Even easier (buying hubs is hard) and possibly cheaper (switches with mirror ports aren't the cheapest) is to just stick two network cards into your linux box,

Even easier (buying hubs is hard) and possibly cheaper (switches with mirror ports aren't the cheapest) is to just stick two network cards into your linux box, set up a layer-2 bridge and sniff everything going between. CentOS/RedHat derivitives: https://www.banym.de/linux/centos/setup-bridge-device-on-centos https://www.banym.de/linux/centos/setup-bridge-device-on-cen... Debian/Ubuntu: https://wiki.debian.org/BridgeNetworkConnections https://wiki.debian.org/BridgeNetworkConnections