mLDP

Note:

This feature is currently supported exclusively on 7730 SXR platforms.

Multicast LDP (mLDP) provides extensions to LDP that enable the establishment of point-to-multipoint (P2MP) and multipoint-to-multipoint (MP2MP) LSPs in MPLS networks.

These multicast LSPs can be used to transport IP multicast traffic or to support multicast services within BGP/MPLS Layer 3 VPNs (MVPN).

On SR Linux, mLDP is used as a provider tunnel for NG-MVPN services. See the ‟NG-MVPN” chapter of the ​SR Linux VPN Services Guide for more information.

mLDP operates in downstream unsolicited (DU) mode over LDP IPv4 only. In DU mode, P2MP LSPs are established from the leaf (downstream) nodes to the root (upstream) node.

Any node running LDP can participate in P2MP LSP setup using the mLDP extensions. SR Linux advertises the P2MP capability to LDP peers using the P2MP capability TLV in the LDP initialization message. This TLV is enabled by default and cannot be disabled through configuration.

Note: mLDP is not supported for LDP IPv6.

For IPv4, a node can operate as a root, leaf, Label Switching Router (LSR), or bud on the same P2MP tree.

Table 1. mLDP node roles
Role Function
Root (I-LER) P2MP LSPs have just one ingress (root) node. The root node receives IP multicast traffic and maps the traffic to a P2MP LSP (push). The node may perform MPLS multicast replication.
Leaf (E-LER) P2MP LSPs have multiple egress (leaf) nodes. A leaf node removes data packets from a P2MP LSP (pop) for further processing. The node may perform IP multicast replication.
LSR A transit LSR can reach the root node via a directly connected upstream LSR. A transit LSR also has one or more directly connected downstream LSRs. The LSR swaps the MPLS label and may perform MPLS multicast replication.
Bud A bud node is an egress node, but also a transit node. The node has directly connected receivers and one or more directly connected downstream LSRs.