ITE292_SAS_Day11_Network Layer1.pdf

ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class...

ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ Lesson Title: Network Layer Materials: Lesson Targets: SAS At the end of this module, students will be able to: References: 1. Illustrate how network layer protocols and services support  https://www.netacad.com/ communications across data networks. 2. Compare a host routing table to a routing table in a router. 3. Explain how routers enable end-to-end connectivity in a small to medium-sized business network. A. LESSON PREVIEW/REVIEW Introduction Good day, everyone! During our previous meeting, you have learned how the Ethernet sublayers are related to the frame fields and how a switch builds its MAC address table and forwards frames. Also, you have compared the roles of the MAC address and the IP address and learned how ARP requests impact network and host performance. Today, we will learn how network layer protocols and services support communications across data networks and how routers enable end-to-end connectivity in a small to medium-sized business network. Also, you will compare a host routing table to a routing table in a router. So, let's get started! B. MAIN LESSON At OSI Layer 3, the network layer provides services that allow Content and Skill-Building end devices to exchange data across a network. To provide end-to-end transport, the network layer employs four processes: End-device addressing - IP addresses must be unique for identification purposes. Encapsulation - The transport layer protocol data units are encapsulated by including IP header information such as source and destination IP addresses. Routing - The network layer provides services that allow packets to be routed to other networks. Routers determine which path a packet should take to reach its destination network. De-encapsulation - The destination host de-encapsulates the packet to determine whether or not it matches its own. There are several network layer protocols in existence; however, the most commonly implemented are: Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). IP encapsulates the transport layer segment at the network layer by adding an IP header for delivery to the destination host. The IP header remains constant from source to destination host. The process of encapsulating data This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ layer by layer allows services at different layers to scale independently of one another. Routers run multiple network layer protocols concurrently over a network and route traffic using the network layer packet header. Characteristics of IP IP was designed to be a low-overhead protocol, providing only the functions required to deliver a packet from source to destination. Without first establishing a connection, an IP packet is sent to the destination. IP was not intended to track and manage packet flow. Other layers, primarily TCP, perform these functions if necessary. IP- Connectionless IP is a connectionless protocol, which means that no dedicated end-to-end connection is established before data is sent. It is very similar to sending someone a letter via snail mail. Before sending packets, senders have no idea whether the destination is present, reachable, or functional. This attribute contributes to IP's low overhead. IP- Best effort delivery IP is a Best Effort Delivery protocol that is regarded as "unreliable" because it does not guarantee that all packets sent will be received. Unreliable means that IP lacks the ability to manage and recover from undelivered, corrupted, or out-of-order packets. Upper layer protocols/services must resolve issues if packets are missing or not in the correct order at the destination. IP- Media Independent IP operates independently of the media used to transport data at lower layers of the protocol stack; it is unconcerned whether the media is copper cables, fiber optics, or wireless. The OSI data link layer is in charge of preparing the IP packet for transmission over the communications medium. There is a network layer. MTU refers to the maximum This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ size of the PDU that can be transported (maximum transmission unit). The MTU is communicated to the network layer by the data link layer. IPv4 Packet Header An IPv4 packet header is made up of fields that contain binary numbers. These numbers identify various IP packet settings that are examined by the Layer 3 process. Important fields include: Version - Indicates whether the packet is IP version 4 or not. Differentiated Services (DS) - Used to determine the priority of each network packet. Time-to-Live (TTL) - Limits a packet's lifetime and is reduced by one at each router along the way. Protocol - Identifies the next level protocol. Source IPv4 Address - The packet's source address. Destination IPv4 Address - The destination's address. Limitations of IPv4  IP address depletion - The number of unique public IPv4 addresses available in IPv4 is limited. Despite the fact that there are approximately 4 billion IPv4 addresses, the exponential growth of new IPenabled devices has increased the demand.  