Ethernet Networks PDF - St. John Paul II College of Davao

ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Week 7 Lesson Title Ethernet Networks...

ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Week 7 Lesson Title Ethernet Networks Explain how communication occurs on Ethernet Learning Outcome(s) networks. At SJPIICD, I Matter! LEARNING INTENT! Terms to Ponder Encapsulation is the process of placing one message format inside another message format. MAC Address is the media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. Hierarchical Design Model is a network model that is used to design and engineer data communication networks. Collision domain is a network segment connected by a shared medium or through repeaters where simultaneous data transmissions collide with one another. Broadcasting is sending data packets to multiple recipients all at once. Address Resolution Protocol (ARP) is a procedure for mapping a dynamic Internet Protocol address (IP address) to a permanent physical machine address in a local area network (LAN). A physical address or the MAC address indicates the individual identity of a specific host, but it does not indicate where on the network the host is located. A logical address or the IP address is assigned logically based on where the host is located. Routing (router is the device) is the process of identifying the best path to a destination. Essential Content How do Ethernet Network Work? Preparing Data for Transmission: Encapsulation When sending a letter, the letter writer uses an accepted format to ensure that the letter is delivered and understood by the recipient. In the same way, a message that is sent over a computer network follows specific format rules in order for it to be delivered and processed. The process of placing one message format (the letter) inside another message format (the envelope) is called encapsulation. De-encapsulation occurs when the process is reversed by the recipient and the letter is removed from the envelope. Just as a letter is SCP-NET101 | 139  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached encapsulated in an envelope for delivery, so computer messages are encapsulated. Each computer message is encapsulated in a specific format, called a frame, before it is sent over the network. A frame acts like an envelope; it provides the address of the intended destination and the address of the source host. The format and contents of a frame are determined by the type of message being sent and the channel over which it is communicated. Messages that are not correctly formatted are not successfully delivered to or processed by the destination host. Framing the Message The Ethernet protocol standards define many aspects of network communication including frame format, frame size, timing and encoding. When messages are sent between hosts on an Ethernet network, the hosts format the messages into the frame layout that is specified by the standards. Frames are also referred to as Layer 2 Protocol Data Units (PDUs). This is because the protocols that provide the rules for the creation and format of the frame perform the functions that are specified at the data link layer (Layer 2) of the OSI model. The format for Ethernet frames specifies the location of the destination and source MAC addresses, and additional information including: Preamble for sequencing and timing - defined pattern of alternating 1 and 0 bits used to synchronize timing Start of frame delimiter - marks the end of the timing information and start of the frame The Destination MAC Address field - contains the destination MAC address (receiver). The destination MAC address can be unicast, which is a specific host, multicast, which is a group of hosts, or broadcast, which is all hosts on the local network. The Source MAC Address field - contains the source MAC address, which is the sender. This is the unicast address of the Ethernet host that transmitted the frame. Length and type of frame - supports two different uses. A type value indicates which protocol will receive the data. The length indicates the number of bytes of data that follows this field. The Data field - contains the packet of information being sent. Ethernet requires each frame to be between 64 and 1518 bytes. Frame check sequence - to detect transmission errors also called the CRC Checksum. The F.C.S. contains a 4-byte value that is created by the device that sends data and is recalculated by the destination device to check for damaged frames. The size of Ethernet frames is normally limited to a maximum of 1518 bytes and a minimum size of 64 bytes from the Destination MAC Address field through the Frame Check Sequence. The preamble and the SFD are used to indicate the beginning of the frame. They are not used in the calculation of the frame size. Frames that do not match these limits are not processed by the receiving hosts. SCP-NET101 | 140  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached In addition to the frame formats, sizes and timing, Ethernet standards define how the bits making up the frames are encoded onto the channel. Bits are transmitted as either electrical impulse over copper cable or as light impulses over fiber-optic cable. The Building Blocks of Ethernet Networks Why Networks Need Hierarchical Design On an Ethernet network, the host MAC address is similar to a person's name. A MAC address indicates the individual identity of a specific host, but it does not indicate where on the network the host is located. If all hosts on the Internet (millions and millions of them) were each identified by only their unique MAC address, imagine how difficult it would be to locate a single one. Additionally, Ethernet technology generates a large amount of broadcast traffic in order for hosts to communicate. Broadcasts are sent to all hosts within a single network. Broadcasts consume bandwidth and slow network performance. What would happen if the millions of hosts attached to the Internet were all in one Ethernet network and were using broadcasts? For these two reasons, large Ethernet networks consisting of many hosts are not efficient. It is better to divide larger networks into smaller, more manageable pieces. One way to divide larger networks is to use a hierarchical design model. Benefits of a Hierarchical Design In networking, hierarchical design is used to group devices into multiple networks that are organized in a layered approach. This method of designing networks consists of smaller, more manageable groups that allow local traffic to remain local. Only traffic that is destined for other networks is moved to a higher layer. A hierarchical, layered design provides increased efficiency, optimization of function, and increased speed. It allows the network to scale as required because additional local networks can be added without impacting the performance of the existing ones. As shown in the figure, the hierarchical design has three basic layers: SCP-NET101 | 141  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Access Layer – This layer provides connections to hosts in a local Ethernet network. Distribution Layer – This layer interconnects the smaller local networks. Core Layer – This layer provides a high-speed connection between distribution layer devices. With a hierarchical design, there is a need for a logical addressing scheme that can identify the location of a host. The most common addressing scheme on the Internet is Internet Protocol version 4 (IPv4). Internet Protocol version 6 (IPv6) is the network layer protocol currently being implemented as a replacement to IPv4. Logical Addressing Physical and Logical Addresses A person's name usually does not change. A person's address on the other hand, relates to where they live and can change. On a host, the MAC address does not change; it is physically assigned to the host NIC and is known as the physical address. The physical address remains the same regardless of where the host is placed on the network. The IP address is similar to the address of a person. It is known as a logical address because it is assigned logically based on where the host is located. The IP address, or network address, is assigned to each host by a network administrator based on the local network. IP addresses contain two parts. One part identifies the local network. The network portion of the IP address will be the same for all hosts connected to the same local network. The second part of the IP address identifies the individual host. Within the same local network, the host portion of the IP address is unique to each host. Both the physical MAC and logical IP addresses are required for a computer to communicate on a hierarchical network, just like both the name and address of a person are required to send a letter. SCP-NET101 | 142  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached How are Networks Built? Starting with a Good Design Access, Distribution and Core IP traffic is managed based on the characteristics and devices associated with each of the three layers of the hierarchical network design model: Access, Distribution and Core. Access Layer The access layer provides a connection point for end user devices to the network and allows multiple hosts to connect to other hosts through a network device, usually a switch or access point. Typically, all devices within a single access layer will have the same network portion of the IP address. If a message is destined for a local host, based on the network portion of the IP address, the message remains local. If it is destined for a different network, it is passed up to the distribution layer. Switches provide the connection to the distribution layer devices, usually a router. Distribution Layer The distribution layer provides a connection point for separate networks and controls the flow of information between the networks. It typically contains more powerful switches than the access layer as well as routers for routing between networks. Distribution layer devices control the type and amount of traffic that flows from the access layer to the core layer. Core Layer The core layer is a high-speed backbone layer with redundant (backup) connections. It is responsible for transporting large amounts of data between multiple end networks. Core layer devices typically include very powerful, high- speed switches and routers. The main goal of the core layer is to transport data quickly. SCP-NET101 | 143  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Access Layer Devices The access layer is the basic level of the network. It is the part of the network in which people gain access to other hosts and to shared files and printers. The access layer provides the first line of networking devices that connect hosts to the wired Ethernet network. Networking devices enable us to connect many hosts with each other and also provide those hosts access to services offered over the network. Unlike the simple network consisting of two hosts connected by a single cable, in the access layer, each host is connected to a networking device. This type of connectivity is shown in the figure. Within an Ethernet network, each host is able to connect directly to an access layer networking device using an Ethernet cable. These cables are manufactured to meet specific Ethernet standards. Each cable is plugged into a host NIC and then into a port on the networking device. There are several types of networking devices that can be used to connect hosts at the access layer, including Ethernet switches. Ethernet Hubs The original Ethernet networks connected all hosts with a single cable, similar to how cable TV cables are connected in your home. All users on the network shared the bandwidth available on the cable. As Ethernet networks became more popular, connecting everyone on a single cable was no longer practical, nor even possible. Engineers developed a different type of network technology that made it easier to connect and reconnect multiple devices to the network. The first of these types of networking devices were Ethernet Hubs. Hubs contain multiple ports that are used to connect hosts to the network. Hubs are simple devices that do not have the necessary electronics to decode the messages sent between hosts on the network. Hubs cannot determine which host should get any particular message. A hub simply accepts electronic signals from one port and regenerates (or repeats) the same message out all of the other ports. All hosts attached to the hub share the bandwidth, and will receive the message. Hosts ignore the messages that are not addressed to them. Only the host specified in the destination address of the message processes the message and responds to the sender. Only one message can be sent through an Ethernet hub at a time. SCP-NET101 | 144  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached It is possible for two or more hosts connected to a hub to attempt to send a message at the same time. If this happens, the electronic signals that make up the messages collide with each other at the hub. This is known as a collision. The message is unreadable by hosts and must be retransmitted. The area of the network where a host can receive a garbled message resulting from a collision is known as a collision domain. Because excessive retransmissions can clog up the network and slow down network traffic, hubs are now considered obsolete and have been replaced by Ethernet switches. Ethernet Switches An Ethernet switch is a device that is used at the access layer. When a host sends a message to another host connected to the same switched network, the switch accepts and decodes the frames to read the physical (MAC) address portion of the message. A table on the switch, called a MAC address table, contains a list of all of the active ports and the host MAC addresses that are attached to them. When a message is sent between hosts, the switch checks to see if the destination MAC address is in the table. SCP-NET101 | 145  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached If it is, the switch builds a temporary connection, called a circuit, between the source and destination ports. This new circuit provides a dedicated channel over which the two hosts can communicate. Other hosts attached to the switch do not share bandwidth on this channel and do not receive messages that are not addressed to them. A new circuit is built for every new conversation between hosts. These separate circuits allow many conversations to take place at the same time, without collisions occurring. Ethernet switches also allow for the sending and receiving of frames over the same Ethernet cable simultaneously. This improves the performance of the network by eliminating collisions. MAC Address Tables What happens when the switch receives a frame addressed to a new host that is not yet in the MAC address table? If the destination MAC address is not in the table, the switch does not have the necessary information to create an individual circuit. When the switch cannot determine where the destination host is located, it uses a process called flooding to forward the message out to all attached hosts except for the sending host. Each host compares the destination MAC address in the message to its own MAC address, but only the host with the correct destination address processes the message and responds to the sender. SCP-NET101 | 146  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached How does the MAC address of a new host get into the MAC address table? A switch builds the MAC address table by examining the source MAC address of each frame that is sent between hosts. When a new host sends a message or responds to a flooded message, the switch immediately learns its MAC address and the port to which it is connected. The table is dynamically updated each time a new source MAC address is read by the switch. In this way, a switch quickly learns the MAC addresses of all attached hosts. Containing Broadcasts Within the local network it is often necessary for one host to be able to send messages to all the other hosts at the same time. This can be done using a message known as a broadcast. Broadcasts are useful when a host needs to find information without knowing exactly what other host can supply it or when a host wants to provide information to all other hosts in the same network in a timely manner. A message can only contain one destination MAC address. So, how is it possible for a host to contact every other host on the local network without sending out a separate message to each individual MAC? To solve this problem, broadcast messages are sent to a unique MAC address that is recognized by all hosts. The broadcast MAC address is actually a 48- bit address made up of all ones. Because of their length, MAC addresses are usually represented in hexadecimal notation. The broadcast MAC address in hexadecimal notation is FFFF.FFFF.FFFF. SCP-NET101 | 147  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Each F in the hexadecimal notation represents four ones in the binary address. Broadcasts Domains When a host receives a message addressed to the broadcast address, it accepts and processes the message as though the message was addressed directly to it. When a host sends a broadcast message, switches forward the message to every connected host within the same local network. For this reason, a local area network, a network with one or more Ethernet switches, is also referred to as a broadcast domain. If too many hosts are connected to the same broadcast domain, broadcast traffic can become excessive. The number of hosts and the amount of network traffic that can be supported on the local network is limited by the capabilities of the switches used to connect them. As the network grows and more hosts are added, network traffic, including broadcast traffic, increases. To improve performance, it is often necessary to divide one local network into multiple networks, or broadcast domains, as shown in the figure. Routers are used to divide the network into multiple broadcast domains. Communicating at the Access Layer On a local Ethernet network, a NIC only accepts a frame if the destination address is either the broadcast MAC address, or else corresponds to the MAC address of the NIC. Most network applications, however, rely on the logical destination IP address to identify the location of the servers and clients. The figure illustrates the problem that arises if a sending host only has the logical IP address of the destination host. How does the sending host determine what destination MAC address to place within the frame? SCP-NET101 | 148  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached The sending host can use an IPv4 protocol called address resolution protocol (ARP) to discover the MAC address of any host on the same local network. IPv6 uses a similar method known as Neighbor Discovery. How ARP Works ARP uses a three step process to discover and store the MAC address of a host on the local network when only the IPv4 address of the host is known: The sending host creates and sends a frame addressed to a broadcast MAC address. Contained in the frame is a message with the IPv4 address of the intended destination host. Each host on the network receives the broadcast frame and compares the IPv4 address inside the message with its configured IPv4 address. The host with the matching IPv4 address sends its MAC address back to the original sending host. The sending host receives the message and stores the MAC address and IPv4 address information in a table called an ARP table. When the sending host has the MAC address of the destination host in its ARP table, it can send frames directly to the destination without doing an ARP request. Because ARP messages rely on broadcast frames to deliver the requests, all hosts in the local IPv4 network must be in the same broadcast domain SCP-NET101 | 149  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Distributing Messages to Other Networks Dividing the Local Networks As networks grow, it is often necessary to divide one access layer network into multiple access layer networks. There are many ways to divide networks based on different criteria, including: Broadcast containment Routers in the distribution layer can limit broadcasts to the local network where they need to be heard. Although broadcasts are necessary, too many hosts connected on the same local network can generate excessive broadcast traffic and slow down the network. Security requirements Routers in the distribution layer can separate and protect certain groups of computers where confidential information resides. Routers can also hide the addresses of internal computers from the outside world to help prevent attacks, and control who can get into or out of the local network. Physical locations Routers in the distribution layer can be used to interconnect local networks at various locations of an organization that are geographically separated. 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. The distribution layer connects these independent local networks and controls the traffic SCP-NET101 | 150  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached flowing between them. It is responsible for ensuring that traffic between hosts on the local network stays local. Only traffic that is destined for other networks is passed on. The distribution layer can also filter incoming and outgoing traffic for security and traffic management. Networking devices that make up the distribution layer are designed to interconnect networks, not individual hosts. Individual hosts are connected to the network via access layer devices, such as switches. The access layer devices are connected to each other via the distribution layer device, such as a router. Routing In most situations we want our devices to be able to connect beyond our 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, then 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. 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. Anytime 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 needs to send a message to a host on network 5.5.5.0, the host will forward 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. The figure below shows how MAC and IP addresses are used. SCP-NET101 | 151  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Routing Across Networks Selecting a Path How does the router determine what path to send the message to get to the destination network? 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, or paths, that the router uses to reach other remote networks that are not locally attached. When a router receives a frame, it decodes the frame to get to the packet containing the destination IP address. It matches the network portion of the destination IP address to the networks that are listed in the routing table. If the destination network address is in the table, the router encapsulates the packet in a new frame in order to send it out. (Note that it will insert a new destination MAC address as well, and recalculate the FCS field, in the new frame). It forwards the new frame out of the interface associated with the path, to the destination network. The process of forwarding the packets toward their destination network is called routing. Router interfaces do not forward messages that are addressed to the local network broadcast IP address. As a result, local network broadcasts are not sent across routers to other local networks. The figures show how the router forward packets and block broadcasts. SCP-NET101 | 152  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached Building Tables A router forwards a packet to one of two places: a directly connected network containing the actual 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 actual 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, it will use the MAC address of the connected router. Routers obtain these MAC addresses from ARP tables. Each router interface is part of the local network to which it is attached and maintains its own ARP table for that network. The ARP tables contain the MAC addresses and IPv4 addresses of all of the individual hosts on that network. In the figure, if host H1 needs to send a packet to IPv4 address 192.168.1.3., which is host H3, since Ipv4 is in the same local network and the IPv4 and MAC addresses are in the ARP table, it will be forwarded directly. If H1 needs to send a packet to IPv4 address 192.168.2.1., that IPv4 is not in the same local network. This packet must be sent to my default gateway for forwarding. It must have the default gateway IPv4 and MAC address in the ARP table. At the router, host 192.168.2.1 is on a network directly connected on one of the other interfaces. The router will check the ARP table. When the host 192.168.2.1 is located, the packet is forwarded to H4. How Routers use Tables Routers move information between local and remote networks. To do this, routers must use routing tables to store information. Routing tables are not concerned with the addresses of individual hosts. Routing tables contain the addresses of networks and the best 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 SCP-NET101 | 153  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached a network administrator. Routers use the routing tables to determine which interface to use to forward a message to its intended destination. If the router cannot determine where to forward a message, it will drop it. Network administrators configure a routing table with a default route to keep a packet from being dropped because the path to the destination network is not in the routing table. A default route is the interface through which the router forwards a packet containing an unknown destination IP network address. This default route usually connects to another router that can forward the packet towards its final destination network. Connection type - C stands for direct connect Network - the network address Port - Interface used to forward packets to the network Sending to Remote Networks The method that a host uses to send messages to a destination on a remote network differs from the way a host sends messages on the same local network. When a host needs to send a message to another host located on the same network, it will forward the message directly. A host will use ARP to discover the MAC address of the destination host. The IPv4 packet contains the destination IPv4 address and encapsulates the packet into a frame containing the MAC address of the destination and forwards it out. When a host needs to send a message to a remote network, it must use the router. The host includes the IP address of the destination host within the packet just like before. However, when it encapsulates the packet into a frame, it uses the MAC address of the router as the destination for the frame. In this way, the router will receive and accept the frame based on the MAC address. 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. All hosts on the local network use the default gateway address to send messages to the router. SCP-NET101 | 154  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached When the host knows the default gateway IPv4 address, it can use ARP to determine the MAC address. The MAC address of the router is then placed in the frame, destined for another network. It is important that the correct default gateway be configured on each host on the local network. If no default gateway is configured in the host TCP/IP settings, or if the wrong default gateway is specified, messages addressed to hosts on remote networks cannot be delivered. The figure below shows the IP configuration and default gateway address. Local Area Networks 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. In the early days of networking, LANs were defined as small networks that existed in a single physical location. While 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. The important thing to remember is that all of 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. SCP-NET101 | 155  ST. JOHN PAUL II COLLEGE OF DAVAO COLLEGE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY Physically Detached Yet Academically Attached 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 organization's members, employees, or others with authorization. Assigning Hosts to a LAN Within a LAN, it is possible to place all hosts on a single local network or divide them up between multiple networks connected by a distribution layer. The answer depends on desired results. As shown in the figure below, placing all hosts on a single local network allows them to be seen by all other hosts. This is because there is one broadcast domain and hosts use ARP to find each other. 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 will decrease network performance and speed. In this case, it may be beneficial to move some hosts onto a remote network. As shown in the figure below, placing additional hosts on a remote network will decrease the impact of traffic demands. However, hosts on one network will not be 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. SCP-NET101 | 156