BGP Extensions for BIER
draft-xu-idr-bier-extensions-00

Abstract

Bit Index Explicit Replication (BIER) is a new multicast forwarding architecture which doesn't require an explicit tree-building protocol and doesn't require intermediate routers to maintain any multicast state. BIER is applicable in a multi-tenant data center network envioronment for efficient delivery of Broadcast, Unknown-unicast and Multicast (BUM) traffic while eliminating the need for maitaining a huge amount of multicast state in an underlay. This document describes BGP extensions for advertising the BIER-specific information. These extesnions are applicable in those multi-tenant data centers where BGP instead of IGP is deployed as an underlay for network reachability advertisement. These extensions may also be applicable in other scenarios.

Status of This Memo

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This Internet-Draft will expire on August 20, 2015.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Terminology
• 3. BIER Path Attribute
• 4. Originating BIER Attribute
• 5. Restrictions on Sending/Receiving
• 6. Acknowledgements
• 7. IANA Considerations
• 8. Security Considerations
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

1. Introduction

Bit Index Explicit Replication (BIER) [I-D.wijnands-bier-architecture] is a new multicast forwarding architecture which doesn't require an explicit tree-building protocol and doesn't require intermediate routers to maintain any multicast state. BIER is applicable in a multi-tenant data center network envioronment for efficient delivery of Broadcast, Unknown-unicast and Multicast (BUM) traffic while eliminating the need for maitaining a huge amount of multicast state in an underlay[I-D.kumar-bier-use-cases]. This document describes BGP extensions for advertising the BIER-specific information. More specifically, in this document, we define a new optional, non-transitive BGP attribute, referred to as the BIER attribute, to convey the BIER-specific information such as BFR-ID, bitstring length and so on. In addition, this document specifies procedures to prevent the BIER attribute from "leaking out" of a BIER domain . These extensions are applicable in those multi-tenant data centers where BGP instead of IGP is used as an underlay [I-D.ietf-rtgwg-bgp-routing-large-dc]. These extensions may also be applicable to other BGP based network scenarios.

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 [RFC4271].

3. BIER Path Attribute

This draft defines a new optional, transitive BGP path attribute, referred to as the BIER attribute. This attribute can be attached to a BGP UPDATE message by the originator so as to indicate the BIER-specific information of a particular BFR which is identified by the /32 or /128 address prefix contained in the NLRI.

The attribute type code for the BIER Attribute is TBD. The value field of the BIER Attribute is defined here to contain a set of TLVs. Each such TLV is encoded as shown in Figure 1.

       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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |         Length                |               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
       ~                                                               ~
       |                           Value                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..........................
                             Figure 1:BIER TLV                                 

[I-D.wijnands-mpls-bier-encapsulation]. Other TLVs are to be defined in the future.

• Type: A single octet encoding the TLV Type.
• Length: A single octet encoding the length in octets of the TLV, including the type and length fields. The length is encoded as an unsigned binary integer. (Note that the minimum length is 3, indicating that no value field is present.)
• Value: A variable-length field containing zero or more octets.

This document defines three such TLVs including "BFR-ID TLV" , "BSL TLV" and "MPLS BIER Encapsulation TLV". The first one is used to convey the BFR-ID of the BFR which is indicated by the NLRI. The second one is used to indicate the BitString Length that the BFR which is indicated by the NLRI can support. The third one is used to indicate the MPLS label range available for the MPLS-BIER encapsulation purpose

The BFR-ID TLV is encoded as follows:

• Type:TBD2
• Length:5
• Value: contains a two-octet BFR-ID

The BSL TLV is encoded as follows:

• Type:TBD3
• Length:4
• Value: contains a one-octet BSL which indicates the length of the Bitstring in 4-octets.

The BIER MPLS Encapsualtion TLV is encoded as follows:

• Type:TBD4
• Length:5
• Value: contains a one-octet Label Range Size field indicating the size of the label range, and a 3-octect Label Rang Base field where the 20 rightmost bits represent the first label in the label range.

4. Originating BIER Attribute

An implementation that supports the BIER attribute MUST support a policy to enable or disable the creation of the BIER attribute and its attachment to specific BGP routes. An implementation MAY disable the creation of the BIER attribute unless explicitly configured to do so otherwise. A BGP speaker MUST only attach the locally created BIER attribute to a BGP UPDATE message in which one of its local addresses (e.g., a loopback address) is contained in the NLRI.

5. Restrictions on Sending/Receiving

An implementation that supports the BIER attribute MUST support a per-EBGP-session policy, that indicates whether the attribute is enabled or disabled for use on that session. The BIER attribute MUST NOT be sent on any EBGP peers for which the session policy is not configured. If an BIER attribute is received on a BGP session for which session policy is not configured, then the received attribute MUST be treated exactly as if it were an unrecognized non-transitive attribute. That is, "it MUST be quietly ignored and not passed along to other BGP peers".

To prevent the BIER attribute from "leaking out" of an BIER domain, each BGP router on the BIER domain MUST support an outbound route announcement policy.Such a policy MUST be disabled on each EBGP session by default unless explicitly configured.

6. Acknowledgements

TBD.

7. IANA Considerations

IANA is requested to assign a codepoint in the "BGP Path Attributes" registry to the BIER attribute. IANA shall create a registry for "BGP BIER Attribute Types". The type field consists of a single octet, with possible values from 1 to 255. (The value 0 is "reserved".) The allocation policy for this field is to be "Standards Action". Type codes should be allocated for BFR-ID TLV, BSL TLV and BIER MPLS Encapsualtion TLV respectively.

8. Security Considerations

TBD.

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses