Physical Locations–Cisco Routing Between Networks Layer
Routers in the distribution layer can be used to interconnect local networks at various locations of an organization that are geographically separated, as shown in Figure 7-3.
Figure 7-3 Routers Connecting Two Sites
Logical Grouping
Routers in the distribution layer can be used to logically group users, such as departments within a company, who have common needs or for access to resources, as shown in Figure 7-4.
Figure 7-4 Logically Separating Users into Groups
When Routing Is Needed (7.1.3)
In most situations, you want your devices to be able to connect beyond your local network: out to other homes, businesses, and the Internet. Devices that are beyond the local network segment are known as remote hosts. When a source device sends a packet to a remote destination device, the help of routers and routing is needed. Routing is the process of identifying the best path to a destination.
A router is a networking device that connects multiple Layer 3 IP networks. At the distribution layer of the network, routers direct traffic and perform other functions critical to efficient network operation. Routers, like switches, are able to decode and read the messages that are sent to them. Unlike switches, which make their forwarding decision based on the Layer 2 MAC address, routers make their forwarding decision based on the Layer 3 IP address, as shown in Figure 7-5.
Figure 7-5 IP Packet Encapsulated in an Ethernet Frame
The packet format contains the IP addresses of the destination and source hosts, as well as the message data being sent between them. The router reads the network portion of the destination IP address and uses it to find which one of the attached networks is the best way to forward the message to the destination.
Any time the network portion of the IP addresses of the source and destination hosts do not match, a router must be used to forward the message. If a host located on network 1.1.1.0 needs to send a message to a host on network 5.5.5.0, the host forwards the message to the router. The router receives the message, de-encapsulates the Ethernet frame, and then reads the destination IP address in the IP packet. It then determines where to forward the message. It re-encapsulates the packet back into a new frame and forwards the frame on to its destination.
Lab—IPv4 Addresses and Network Communication (7.1.4)
In this lab, you will complete the following objectives:
- Build a simple peer-to-peer network and verify physical connectivity.
- Assign various IP addresses to hosts and observe the effects on network communication.