Pci express fabric routing for a fully-connected mesh topology

A PCIe Fabric comprising:

• an Input/Output (I/O) tier comprising a first IO tier switch and a second IO tier switch;
• a hub tier comprising a plurality of hub tier switches, wherein the plurality of hub tier switches comprises a first hub tier switch and a second hub tier switch, wherein the IO tier is connected to the hub tier;
• wherein the first IO tier switch is configured to:
• receive, from a client, a transaction layer packet (TLP);
• make a first determination that an address in the TLP is not associated with any multicast address range in the first IO tier switch;
• make a second determination that the address in TLP is not associated with any downstream port in the first IO tier switch;
• based on the first and second determinations, route the TLP to the first hub tier switch using a first upstream port on the first IO tier switch;
• wherein the first hub tier switch is configured to:
• receive, from the first IO tier switch, the TLP at a first downstream port;
• make a third determination that the TLP is associated with a first multicast group;
• based on the third determination:
• generate a first rewritten TLP and route the first rewritten TLP to a first target device via a second downstream port on the first hub tier switch, wherein the second downstream port is a subscriber of the first multicast group.