not signaled by the
egress PE node, PHP is not activated and thus the topmost label is
presereved and not popped. Using an arbitarry label eliminates the
need for explicit null value 1 for IPv4 and value 2 for IPv6 to be
imposed as the means to preserve the topmost label for DiffServ PIPE
mode.
* Arbitrary label
* Explicit Null Label for Diffserv PIPE Mode UHP signaling
* Implicit Null label for PHP signaling
In these use cases we dispaly how the IPv4 prefixes tunnled over the
IPv6 LSP can be labed or not labeled
* Labeled IPv4 prefixes
* Unlabeled IPv4 prefixes
All deployment options are applicable to intra-as and inter-as
options A, B, C, AB, with Data planes MPLS, SR-MPLS, SRv6.
7.1. Arbitrary topmost with all customer prefixes labeled
Arbitrary topmost label where LERs signal IPv6 topmost LSP with 2
level label stack BOS set [RFC8277] 1/4 service label labeling all
IPv4 customer prefixes
In this scenario all the attached CE prefixes in the global table are
labled and this is similar to IP-VPN per perfix label allocation
Due to the per prefix label allocation in this scenario it is not as
scalable and convergence maybe slower
7.2. Arbitrary topmost with PE to PE LSP
Arbitrary topmost label where LERs signal IPv6 topmost LSP with 2
level label stack, BOS set [RFC8277] 1/4 service label using ingress
to egress PE loopback to loopback LSP single BOS label with all
global table customer prefixes unlabeled.
In this optimized scenario a single ingrees 4PE to 4PE LSP is created
to carry all the CE prefixes
This sceanario is most optimized from a label allocation perspective
from all other scenarios in that only a single service label is
allocated signaled by the service LSP which now is able to carry all
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of the global table prefixes populated by the attached CE's as
unlabeled IPv4 customer prefixes. This scenario is similar to IP-VPN
Per-VRF Label allocation
This scenario provides per VRF prefix independent BGP PIC Edge like
convergence with Per VRF prefix independence as when the PE LSP is
withdrawn, all attached CE's and related unlabled prefixes are as
well withdrawn further optimizing the convergence and creating per
VRF independence convergence
MPLS label allocation has a 20 bit label name space and thus allows
for a maximum of 1 Millon labels. This is an MPLS protocol limit
that is hardware and software independent. This scenario provides
tremendous scale to the global internet table carried in the default
VRF table now only allocating a single label for all 1 Million
prefixes in the default VRF
7.3. Arbitrary topmost with per CE label table
Arbitrary topmost label where LERs signal IPv6 topmost LSP with 2
level label stack BOS set [RFC8277] 1/4 service label using per CE
label table routing context LSP ingress to egress CE PE-CE interface
PE side interface LSP single BOS label with per CE label table
customer prefixes unlabeled.
This scenario is further optimized by creating a per CE next hop
label table context similar to IP-VPN Per-CE or Per-Next-Hop label
allocation mode where a single label is allocated per CE
In this scenario a single service label is allocated signaled by the
CE interface IP between the ingress 4PE and egreess 4PE creating the
per CE label context service LSP which we are now able to provide per
CE next hop granularity label table context containing the per CE
unlabled customer IPv4 prefixes.
This scenario provides further granularity and per CE independent BGP
PIC Edge like convergence with per CE prefix independence as when the
per CE LSP is withdrawn all the per CE related prefixes are as well
withdrawn further optimizing the convergence and creating per CE
independence granularity with the convergence
7.4. Explicit Null topmost with all customer prefixes labeled
Explicit Null topmost label where LERs signal IPv6 topmost LSP with 2
level label stack BOS set [RFC8277] 1/4 service label labeling all
IPv4 customer prefixes
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In this scenario all the attached CE prefixes in the global table are
labled and this is similar to IP-VPN per perfix label allocation
Due to the per prefix label allocation in this scenario it is not as
scalable and convergence maybe slower
7.5. Explicit Null topmost with PE to PE LSP
Explicit Null topmost label where LERs signal IPv6 topmost LSP with 2
level label stack, BOS set [RFC8277] 1/4 service label using ingress
to egress PE loopback to loopback LSP single BOS label with all
global table customer prefixes unlabeled.