Internet routing table expansion - A routing table contains the routes to various networks in order to determine the best path. More routes are created as more devices and servers connect to the network. A large number of routes can cause a router to slow down.  Inadequate end-to-end connectivity - Network Address Translation (NAT) was developed to allow devices to share a single IPv4 address. However, because they are shared, they may cause issues for technologies requiring end-to-end connectivity. Introducing IPv6 The IETF began looking for a replacement for IPv4 in the early 1990s, which led to IPv6. The following are some of the advantages of IPv6 over IPv4:  Expanded address space (based on 128-bit addressing as opposed to 32-bit in IPv4)  Improved packet handling - IPv6 has fewer fields than IPv4.  Eliminates the need for NAT - no need to share IPv6 addresses. There are roughly enough IPv6 addresses to go around for every grain of sand on the planet. This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ IPv6 has the following advantages over IPv4 when using the simplified header:  Simplified header format for faster packet processing  Hierarchical network architecture for efficient routing  Address auto-configuration  The need for network address translation (NAT) between private and public addresses is eliminated. Fields in IPv6 packet headers:  Version - A 4-bit binary value set to 0110 identifies the packet as an IPv6 packet.  Traffic Class - an 8-bit field that corresponds to the IPv4 Differentiated Services (DS) field.  Flow Label - This 20-bit field indicates that all packets with the same flow label are handled the same way by routers.  Payload Length - A 16-bit field that indicates the length of the packet's data portion or payload.  Next Header - an 8-bit field that corresponds to the IPv4 Protocol field. It specifies the type of data payload carried by the packet.  Hop Limit - IPv4 TTL field is replaced by an 8-bit hop limit field. As it passes through each router, this value is decremented by one. The packet is discarded when it reaches zero.  Source IPv6 Address - A 128-bit field that identifies the sending host's IPv6 address.  Destination IPv6 Address - A 128-bit field that identifies the receiving host's IPv6 address. Routing The network layer plays an important role in directing packets between hosts. A packet can be sent by a host to: Itself - A host can ping itself for testing purposes by using 127.0.0.1, also known as the loopback interface. Local host - A host that is connected to the same local network as the sending host. The hosts are all assigned the same network address. Remote host - A host on a different network. The hosts have different network addresses. The source IPv4 address and subnet mask are compared to the destination IPv4 address and subnet mask to determine whether the host is on the local or remote network. The network component that can send traffic to other networks is known as the default gateway. The router is responsible for directing traffic away from a local network. This happens when the sender host and the destination host are on different local networks. Using its routing database, the default gateway will be able to determine where to transmit the packet. The sender host does not need to be aware of any other destination for the packet save the router or default gateway. This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ Using the Default Gateway The router IP address for the network that the host is on is typically listed as the default gateway address in the routing table of a host. The host either manually configures the default gateway's IPv4 address or receives it from DHCP. When a host has a default gateway enabled, the host's routing table generates a default route, which is where a computer will send a packet when it wants to communicate with a distant network. Host Routing Tables On a Windows host, you can display the routing table using route print or netstat -r. Three sections will be displayed: Interface List – Lists the Media Access Control (MAC) address and assigned interface number of network interfaces on the host. IPv4 Route Table – Lists all known IPv4 routes. IPv6 Route Table – Lists all known IPv6 routes. Router Packet Forwarding Decision A router must consult its routing table to decide where to forward a packet when it is received and intended for a distant network. The routing table of a router includes: Directly connected routes - These routes originate from the IP address-configured active router interfaces. Remote routes - Routes from distant networks connected to other routers make up this category. Either manually or using a dynamic routing mechanism, they are configured. This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________  Default route - When a route is missing from the routing database, here is where the packet is sent. IPv4 Router Routing Table On a Cisco IOS router, the show ip route command is used to display the router’s IPv4 routing table. The routing table shows: Directly connected and remote routes How each route was learned Trustworthiness and rating of the route When the route was last updated Which interface is used to reach the destination A router examines an incoming packet’s header to determine the destination network. If there’s a match, the packet is forwarded using the specified information in the routing table. Directly Connected Routing Table Entries When a router interface is configured and activated, the following two routing table entries are created automatically: C – Identifies that the network is directly connected and the interface is configured with an IP address and activated. L – Identifies that it is a local interface. This is the IPv4 address of the interface on the router. This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ Understanding Remote Route Entries The D represents the Route Source which is how the network was learned by the router. D identifies the route as an EIGRP route or (Enhanced Interior Gateway Routing Protocol). 