Less and less every year. Five years ago the entire DC used third-party networking gear from top to bottom. The top of rack switch was the first thing to go,

Less and less every year. Five years ago the entire DC used third-party networking gear from top to bottom. The top of rack switch was the first thing to go, replaced with an in-house device that could do the job well and that provided flexibility for future plans. Load balancers (there was almost a contest to see who could get to be the ones to take a sledgehammer to those F5 pieces of shit) and cluster switches were next; at that point you had an entire fabric of custom-made kit that would do rack-level BGP. Intra-cluster and gateway switches are the remaining big iron, or at least were when I left, and I am not sure it will ever be worthwhile for Facebook to invest in the hardware necessary for those tasks. Expensive kit for sure, but the spend with third-party networking gear companies dropped by at least an order of magnitude over less than a decade.