BIER Encapsulation
draft-xu-bier-encapsulation-01

Abstract

Bit Index Explicit Replication (BIER) is a new multicast forwarding paradigm which doesn't require an explicit tree-building protocol and doesn't require intermediate routers to maintain any multicast state. This document proposes a transport-independent BIER encapsulation header which is applicable in any kind of transport networks.

Status of This Memo

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Terminology
• 3. BIER Header
• 4. Transport Encapsulation for BIER Header
• 5. Acknowledgements
• 6. IANA Considerations
• 7. Security Considerations
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

Bit Index Explicit Replication (BIER) [I-D.wijnands-bier-architecture] is a new multicast forwarding paradigm which doesn't require an explicit tree-building protocol and doesn't require intermediate routers to maintain any multicast state. As described in [I-D.wijnands-bier-architecture], BIER requires that a multicast data packet (e.g., an IP packet or an MPLS packet) to be encapsulated with a BIER header that carries the information needed for supporting the BIER forwarding procedures. This information at least includes Set-Identifier (SI), Multi-Topology Identifier (MT-ID) and BitString. The SI and the BitString are used together to identify the set of egress BFRs (BFERs) to which the packet must be delivered. In addition, to indicate what type of payload is following the BIER header, a protocol type field is neccessary. This document proposes a transport-independent BIER encapsulation header which is applicable in any kind of transport networks.

1.1. 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].

2. Terminology

This memo makes use of the terms defined in [I-D.wijnands-bier-architecture].

3. BIER Header

The BIER header is shown as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Ver  |   BS Length   |       SI      |         MT-ID         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           BFIR-ID             |         Protocol Type         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Entropy             |      DS       |      TTL      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                BitString  (first 32 bits)                     ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                BitString  (last 32 bits)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Ver(sion): This 4-bit field identifies the version of the BIER header. This document specifies version 0 of the BIER header.
• BS Length: This 8-bit field indicates the length of the BitString in 4-byte unit. In other words, if the BitString length is 4*n byte, this field should be filled with n (e.g., if the length of the BitString is 32 bits, the length field is set to 1, if the length of the BitString is 64 bits, the length field is set to 2...)
• SI: This 8-bit field is filled with the Set-Identifier (SI) for this packet.
• MT-ID: This 12-bit field indicates which routing topology [RFC4915] [RFC5120] should be applied for BIER forwarding.
• BFIR-ID: This 16-bit field is filled with the BFR-ID of the BFIR.
• Protocol Type: This 16-bit field indicates the protocol type of the BIER payload as per [ETYPES]. The BIER payload types include but not limited to IPv4 packet, IPv6 packet, MPLS packet, VXLAN packet [RFC7348] VXLAN-GPE packet [I-D.quinn-vxlan-gpe], etc. The corresponding Ethertype codes for VXLAN and VXLAN-GPE are TBD1 and TBD2 respectively.
• Entropy: This 16-bit field specifies an "entropy" value that can be used for load balancing purposes.
• BitString: The variable-length BitString field that, together with the SI field, identifies all the destination BFERs for this packet.
• DS: The usage of this field is no different from that of the Differentiated Services (DS) field in the IPv4 or IPv6 headers [RFC2474].
• TTL: The usage of this field is no different from that of the Time to Live (TTL) field in the IPv4 header.

4. Transport Encapsulation for BIER Header

Since the BIER encapsulation format as specified in Section 3 is transport-independent, it can be encapsulated with any type of transport encapsulation headers, such as Ethernet header, PPP header, IP header, MPLS header, GRE header, UDP header etc. It requires for each possible transport encapsulation header to be able to indicate the payload is an BIER header. For instance, In the BIER-in-MAC encapsulation case, the EtherType field in the Ethernet header is used. In the BIER-in-IP encapsulation case, the Protocol or Next-Header field in the IPv4 or IPv6 header is used. In the BIER-in-MPLS encapsulation case, either the Protocol Type field [I-D.xu-mpls-payload-protocol-identifier] within the MPLS packet or a to-be-assigned Extended Spcial Purpose label [RFC7274] is used.

5. Acknowledgements

TBD.

6. IANA Considerations

This document includes a request to IANA to allocate an EtherType code,a PPP protocol code, an IPv4 protocol code, an IPv6 Next-Header code, a UDP destination port for carring the BIER-encapsulated packet over the corresponding transport networks. Furthermore, This document includes a request to IANA to allocate EtherType codes for VXLAN and VXLAN-GPE respectively.

7. Security Considerations

TBD.

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses