Create a LAN (7.3)–Cisco Routing Between Networks Layer

Create a LAN (7.3)–Cisco Routing Between Networks Layer

End devices, both clients and servers, are connected to LANs. The LAN is how users access the network and reach other networks.

Local-Area Networks (7.3.1)

The term local-area network (LAN) refers to a local network or a group of interconnected local networks that are under the same administrative control, as shown in Figure 7-11. In the early days of networking, LANs were defined as small networks that existed in a single physical location. Although LANs can be a single local network installed in a home or small office, the definition of LAN has evolved to include interconnected local networks consisting of many hundreds of hosts, installed in multiple buildings and locations.

   

Figure 7-11 Collection of Local Networks Under the Same Administrative Control

The important thing to remember is that all the local networks within a LAN are under one administrative control. Other common characteristics of LANs are that they typically use Ethernet or wireless protocols, and they support high data rates.

The term intranet is often used to refer to a private LAN that belongs to an organization and is designed to be accessible only by the members of the organization, employees, or others with authorization.

Local and Remote Network Segments (7.3.2)

Within a LAN, it is possible to place all hosts on a single local network or divide them between multiple networks connected by a distribution layer device. How this placement is determined depends on the desired results.

All Hosts in One Local Segment

Placing all hosts on a single local network allows them to be seen by all other hosts, as shown in Figure 7-12. The reason is that there is one broadcast domain and hosts use ARP to find each other.

   

Figure 7-12 A Local Segment

In a simple network design, it may be beneficial to keep all hosts within a single local network. However, as networks grow in size, increased traffic decreases network performance and speed. In this case, it may be beneficial to move some hosts onto a remote network.

Advantages of a single local segment:

• Appropriate for simple networks
• Less complexity and lower network administrative cost
• The capability of devices to be “seen” by other devices
• Faster data transfer—more direct communication
• Ease of device access

Disadvantages of a single local segment:

• All hosts are in one broadcast domain, which causes more traffic on the segment and may slow network performance.
• Implementing quality of service (QoS) is harder; QoS gives priority to certain types of messages during times of network congestion.
• Implementing security is harder.

Hosts on a Remote Segment

Placing additional hosts on a remote network decreases the impact of traffic demands, as shown in Figure 7-13. However, hosts on one network are not able to communicate with hosts on the other without the use of routing. Routers increase the complexity of the network configuration and can introduce latency, or time delay, on packets sent from one local network to the other.

   

Figure 7-13 Router Segmenting the Local Network

Advantages:

• Is more appropriate for larger, more complex networks
• Splits up broadcast domains and decreases traffic
• Can improve performance on each segment
• Makes the devices invisible to those on other local network segments
• Can provide increased security
• Can improve network organization

Disadvantages:

• The use of routing is required (at the distribution layer).
• The router can slow traffic between segments.
• It is more complex and expensive (because a router is required).

Packet Tracer—Observe Data Flow in a LAN (7.3.3)

In this activity, you will complete the following objectives:

• Develop an understanding of the basic functions of Packet Tracer.
• Create/model a simple Ethernet network using three hosts and a switch.
• Observe traffic behavior on the network.
• Observe data flow of ARP broadcasts and pings.

Lab—Connect to a Wireless Router (7.3.4)

In this lab, you will complete the following objectives:

• Connect a PC to a wireless router using an Ethernet cable.
• Configure the PC with an appropriate IP address.
• Verify the PC configuration using a command prompt.

Summary (7.4)

The following is a summary of each topic in the chapter:

• The Need for Routing—As networks grow, you may need to divide one access layer network into multiple access layer networks. The distribution layer connects these independent local networks and controls the traffic flowing between them. It is responsible for ensuring that traffic between hosts on the local network stays local. Networking devices that make up the distribution layer are designed to interconnect networks, not individual hosts.

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, routing is needed. Routing is the process of identifying the 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 destination Layer 3 IP address.

• The Routing Table—Each port, or interface, on a router connects to a different local network. Every router contains a table of all locally connected networks and the interfaces that connect to them. These routing tables can also contain information about the routes that the router uses to reach other remote networks. A router forwards a packet to one of two places: a directly connected network containing the destination host or to another router on the path to reach the destination host. When a router encapsulates the frame to forward it out of an Ethernet interface, it must include a destination MAC address. This is the MAC address of the destination host, if the destination host is part of a network locally connected to the router. If the router must forward the packet to another router through an Ethernet interface, it uses the MAC address of the connected router. Routers obtain these MAC addresses from ARP tables.

Routing tables contain the addresses of networks and the path to reach those networks. Entries can be made to the routing table in two ways: dynamically updated by information received from other routers in the network or manually entered by a network administrator.

How does the source host determine the MAC address of the router? A host is given the IPv4 address of the router through the default gateway address configured in its TCP/IP settings. The default gateway address is the address of the router interface connected to the same local network as the source host.

• Create a LAN—The LAN refers to a local network or a group of interconnected local networks that are under the same administrative control. Other common characteristics of LANs are that they typically use Ethernet or wireless protocols, and they support high data rates.

In a simple network design, it may be beneficial to keep all hosts within a single local network. Placing some hosts on a remote network decreases the impact of traffic demands. However, hosts on one network are not able to communicate with hosts on the other without the use of routing.