Connect multiple pis
https://www.raspberrypi.org/forums/viewtopic.php?t=218115
Switch
https://www.amazon.com/TP-Link-Ethernet-Optimization-Unmanaged-TL-SG105/dp/B00A128S24?ref_=Oct_BSellerC_281414_0&pf_rd_p=00c931d7-95e0-59b7-a798-9306a78f0b1e&pf_rd_s=merchandised-search-6&pf_rd_t=101&pf_rd_i=281414&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=2D53DR26Y1D1ASCCFZ8N&pf_rd_r=2D53DR26Y1D1ASCCFZ8N&pf_rd_p=00c931d7-95e0-59b7-a798-9306a78f0b1e