Gateways work on all seven OSI layers . The main job of a gateway is to convert protocols among communications networks.
A network bridge connects multiple network segments at the data link layer (Layer 2) of the OSI model.
Layer 2 (Data Link Layer) http://compnetworking.about.com/cs/internetworking/g/bldef_bridge.htm
No. Hub works only on first layer. On second layer only swithc/bridge works on second layer of OSI model.
hub work at physical layer of osi model
Layer 1 - the physical layer
Layer 4 : The Transport Layer
Layer 7: The Application Layer
physical layer Layer 1
Layer 2 , Data Link Layer
Switches / Bridges and hubs work at data link layer, but there are layer three switches which operate at network layer. Dhruv
Data Link Layer