Routing is the process of forwarding packets from one network to another, based on the destination IP address1.
Routing occurs at the network layer of the OSI model, which is the third layer from the bottom2.
The network layer is responsible for logical addressing, path selection, and packet delivery across multiple networks2.
Routers are the devices that operate at the network layer and perform routing functions, using protocols such as RIP, OSPF, EIGRP, or BGP23.
The other layers of the OSI model have different roles in the network communication process, such as:
The data link layer is the second layer from the bottom, and it is responsible for framing, addressing, and error detection of data packets over a single network, using protocols such as Ethernet, Wi-Fi, or PPP2.
The transport layer is the fourth layer from the bottom, and it is responsible for ensuring reliable, error-free, and ordered data transfer between devices, using protocols such as TCP or UDP2.
The physical layer is the bottom layer, and it is responsible for transmitting and receiving bits over a physical medium, such as a cable, a fiber, or a wireless signal2. Reference:
1: CompTIA Network+ N10-008 Cert Guide, 1st Edition, Chapter 5: Routing, p. 179
2: CompTIA Network+ N10-008 Cert Guide, 1st Edition, Chapter 1: Introduction to Networks, pp. 22-29
3: CompTIA Network+ N10-008 Cert Guide, 1st Edition, Chapter 5: Routing, pp. 180-191