s not overloaded while others carry little or no traffic. Local Area Network A group of devices such as computers, printers, and scan- (LAN) ners that can communicate with one another within a limited geographic area, such as a floor, department, or small cluster of buildings. Layer 2 switch (also A switch located in a wiring closet that allows multiple called a switching simultaneous transmissions within a single LAN. Layer 2 switches provide a dedicated connection during an entire transmission. Layer 3 switch (also A switch that routes traffic across the LAN backbone based known as a routing on IP (network) addresses. They are more complex to man- switch) age than Layer 2 switches, but they can use alternate paths if one path is out of service. They are located in data centers and link wiring closets and buildings within a campus. Layer 4 switch (also A switch located at hosting sites and corporate and govern- known as a content ment sites that host their own web pages. Layer 4 switches switch) connect web traffic to the desired web pages by looking at the URL, the web address from which each packet was trans- ferred to the site. Metropolitan Area Networks that can communicate with one another within a Network (MAN) city or a large campus area covering many city blocks. Router Routers carry traffic between LANs, from enterprises to the Internet, and across the Internet. They are more com- plex than switches because they have routing tables with addresses and perform other functions. Routers select the best available path over which to send data. Data Centers and IP Private Branch Exchanges Table 2-2 (Continued) Protocol, Service, or Device Description Server A centrally located computer with common departmental or organizational files such as personnel records, e-mails, sales data, price lists, student information, and medical records. Servers are connected to Layer 2 or Layer 3 switches. Access to servers can be restricted to authorized users only. Virtual Local Area A virtual local area network is made up of 