Extensions to BIER Tree Engineering (BIER-TE) for Large Multicast Domains and 1:1 Protection: Concept, Implementation and Performance

TL;DR

This work describes how existing networking concepts like tunneling, egress protection and BIER-TE-FRR can be combined to achieve the goal of scaling BIER to large networks as the subset mechanism of BIER is not sufficient for that purpose.

Abstract

Bit Index Explicit Replication (BIER) has been proposed by the IETF as a stateless multicast transport technology. BIER adds a BIER header containing a bitstring indicating receivers of an IP multicast (IPMC) packet within a BIER domain. BIER-TE extends BIER with tree engineering capabilities, i.e., the bitstring indicates both receivers as well as links over which the packet is transmitted. As the bitstring is of limited size, e.g., 256 bits, only that number of receivers can be addressed within a BIER packet. To scale BIER to larger networks, the receivers of a BIER domain have been assigned to subsets that can be addressed by a bitstring with a subset ID. This approach is even compliant with fast reroute (FRR) mechanisms for BIER. In this work we tackle the challenge of scaling BIER-TE to large networks as the subset mechanism of BIER is not sufficient for that purpose. A major challenge is the support of a protection mechanism in this context. We describe how existing networking concepts like tunneling, egress protection and BIER-TE-FRR can be combined to achieve the goal. Then, we implement the relevant BIER-TE components on the P4-programmable Tofino ASIC which builds upon an existing implementation for BIER. Finally, we consider the forwarding performance of the prototype and explain how weaknesses can be improved from remedies that are well-known for BIER implementations.

Figures (10)

• Figure 1: The layered BIER architecture as presented by MeLi2020. Traffic sources and destinations are located in the IPMC layer. In the BIER layer, BIER nodes forward and replicate the IPMC packets based on paths from the routing underlay.
• Figure 2: A packet forwarding example in a BIER-TE domain. The link numbers represent their bit position (starting from the least significant) in the header. For readability, the most significant bits belong to the BFER.
• Figure 3: Examples for node and link protection with BIER-TE FRR. With link protection, the packet is rerouted to the next hop via an alternative path. With node protection, the packet is delivered to all relevant next-next hops of the failed node.
• Figure 4: The TNA consists of an ingress block and an egress block separated by the traffic manager. Each block has its own programmable packet parser, MAT and deparser.
• Figure 5: A MAT consists of a composite lookup key that is applied to a packet. If the lookup key matches, a predefined action is executed. The scheme of the MAT is defined in the data plane while its content is filled by the control plane.