Patent US 9,762,433

Systems and methods are described to provide fault tolerant folded Clos networks. A folded Clos network is disclosed including a set of tier 1 routers interconnected with a set of tier 2 routers. Tier 1 routers are configured to view a set of tier 2 routers as a single aggregate router. Accordingly, tier 1 routers are unaware of faults between tier 2 routers and additional tier 1 routers. A throwback router is connected to each tier 2 router to facilitate handling of data under such fault conditions. When a tier 2 router receives undeliverable data, the data is passed to a throwback router, which retransmits the data to an additional tier 2 router. Data that is retransmitted multiple times can be disregarded by the throwback router.