| Internet-Draft | BGP extensions for BIER-TE | October 2026 |
| Chen, et al. | Expires 21 April 2027 | [Page] |
"Tree Engineering for Bit Index Explicit Replication" (BIER-TE) shares architecture and packet formats with BIER. BIER-TE forwards and replicates packets based on a BitString in the packet header, but every BitPosition of the BitString of a BIER-TE packet indicates one or more adjacencies.¶
This document describes BGP extensions for advertising the BIER-TE specific information.¶
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"Tree Engineering for Bit Index Explicit Replication" (BIER-TE) shares architecture and packet formats with BIER as described in [RFC8279]. BIER-TE forwards and replicates packets based on a BitString in the packet header, but every BitPosition of the BitString of a BIER-TE packet indicates one or more adjacencies as described in [RFC9262].¶
This document describes BGP extensions for advertising the BIER-TE specific information. More specifically, in this document, we define a new optional, non-transitive BGP attribute, referred to as the BIER-TE attribute, to convey the BIER-TE specific information.¶
These extensions are applicable to BGP based network scenarios.¶
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.¶
[RFC9793] defines BIER Path attribute, and this document reuse the Bier Path attribute. The content of the BIER Path attribute is one or more BIER-TE TLV as shown in Figure 1. This TLV contains BIER-TE information associated with a Prefix.¶
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 (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-domain-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BIER-TE TLV
¶
Type:A 2-octet field with value TBD1, see IANA Considerations section.¶
Length: 2 octets.¶
Subdomain-id: Unique value identifying the BIER-TE sub-domain, 1 octet.¶
Sub-TLVs: contains one or more sub-TLV. In this document, it defines three sub-TLV: the BIER-TE MPLS Encapsulation sub-TLV , the BIER-TE non-MPLS Encapsulation sub-TLV and the Bitposition sub-TLV.¶
This sub-TLV carries the information for the BIER MPLS encapsulation including the label range for a specific BitString length for a certain < MT,SD >. It is advertised within the BIER-TE TLV. This sub-TLV MAY appear multiple times within a single BIER-TE sub-TLV. If the same BitString length is repeated in multiple sub-TLVs inside the same BIER-TE TLV, the BIER-TE TLV MUST be ignored.¶
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: BIER-TE MPLS Encapsulation sub-TLV
¶
Type:A 2-octet field with value TBD2.¶
Length:4¶
Max SI: Maximum Set Identifier (Section 1 of [RFC8279]) used in the encapsulation for this BIER subdomain for this BitString length, 1 octet. Each SI maps to a single label in the label range. The first label is for SI=0, the second label is for SI=1, etc. If the label associated with the Maximum Set Identifier exceeds the 20-bit range, the sub-sub-TLV MUST be ignored.¶
Local BitString Length (BS Len): Encoded BitString length as per [RFC8296]. 4 bits.¶
Label: First label of the range, 20 bits. The labels are as defined in [RFC8296].¶
The sub-TLV is advertised within the BIER-TE TLV.¶
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | BIFT-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: BIER-TE non-MPLS Encapsulation sub-TLV
¶
Type:A 2-octet field with value TBD3.¶
Length:4¶
Max SI: Maximum Set Identifier (Section 1 of [RFC8279]) used in the encapsulation for this BIER subdomain for this BitString length, 1 octet. The first BIFT-id is for SI=0, the second BIFT-id is for SI=1, etc. If the BIFT-id associated with the Maximum Set Identifier exceeds the 20-bit range, the sub-TLV MUST be ignored.¶
Local BitString Length (BS Len): Encoded BitString length as per [RFC8296]. 4 bits.¶
BIFT-id: A 20 bit field encoding the first BIFT-id of the BIFT-id range. BIFT-id as per [I-D.ietf-bier-lsr-non-mpls-extensions].¶
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitPosition-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adjacency address-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitPosition-n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adjacency address-n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4:Bitposition sub-TLV
¶
Type:A 2-octet field with value TBD4.¶
Length:4 if the Nexthop is IPv4 address and 16 if the Nexthop is IPv6 address¶
<BitPosition,Adjacency address>: A 2-octet field encoding the BitPosition associated with a adjacency address. Each adjacency address is a local or remote neighbor address.¶
The Bitposition sub-TLV is included in the BIER-TE TLV.¶
The authors would like to thank Zhaohui Zhang for his valuable suggestions.¶
The document requests new allocations from the IANA registries as follows:¶
This document requests assigning code-points from the "BGP BIER Path Attribute Types" registry for the new BIER-TE TLV.¶
Value Description Reference --------- --------------------- --------------- TBD1 BIER-TE This document¶
This document requests assigning code-points from the "BGP BIER-TE TLV sub-TLV Types" for the new BIER-TE Encapsulation sub-TLVs.¶
Value Description Reference --------- -------------------------------- --------------- TBD2 BIER-TE MPLS Encapsulation This document TBD3 BIER-TE non-MPLS Encapsulation This document¶
This document requests assigning code-points from the "BGP BIER-TE TLV sub-TLV Types" for the new Bitposition sub-TLV.¶
Value Description Reference --------- ---------------------------- --------------- TBD4 Bitposition sub-TLV This document¶
This document introduces no new security considerations beyond those already discussed in [RFC4271] and [RFC9262].¶