In this optimized scenario a single ingrees 4PE to 4PE LSP is created
to carry all the CE prefixes
This sceanario is most optimized from a label allocation perspective
from all other scenarios in that only a single service label is
allocated signaled by the service LSP which now is able to carry all
of the global table prefixes populated by the attached CE's as
unlabeled IPv4 customer prefixes. This scenario is similar to IP-VPN
Per-VRF Label allocation
This scenario provides per VRF prefix independent BGP PIC Edge like
convergence with Per VRF prefix independence as when the PE LSP is
withdrawn, all attached CE's and related unlabled prefixes are as
well withdrawn further optimizing the convergence and creating per
VRF independence convergence
MPLS label allocation has a 20 bit label name space and thus allows
for a maximum of 1 Millon labels. This is an MPLS protocol limit
that is hardware and software independent. This scenario provides
tremendous scale to the global internet table carried in the default
VRF table now only allocating a single label for all 1 Million
prefixes in the default VRF
7.6. Explicit Null topmost with per CE label table
Explicit Null topmost label where LERs signal IPv6 topmost LSP with 2
level label stack BOS set [RFC8277] 1/4 service label using per CE
label table routing context LSP ingress to egress CE PE-CE interface
PE side interface LSP single BOS label with per CE label table
customer prefixes unlabeled.
This scenario is further optimized by creating a per CE next hop
label table context similar to IP-VPN Per-CE or Per-Next-Hop label
allocation mode where a single label is allocated per CE
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In this scenario a single service label is allocated signaled by the
CE interface IP between the ingress 4PE and egreess 4PE creating the
per CE label context service LSP which we are now able to provide per
CE next hop granularity label table context containing the per CE
unlabled customer IPv4 prefixes.
This scenario provides further granularity and per CE independent BGP
PIC Edge like convergence with per CE prefix independence as when the
per CE LSP is withdrawn all the per CE related prefixes are as well
withdrawn further optimizing the convergence and creating per CE
independence granularity with the convergence
7.7. Implicit Null with all customer prefixes labeled
Implicit Null topmost label where LERs signal IPv6 topmost LSP with 2
level label stack BOS set [RFC8277] 1/4 service label labeling all
IPv4 customer prefixes
In this scenario all the attached CE prefixes in the global table are
labled and this is similar to IP-VPN per perfix label allocation
Due to the per prefix label allocation in this scenario it is not as
scalable and convergence maybe slower
7.8. Implicit Null with PE to PE LSP
Implict Null topmost label where LERs signal IPv6 topmost LSP with 2
level label stack, BOS set [RFC8277] 1/4 service label using ingress
to egress PE loopback to loopback LSP single BOS label with all
global table customer prefixes unlabeled.
In this optimized scenario a single ingrees 4PE to 4PE LSP is created
to carry all the CE prefixes
This sceanario is most optimized from a label allocation perspective
from all other scenarios in that only a single service label is
allocated signaled by the service LSP which now is able to carry all
of the global table prefixes populated by the attached CE's as
unlabeled IPv4 customer prefixes. This scenario is similar to IP-VPN
Per-VRF Label allocation
This scenario provides per VRF prefix independent BGP PIC Edge like
convergence with Per VRF prefix independence as when the PE LSP is
withdrawn, all attached CE's and related unlabled prefixes are as
well withdrawn further optimizing the convergence and creating per
VRF independence convergence
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MPLS label allocation has a 20 bit label name space and thus allows
for a maximum of 1 Millon labels. This is an MPLS protocol limit
that is hardware and software independent. This scenario provides
tremendous scale to the global internet table carried in the default
VRF table now only allocating a single label for all 1 Million
prefixes in the default VRF
7.9. Implicit Null with per CE label table
Implicit Null topmost label where LERs signal IPv6 topmost LSP with 2
level label stack BOS set [RFC8277] 1/4 service label using per CE
label table routing context LSP ingress to egress CE PE-CE interface
PE side interface LSP single BOS label with per CE label table
customer prefixes unlabeled.
This scenario is further optimized by creating a per CE next hop
label table context similar to IP-VPN Per-CE or Per-Next-Hop label
allocation mode where a single label is allocated per CE
In this scenario a single service label is allocated signaled by the
CE interface IP between the ingress 4PE and egreess 4PE creating the
per CE label context service LSP which we are now able to provide per
CE next hop granularity label table context containing the per CE
unlabled customer IPv4 prefixes.
This scenario provides further granularity and per CE independent BGP
PIC Edge like convergence with per CE prefix independence as when the
per CE LSP is withdrawn all the per CE related prefixes are as well
withdrawn further optimizing the convergence and creating per CE
independence granularity with the convergence
7.10. Arbitrary topmost with customer prefixes unlabeled
Arbitrary topmost IPv6 LSP BOS set single level label stack with all
global table customer prefixes 1/1 unlabeled.
