1. CCNA1-1 Chapter 5 Week 6 OSI Network Layer

2. CCNA1-2 Chapter 5 Identify the role of the Network layer as it describes communication from one end device to another end device. Identify the role of the Network layer as it describes communication from one end device to another end device. Examine the most common Network layer protocol, Internet Protocol (IP), and its features for providing connectionless and best-effort service. Examine the most common Network layer protocol, Internet Protocol (IP), and its features for providing connectionless and best-effort service. Understand the principles used to guide the division, or grouping, of devices into networks. Understand the principles used to guide the division, or grouping, of devices into networks. Understand the hierarchical addressing of devices and how this allows communication between networks. Understand the hierarchical addressing of devices and how this allows communication between networks. Understand the fundamentals of routes, next-hop addresses, and packet forwarding to a destination network. Understand the fundamentals of routes, next-hop addresses, and packet forwarding to a destination network. Outcomes of this week

3. CCNA1-3 Chapter 5 OSI Network Layer Internet Protocol Version 4 (IPV4)

4. CCNA1-4 Chapter 5 Communication from Host to Host As we communicate… Devices use the Transport Layer to connect sessions… The network layer enables devices to reach each other… Routers find the best path…

5. CCNA1-5 Chapter 5 Communication from Host to Host Addresses packets with an IP Address.Addresses packets with an IP Address. Encapsulates the packet.Encapsulates the packet. Routes the packet to the destination.Routes the packet to the destination. Decapsulates the packet.Decapsulates the packet. Network Layer

6. CCNA1-6 Chapter 5 Network Layer Protocols We will be focusing on IPV4. We will be focusing on IPV4.

7. CCNA1-7 Chapter 5 IPV4: Example Network Layer Protocol Internet Protocol Version 4 (IPV4) is the most widely used version of IP. Internet Protocol Version 4 (IPV4) is the most widely used version of IP. Only Layer 3 protocol used on the Internet. Only Layer 3 protocol used on the Internet. Focus of this course. Focus of this course.

8. CCNA1-8 Chapter 5 IPV4: Example Network Layer Protocol Internet Protocol Version 6 (IPV6) is developed and slowly being implemented. Internet Protocol Version 6 (IPV6) is developed and slowly being implemented. Will eventually replace IPV4. Will eventually replace IPV4. Different characteristics than IPV4. Different characteristics than IPV4.

9. CCNA1-9 Chapter 5 IPV4: Example Network Layer Protocol Characteristics: Characteristics: ConnectionlessConnectionless “Best Effort” Delivery (Unreliable)“Best Effort” Delivery (Unreliable) Media IndependentMedia Independent

10. CCNA1-10 Chapter 5 Connectionless

11. CCNA1-11 Chapter 5 “Best Effort” Delivery (Unreliable) Unreliable means simply that IP does not have the capability to manage and recover from undelivered or corrupt packets. Unreliable means simply that IP does not have the capability to manage and recover from undelivered or corrupt packets. Since protocols at other layers can manage reliability, IP is allowed to function very efficiently at the Network Layer. Since protocols at other layers can manage reliability, IP is allowed to function very efficiently at the Network Layer.

12. CCNA1-12 Chapter 5 Media Independent Not concerned with the physical medium. Not concerned with the physical medium. Operates independent of the layers that handle the physical medium that carries the packet. Operates independent of the layers that handle the physical medium that carries the packet.

13. CCNA1-13 Chapter 5 Media Independent Is concerned with the size of the packet or Maximum Transmission Unit (MTU). Is concerned with the size of the packet or Maximum Transmission Unit (MTU). The MTU is established as part of the communication between the Data Link and Network Layers. The MTU is established as part of the communication between the Data Link and Network Layers. Fragmentation: Fragmentation: At times, an intermediary device (router) will need to split up a packet when forwarding it from one media to a media with a smaller MTU.At times, an intermediary device (router) will need to split up a packet when forwarding it from one media to a media with a smaller MTU.

