M-LDP Signaling Through BIER Core

Some operators that are using mLDP P2MP LSPs for their multicast transport would like to deploy BIER technology in some segment of their network. This draft explains a method to signal mLDP services through a BIER domain, with minimal disruption and operational impact to the mLDP domain.

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].

Some of the terminology specified in [I-D.draft-ietf-bier- architecture-05] is replicated here and extended by necessary definitions: BIER: Bit Index Explicit Replication (The overall architecture of forwarding multicast using a Bit Position). BFR: Bit Forwarding Router (A router that participates in Bit Index Multipoint Forwarding). A BFR is identified by a unique BFR prefix in a BIER domain. BFIR: Bit Forwarding Ingress Router (The ingress border router that inserts the Bit Map into the packet). Each BFIR must have a valid BFR-id assigned. BFIR is term used for dataplain packet forwarding. BFER: Bit Forwarding Egress Router. A router that participates in Bit Index Forwarding as leaf. Each BFER must have a valid BFR-id assigned. BFER is term used for dataplain packet forwarding. BBR: BIER Boundary router. The router between the LDP domain and BIER domain. IBBR: Ingress BIER Boundary Router. The ingress router from signaling point of view. It maintains mLDP adjacency toward the LDP domain and determines if the mLDP FEC needs to be signaled across the BIER domain via Targeted LDP. EBBR: Egress BIER Boundary Router. The egress router in BIER domain from signaling point of view. It terminates the targeted ldp signaling through BIER domain. It also keeps track of all IBBRs that are part of this p2mp tree BIFT: Bit Index Forwarding Table. BIER sub-domain: A further distinction within a BIER domain identified by its unique sub-domain identifier. A BIER sub-domain can support multiple BitString Lengths. BFR-id: An optional, unique identifier for a BFR within a BIER sub- domain, all BFERs and BFIRs need to be assigned a BFR-id.

|--------BIER-------->|-------------> Datapatah (new)]]> As per figure 1, point-to-multipoint and multipoint-to-multipoint LSPs established via mLDP [RFC6388] can be signaled through a bier domain via Targeted LDP sessions. This procedure is explained in (Using LDP Multipoint Extension on Targeted LDP Sessions). This documents provides details and defines some needed procedures. .

The Ingress BBR (IBBR) is connected to the mLDP domain on downstream and a bier domain on the upstream. To connect the LDP domains via BIER domain, IBBR needs to establish a targeted LDP session with EBBR closest to the root of the P2MP or MP2MP LSP. To do so IBBR will follow procedures in in particular the section "6. targeted mLDP with Multicast Tunneling". The target LDP session can be established manually via configuration or via automated mechanism.

tLDP session can be signaled automatically from every IBBR to the appropriate EBBR. When mLDP FEC arrives to IBBR from LDP domain, IBBR can automatically start a tLDP Session to the EBBR closest to the Root node. Both IBBR and EBBR should be in auto-discovery mode and react to the arriving tLDP Signaling packets (i.e. targeted hellos, keep- alives etc...) to establish the session automatically. The Root node address in the mLDP FEC can be used to find the EBBR. To identify the EBBR same procedures as section 2.1 can be used or the procedures as explained in the appendix A.

If IBBR finds multiple equal cost EBBRs on the path to the Root, it can use a vendor specific algorithm to choose between the EBBRs. These algorithms are beyond the scope of this draft. As an example the IBBR can use the smallest EBBR IP address to establish its mLDP signaling to.

The Egress BBR (EBBR) is connected to the upstream mLDP domain. The EBBR should accept the tLDP session generated form IBBR. It should assign a unique "upstream assigned label" for each arriving FEC generated by IBBRs. The EBBR should follow the procedures with following modifications: The label assigned by EBBR cannot be Implicit Null. This is to ensure that identity of each p2mp and/or mp2mp tunnel in BIER domain is uniquely distinguished. The label can be assigned from a domain-wide Common Block (DCB) The Interface ID TLV, as per should includes a new BIER sub-domain sub- tlv (type TBD) The EBBR will also generate a new label and FEC toward the ROOT on the LDP domain. The EBBR Should stitch this generate label with the "upstream assigned label" to complete the P2MP or MP2MP LSP. With same token the EBBR should track all the arriving FECs and the IBBRs that are generating these FECs. EBBR will use this information to build the bier header for each set of common FEC arriving from the IBBRs.

Upon receiving the "upstream assigned label", IBBR should create its own stitching instruction between the "upstream assigned label" and the down stream signaled label.

On BFIR when the MPLS label for P2MP/MP2MP LSP arrives from upstream, a lookup in ILM table is done and the label is swapped with tLDP upstream assigned label. The BFIR will note all the BFERs that are interested in specific P2MP/MP2MP LSP (as per section 3.2). BFIR will put the corresponding BIER header with bit index set for all IBBRs interested in this stream. BFIR will set the BIERHeader.Proto = MPLS and will forward the BIER packet into BIER domain. In the BIER domain, normal BIER forwarding procedure will be done, as per The BFERs will receive the BIER packet, will look at the protocol of BIER header (MPLS). BFER will remove the BIER header and will do a lookup in the ILM table for the upstream assigned label and perform its corresponding action. It should be noted that these procedures are also valid if BFIR is the ILER and/or BFER is the ELER as per

The above procedures also will work with a mLDP recursive FEC. The root used to determine the EBBR is the outer root of the FEC. The entire recursive FEC needs to be preserve when it is forwarded via tLDP and the label request.

adf A new BIER sub-domain sub- tlv for the interface ID TLV to be assigned by IANA

TBD

Acknowledgments Authors would like to acknowledge Jingrong Xie for his comments and help on this draft.