This scenario may require some deeper look into the packet Deep
Packet Inspection (DPI) to determine next header inspection for
protocol type so that the packets are not dropped.
7.11. Explicit Null topmost with customer prefixes unlabeled
Explicit null value 2 topmost IPv6 LSP BOS set single level label
stack with all global table customer prefixes 1/1 unlabeled.
This scenario may require some deeper look into the packet Deep
Packet Inspection (DPI) to determine next header inspection for
protocol type so that the packets are not dropped.
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8. Crossing Multiple IPv6 Autonomous Systems
8.1. 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.
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.
8.2. Advertisement of IPv4 prefixes Inter-AS Procedure A
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 scenario, the 4PE router uses iBGP to redistributes labeled
IPv4 prefixes to a Route Reflector or Autonomous System Border Router
(ASBR)4PE router to which an ASBR 4PE router it is a client. The
ASBR then uses eBGP to advertise the (non labeled) IPv4 prefixes to
an ASBR in another AS, which then distributes the IPv4 prefixes to
4PE routers in that AS or further redistributes to subsequent ASBRs
and so on.
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.
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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.
In this design, the ASBR exchanging IPv4 prefixes MUST peer over
IPv4. The exchange of IPv4 prefixes MUST be carried out as per
[RFC4760].
8.3. Advertisement of labeled IPv4 prefixes Inter-AS Procedure B/C
8.3.1. Advertisement of labeled IPv4 prefixes Inter-AS Procedure B
This scenario involves the eBGP redistribution of overlay labeled
IPv4 prefixes between source and destination ASs, along with underlay
eBGP redistribution of labeled unicast IPv6 routes between source and
destination ASs.
This scenario 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 this scenario, the 4PE router uses iBGP to redistributes labeled
IPv4 prefixes to a Route Reflector or Autonomous System Border Router
(ASBR)4PE router to which an ASBR 4PE router it is a client. The
ASBR then uses eBGP to advertise the labeled IPv4 prefixes to an ASBR
in another AS, which then distributes the IPv4 prefixes to 4PE
routers in that AS or further redistributes to subsequent ASBRs and
so on.
There may be one, or multiple, ASBR interconnection(s) across any two
ASes. Thus IPv4 may or may not to be activated on the Inter-AS link
8.3.2. Advertisement of labeled IPv4 prefixes Inter-AS Procedure C
This scenario involves the eBGP multihop redistribution of overlay
labeled IPv4 prefixes between source and destination ASs, along with
underlay eBGP redistribution of labeled unicast IPv6 routes between
source and destination ASs.
This scenario 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.
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In this scenario the ASBRs need not be dual stacked as IPv4 prefixes
redistributed between ASNs are tunneled over IPv6 and thus the IPv4
routes are not maintained or distributed on the 4PE ASBR routers.
The 4PE ASBR only needs to maintain /128 IPv6 routes to all 4PE
routers in its AS so it can redistribute these underlay routes to
other ASs for inter-as reachability. The 4PE ASBRs and any transit
ASBRs will use eBGP to pass along the /128 IPv6 routes to other ASs
in order to create an end to end IPv6 LSP from source AS ingress PE
rouer to destination AS egress PE router. Once the end to end IPv6
LSP is established, the 4PE routers in different ASs can now
establish their eBGP multihop peering over IPv6 and now can exchange
their IPv4 labeled unicast routes over the connection.
IPv4 need not be activated on the Inter-AS ASBR to ASBR, PE to PE
links.
There may be one, or multiple, ASBR interconnection(s) across any two
ASes. IPv4 may or may not be activated on the Inter-AS link.
Note that the 4PE Inter-AS extension for procedure (c) in Section 10
of [RFC4364] that the exchange of IPv4 prefixes can only start after
BGP has established IPv6 connectivity between the ASes.
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].
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
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12.1. Normative References
[I-D.ietf-idr-bgp-sr-segtypes-ext]
Talaulikar, K., Filsfils, C., Previdi, S., Mattes, P., and
D. Jain, "Segment Routing Segment Types Extensions for BGP
SR Policy", Work in Progress, Internet-Draft, draft-ietf-
idr-bgp-sr-segtypes-ext-05, 27 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
sr-segtypes-ext-05>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-segment-
routing-te-policy-26, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-26>.
[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>.
[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>.
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[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., Ed., 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>.
[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>.
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[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>.
[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>.
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[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
[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>.
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[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>.
[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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