10.1.1.0/24 identifies the destination network. 90 is the administrative distance for the corresponding network –or the trustworthiness of the route. The lower the number, the more trustworthy it is. 2170112 – represents the metric or value assigned to reach the remote network. Lower values indicate preferred routes. 209.165.200.226 – Next-hop or IP address of the next router to forward the packet. 00:00:05 - Route Timestamp identifies when the router was last heard from. Serial/0/0/0 – Outgoing Interface Next-Hop Address A router will deliver a packet to the next hop address listed in its routing database when a packet with a destination network address arrives at the router. For instance, the R1 router in the picture on the left will deliver a packet to the next hop address of 209.165.200.226 if it receives a packet intended for a device on the 10.1.1.0/24 network. A packet for a network that is not listed in the routing table will be dropped by the router since there is no default gateway address defined in the routing table. This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ Skill-building Activities Packet Tracer Instruction: Look for the required file in the shared Packet tracer activity folder and open it with the Packet tracer. You will perform the Packet tracer activity listed below. The activity includes a step-by-step guide. After the activity is completed, your instructor will evaluate your work. Day11_Troubleshooting Default Gateway Issues.pka Check for Understanding Answer the following questions. Write the letter of the correct answer on the space provided. 1. What feature of the network layer in the OSI model enables packet transport for many forms of communications among numerous hosts? a) the de-encapsulation of headers from lower layers b) the selection of paths for and direct packets toward the destination c) the ability to operate without regard to the data that is carried in each packet d) the ability to manage the data transport between processes running on hosts 2. What are IP's two significant characteristics? (Select two.) a) does not need an end-to-end dedicated connection b) retransmits packets in the event of mistakes c) operates independently of network media. d) reassembles packets that have fallen out of order into the right order at the receiving end. e) Guarantees packet delivery 3. Which IPv4 header field is used to prevent a packet from traversing a network indefinitely? a) Time-to-Live b) Sequence Number c) Acknowledgment Number d) Differentiated Services. 4. What field in the IPv4 header identifies the upper layer protocol carried in the packet? a) Protocol b) Identification c) Version d) Differentiated Services 5. What is one advantage that the IPv6 simplified header offers over IPv4? a) smaller-sized header b) little requirement for processing checksums c) smaller-sized source and destination IP addresses d) efficient packet handling This document is the property of PHINMA EDUCATION  ITE 292: Networking 1 Module #11 Student Activity Sheet Name: _________________________________________________________ Class number: _______ Section: ____________ Schedule: __________________________________ Date: _______________ C. LESSON WRAP-UP FAQs 1. When a connectionless protocol is in use at a lower layer of the OSI model, how is missing data detected and retransmitted if necessary?  When connectionless protocols are in use at a lower layer of the OSI model, upper-level protocols may need to work together on the sending and receiving hosts to account for and retransmit lost data. In some cases, this is not necessary, because for some applications a certain amount of data loss is tolerable. 2. What routing table entry has a next hop address associated with a destination network?  A next hop IP address will be assigned to routing table entries for remote routes. The next hop IP address is the address of the next device's router interface that will be used to connect to the destination network. Because they do not need to go through another router to be reached, direct-connected and local routes have no next hop. Thinking about Learning Mark the place in the work tracker which is simply a visual to help you track how much you have accomplished and how much work there is left to do. This tracker will be part of your activity sheet. To develop habits on thinking about learning, answer the questions below about your learning experience. 1. How was the module able to help you learn? 2. What did you realize about the topic? This document is the property of PHINMA EDUCATION