BIER IPv6 Encapsulation (BIERv6) Support via IS-IS

This document defines IS-IS extensions to support multicast forwarding using the Bit Index Explicit Replication (BIER) with IPv6 encapsulation (BIERv6). Familiarity with the concept of "BIER specific" IPv6 address introduced in is necessary to understand the extensions specified in this document. The describes how a function can be bound to a special "IPv6 Address" within a special "IPv6 Address Block". The function bound to a special "IPv6 Address" can be used to indicate a special forwarding process in data-plane. The BIER IPv6 encapsulation uses a "BIER specific" IPv6 unicast address configured locally on a BIER Forwarding Router (BFR) to indicate a "BIER specific handling" in Forwarding Information Base (FIB). This BIER specific IPv6 address is also required to use as the BFR prefix as defined in [RFC8279]. The indication of BFR prefix is a BIER Sub-TLV within the extended IP reachability TLV as specified by in [RFC8401]. The indication of BIER specific function is a "Function Sub-TLV" within the extended IP reachability as specified by in this document. Note the extended IP reachability only includes the TLV 236 (IPv6 IP Reach TLV) [RFC5308] and TLV 237 (MT IPv6 IP Reach TLVs) [RFC5120] in this document. The following restrictions defined for BIER Sub-TLV in section 4.2 of [RFC8401] apply equally to Function Sub-TLV: Prefix length MUST be 128 for an IPv6 prefix. When the Prefix Attributes Flags sub-TLV [RFC7794] is present, the N flag MUST be set and the R flag MUST NOT be set. BIER sub-TLVs and Function Sub-TLVs MUST be included when a prefix reachability advertisement is leaked between levels.

Readers of this document are assumed to be familiar with the terminology and concepts of the documents listed as Normative References.

The Function sub-TLV is introduced to advertise a specified function bound to an IPv6 prefix with 128 bit prefix length. This new sub-TLV is advertised in the TLV 236 or TLV 237. The sub-TLV has the following format:

Type: 1 octet value indicating "Function Information" this IPv6 prefix bound to. To be assigned by IANA. Length: 1 octet length in octets. Value 4 is set to this field. Function: 2 octets value indicating function. A BIER function value called End.BIER defined in is expected to be the only function in the TLV. Flags: 1 octet value indicating the Flags for the function preceding this field. No flags are currently defined and 0 should be set for this field.

The Encapsulation sub-sub-TLV carries the information for the BIER IPv6 encapsulation of a specific BitString length. It is advertised within the BIER Info sub-TLV defined in [RFC8401] which in-turn is carried within the TLVs 236 or 237. This sub-sub-TLV MAY appear multiple times within a single BIER Info sub-TLV. If the same BitString length is repeated in multiple sub-sub-TLVs inside the same BIER Info sub- TLV, the BIER Info sub-TLV MUST be ignored.

The Type field is a 1 octet value indicating BIER IPv6 encapsulation. To be assigned by IANA. The Length field is a 1 octet length in octets. Value 4 is set to this field. Other fields can be referred to [RFC8401] for MPLS encapsulation, or for Ethernet encapsulation.

The procedures of this document do not, in themselves, provide privacy, integrity, or authentication for the control plane or the data plane.

Allocation is expected from IANA for a IS-IS Sub-TLV Type codepoint from the "Sub-TLVs for TLVs 135, 235, 236, and 237" sub-registry. Type: To be assigned by IANA. Description: Function Info. Reference: This document.

Allocation is expected from IANA for a BIER IPv6 encapsulation sub-sub-TLV codepoint from the "sub-sub-TLVs for BIER Info sub-TLV" sub-registry. Type: To be assigned by IANA. Name: BIER IPv6 Encapsulation. Reference: This document.

TBD.