Routers operate at layer 3. LAN switches operate at layer 2. Ethernet hubs operate at layer 1.
DHCP
Bridge operate on data link layer
Hubs are a physical layer (layer 1) device; most switches operate at the Data Link layer (Layer 2) of the OSI model.
DHCP runs at the application layer of the OSI model.
Hubs are dumb devices that operate at the hardware layer of the network only. They basically function like an old party line phone system where everything that gets transmitted is sent to every port on the hub and all the connected devices ignore transmissions not sent to them. Hubs are simply not sophisticated enough to offer services and protocols such as DHCP, DNS or any other network protocols themselves. Devices that do offer DHCP are typically routers, some layer 3 switches or servers.
The Transport Layer
UDP and ports 67 and 68.
DHCP is a layer-4 protocol, most commonly transported over UDP. UDP port number 67 is the destination port of a server, and UDP port number 68 is used by the client
Data Link Layer
Hubs and repeaters operate at the Physical Layer of the OSI Model. The Physical Layer is the first layer of the OSI Model.
Layer 3