Network Working Group                                          Sanjay Navin
Internet-Draft                                                 Individual
Intended status: Standards Track
Expires: January 5, 2027                                   July 5, 2026

Filename: draft-sanjay-navin-hir-for-bgp-mvpn-00

          Hierarchical Ingress Replication (HIR)
    Using Inline BGP Route Reflectors for Multicast VPN Services
      over Hierarchical IP-MPLS Transport Networks

Abstract

   This document specifies Hierarchical Ingress Replication (HIR), a
   scalable multicast forwarding mechanism for BGP Multicast VPN (MVPN)
   services over hierarchical IP-MPLS transport networks.

   HIR introduces packet replication at hierarchical inline BGP Route
   Reflectors (RRs) located at Access, Pre-Aggregation, Aggregation,
   and Core transport layers. By combining control-plane route
   reflection with data-plane packet replication, HIR significantly
   reduces ingress router replication overhead, optimizes bandwidth
   utilization, minimizes multicast state, and improves scalability for
   large-scale multicast VPN deployments in service provider and 5G
   transport networks.

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1. Introduction

RFC 6513 and RFC 6514 define procedures for multicast VPN
services using ingress replication. In existing deployments,
packet replication is performed exclusively at the ingress
Provider Edge (PE), resulting in increasing replication load
and bandwidth consumption as multicast receiver populations
grow.

Large-scale IP-MPLS transport networks deployed for IPTV,
mobile backhaul, and 5G transport commonly use hierarchical
Access, Pre-Aggregation, Aggregation, and Core topologies.
These existing transport hierarchies provide natural locations
for multicast replication.

This document specifies Hierarchical Ingress Replication (HIR),
which distributes multicast packet replication across
replication-capable inline BGP Route Reflectors while
remaining compatible with the BGP MVPN architecture.

2. Motivation

Current Ingress Replication has several limitations:

* Replication occurs only at the ingress PE.
* Bandwidth usage increases linearly with receiver count.
* Large IPTV and 5G multicast deployments generate excessive 
  replication.
* Hierarchical transport networks are not leveraged for multicast 
  optimization.

Modern IP-MPLS networks already deploy:

* Access IS-IS Rings
* Pre-Aggregation Rings
* Aggregation Rings
* Core Rings

These topologies naturally support regional multicast replication.

3. Terminology

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 (RFC 2119) and RFC 8174 when, and only when,
they appear in all capitals, as shown here.

4. Proposed Architecture

   
                Core RR (HIR)
                     |
          -----------------------
          |                     |
      Agg RR-1             Agg RR-2
          |                     |
     PreAgg RR             PreAgg RR
          |                     |
     Access RR             Access RR
          |                     |
          PE                    PE
   

Each Route Reflector:

* Acts as a BGP Route Reflector.
* Participates in MPLS forwarding.
* Performs multicast replication.
* Maintains downstream receiver state.

5. Hierarchical Replication

Traditional Ingress Replication:

PE
|
| 
|  
10 replicated MPLS packets

Proposed HIR:

PE
|
One MPLS packet
|
Core RR
|
+---------+
|         |
Agg1     Agg2
|         |
Replicate Replicate

Replication occurs only where traffic diverges.

6. New Node Capability

A new BGP Capability is defined to advertise Hierarchical Replication 
support.

Capability fields include:

* Replication Supported
* Replication Level
* Maximum Replication Fanout
* Available Replication Resources

Replication levels include:

* Access
* Pre-Aggregation
* Aggregation
* Core

7. New PMSI Tunnel Type

Define a new PMSI Tunnel Type:

HIR (Hierarchical Ingress Replication)

Associated PMSI Tunnel Attribute fields include:

* Tunnel Type = HIR
* Replication Node-ID
* Replication Level
* Replication Label
* Replication Tree-ID

8. New BGP Path Attribute

This document defines a new optional transitive BGP Path Attribute named
the Hierarchical Replication Attribute.

Fields include:

* Replication Domain
* Parent RR
* Child RR List
* Replication Preference
* Replication Cost
* IS-IS Area Identifier
* IS-IS Instance Identifier

This attribute enables multicast distribution to follow the hierarchical
IP-MPLS topology.

9. Receiver Aggregation

Access Route Reflectors aggregate receiver membership learned from
downstream PEs before advertising reachability upstream. Instead of
advertising individual receiver state, the Route Reflector advertises
summarized regional multicast interest to reduce control-plane state.

10. NEXT_HOP Self Enhancement

This document proposes that replication-capable inline Route Reflectors
advertise BGP NEXT_HOP SELF toward downstream replication nodes. This
allows multicast traffic to naturally traverse the hierarchical
replication topology while maintaining compatibility with existing
MVPN procedures.

