Which Layers Make Up a Layered InfiniBand Network?

The four core InfiniBand layers InfiniBand is a layered fabric architecture whose core layers are the Physical layer (A), Link layer (E), Network layer (B), and Transport layer (C). The Physical layer covers signaling, media, connectors, and per-lane rates. The Link layer handles local switching, flow control, Local Identifiers (LIDs), and Virtual Lanes (VLs). The Network layer provides inter-subnet routing using Global Identifiers (GIDs) and the Global Routing Header (GRH). The Transport layer provides end-to-end message integrity and RDMA operations through Queue Pairs (QPs) and ACK/NAK mechanisms. The application tier (D) is not one of these IB network layers, so the correct selection is A, B, C, and E.

Why the layer mapping matters A supplied community explanation maps Transport to QPs and ACK/NAK, Network to GID and GRH, Link to LID and VL, and Physical to connectors and rate. That mapping is useful because Huawei-style questions often test adjacent distinctions: which layer owns LID versus GID, which layer handles local flow control, and which layer provides reliable end-to-end delivery. It also explains why D is a trap: applications consume InfiniBand Upper Layer Protocols above the transport layer, but an "application tier" is not a peer network layer in the IB stack.

Where the answer could change If an option named "Upper Layer Protocols" or "management layer," do not automatically add it to the four core layers. Upper Layer Protocols sit above transport, and subnet management is a fabric management function rather than one of the core IB layers. If the question instead asked which layer uses GIDs, the answer would be Network; for LIDs and Virtual Lanes, Link; for Queue Pairs and RDMA message integrity, Transport. Those scenario shifts are exactly where careless memorization of a fixed four-letter answer fails.

Operational consequence Confusing the layers leads to real design and troubleshooting errors. An engineer might assume a link-layer LID can route across subnets, or treat application/ULP behavior as part of the fabric layer. In Huawei storage environments using InfiniBand, that misunderstanding complicates partition and subnet-manager troubleshooting and can lead to incorrect assumptions about RDMA path behavior. Keep the four-layer model clear: Physical, Link, Network, and Transport, with applications above them.