One embodiment of the present invention provides a switch. The switch is configurable to be a member of a first fabric switch. The switch includes a link aggregation module. During operation, the link aggregation module marks an ingress-switch field of a frame with a virtual switch identifier. This virtual switch identifier is associated with the switch and a second switch, which is a member of a second fabric switch, and is from a range of identifier associated with the first fabric switch and the second fabric switch. Each of the first fabric switch and the second fabric switch is operable to accommodate a plurality of switches and operate as a single switch.