11. MPLS Data Plane

Packet format:

* Transport Label
* Replication Label
* VPN Label
* Multicast Payload

Each replication node:

* Pops the transport label.
* Examines the Replication Label.
* Replicates packets if required.
* Pushes downstream transport labels.

No multicast lookup is required in transit routers.

12. IS-IS Integration

Each IS-IS flooding domain may serve as a replication domain.

Replication occurs only when multicast traffic exits an IS-IS instance,
reducing unnecessary packet duplication while improving ECMP 
utilization and limiting failure domains.

13. Fast Convergence

HIR supports interoperability with:

* BGP PIC
* ADD-PATH
* BFD
* TI-LFA
* SR-MPLS
* BGP-LU

Failure of one replication-capable Route Reflector may be redirected to
an alternate replication node with minimal service disruption.

14. Advantages

* Significant reduction in ingress PE replication load.
* Reduced backbone bandwidth consumption.
* Improved scalability for IPTV and large-scale multicast services.
* Alignment with hierarchical transport architectures.
* Backward compatibility through BGP capability negotiation.
* Incremental deployment alongside existing Ingress Replication.

15. Security Considerations

Replication-capable Route Reflectors SHOULD be authenticated and 
authorized. Implementations SHOULD validate advertised replication
capabilities and protect against spoofed replication state, malformed
control-plane advertisements, and denial-of-service attacks targeting
replication resources.

16. IANA Considerations

This document requests the following assignments from IANA:

* A new BGP Capability Code for Hierarchical Ingress Replication.
* A new PMSI Tunnel Type for Hierarchical Ingress
  Replication (HIR).
* A new Optional Transitive BGP Path Attribute named
  Hierarchical Replication Attribute.

The values are to be assigned by IANA.

17. Future Work

Future work includes:

* Segment Routing MPLS Point-to-Multipoint (P2MP) integration.
* AI-assisted dynamic placement of replication nodes.
* Controller-assisted optimization using BGP-LS and PCEP.
* Multicast network slicing for 5G and 6G transport networks.
* YANG data models and streaming telemetry for operational visibility.

This document extends the existing MVPN architecture by introducing
topology-aware hierarchical replication while preserving 
interoperability with existing BGP MVPN deployments.

18. References

18.1 Normative References

[RFC2119]
Bradner, S.,
"Key words for use in RFCs to Indicate Requirement Levels",
BCP 14, RFC 2119,
DOI: 10.17487/RFC2119,
March 1997.

[RFC8174]
Leiba, B.,
"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words",
BCP 14, RFC 8174,
DOI: 10.17487/RFC8174,
May 2017.

[RFC4271]
Rekhter, Y., et al.,
"A Border Gateway Protocol 4 (BGP-4)",
RFC 4271,
January 2006.

[RFC4760]
Bates, T., et al.,
"Multiprotocol Extensions for BGP-4",
RFC 4760,
January 2007.

[RFC6513]
Rosen, E., Aggarwal, R., et al.,
"Multicast in MPLS/BGP IP VPNs",
RFC 6513,
February 2012.

[RFC6514]
Aggarwal, R., Rosen, E., et al.,
"BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs",
RFC 6514,
February 2012.

[RFC8277]
Rosen, E.,
"Using BGP to Bind MPLS Labels to Address Prefixes",
RFC 8277,
October 2017.

18.2 Informative References

[RFC4364]
Rosen, E., and Y. Rekhter,
"BGP/MPLS IP Virtual Private Networks",
RFC 4364,
February 2006.

[RFC4456]
Bates, T., et al.,
"BGP Route Reflection: An Alternative to Full Mesh IBGP",
RFC 4456,
April 2006.

[RFC5880]
Katz, D., and D. Ward,
"Bidirectional Forwarding Detection (BFD)",
RFC 5880,
June 2010.

[RFC7432]
Sajassi, A., et al.,
"BGP MPLS-Based Ethernet VPN",
RFC 7432,
February 2015.

[RFC7911]
Walton, D., et al.,
"Advertisement of Multiple Paths in BGP",
RFC 7911,
July 2016.

[RFC8402]
Filsfils, C., et al.,
"Segment Routing Architecture",
RFC 8402,
July 2018.

[RFC8660]
Dawra, G., et al.,
"Segment Routing with MPLS Data Plane",
RFC 8660,
December 2019.

[RFC7752]
Gredler, H., et al.,
"North-Bound Distribution of Link-State and Traffic Engineering 
Information Using BGP",
RFC 7752,
March 2016.

[RFC5440]
Vasseur, J.-P., and J. Le Roux,
"Path Computation Element (PCE) Communication Protocol (PCEP)",
RFC 5440,
March 2009.

19. Author's Address

Sanjay Navin

Email: sanjaynavin@iitbombay.org