14. CCNA1-14 Chapter 5 Media Independent Copper Ethernet: MTU = 1,518 bytes. Copper Ethernet: MTU = 1,518 bytes. Copper Serial: Frame Relay MTU = 512 bytes. Copper Serial: Frame Relay MTU = 512 bytes. Optical Fiber: ATM MTU = 17,966 bytes. Optical Fiber: ATM MTU = 17,966 bytes. Wireless: 802.11 MTU = 2272 bytes. Wireless: 802.11 MTU = 2272 bytes.

15. CCNA1-15 Chapter 5 Packaging the Transport Layer PDU In TCP/IP based networks, the Network Layer PDU is the IP Packet.

16. CCNA1-16 Chapter 5 IPV4 Packet Header 32 Bit binary value. Source of the packet 32 Bit binary value. Destination of the packet Maximum “hops” before undeliverable. 8 1-bit fields - Throughput Priority Upper Layer Protocol (TCP/UDP) Used in reconstruction of any fragments.

17. CCNA1-17 Chapter 5 OSI Network Layer Networks: Dividing Hosts into Groups

18. CCNA1-18 Chapter 5 Dividing Hosts into Groups As networks grow, they become too unwieldy to manage as a single entity. Often, the solution is to divide the large network into several more manageable sub-networks. The question is…..HOW?

19. CCNA1-19 Chapter 5 Dividing Hosts into Groups Should it be divided geographically?

20. CCNA1-20 Chapter 5 Dividing Hosts into Groups Should it be divided based on purpose?

21. CCNA1-21 Chapter 5 Dividing Hosts into Groups Should it be divided based on ownership?

22. CCNA1-22 Chapter 5 Why Separate Hosts into Networks? Performance Performance Security Security Address Management Address Management

23. CCNA1-23 Chapter 5 Performance Large numbers of hosts on a single network: Large numbers of hosts on a single network: Actual DataActual Data OverheadOverhead A big part of the overhead is broadcasts. A big part of the overhead is broadcasts. In this context, each network is called a broadcast domain. In this context, each network is called a broadcast domain. Switches forward broadcasts to each device connected to a switch port. Switches forward broadcasts to each device connected to a switch port. If we can reduce broadcast overhead, it would improve performance on the network. If we can reduce broadcast overhead, it would improve performance on the network. A

24. CCNA1-24 Chapter 5 Performance Routers block broadcasts unless specifically configured to forward them. Routers block broadcasts unless specifically configured to forward them. Replacing the switch in the diagram with a router, creates two separate IP sub-networks and two broadcast domains. Replacing the switch in the diagram with a router, creates two separate IP sub-networks and two broadcast domains. Broadcasts are now contained within each network. Broadcasts are now contained within each network. AB XX

25. CCNA1-25 Chapter 5 Security

26. CCNA1-26 Chapter 5 Address Management The role of the gateway….

27. CCNA1-27 Chapter 5 Hierarchical Addressing 12 3 4 IP Addresses are divided into a 2 level hierarchy – Network and Host.

28. CCNA1-28 Chapter 5 Dividing Networks from Networks The IP Version 4 Address contains elements that uniquely identify both the network and host. The IP Version 4 Address contains elements that uniquely identify both the network and host. An IP Address is like a telephone number: An IP Address is like a telephone number: 519-972-2727 519-972-2727 519 – Network Portion519 – Network Portion 972-2727 – Host Portion972-2727 – Host Portion 519 – Windsor area519 – Windsor area 972-2727 - St. Clair College972-2727 - St. Clair College

29. CCNA1-29 Chapter 5 Dividing Networks from Networks IP Version 4 addresses are 32 bits in length. Divided into four separate groups of 8 bits each – 4 Octets. Convert from binary to decimal – Dotted Decimal Notation.

30. CCNA1-30 Chapter 5 Dividing Networks from Networks An IP Version 4 address has two parts: An IP Version 4 address has two parts: Network numberNetwork number Host numberHost number The network portion of the address is the same for all hosts on the network.The network portion of the address is the same for all hosts on the network. Each device is identified by a unique host portion.Each device is identified by a unique host portion. This hierarchy means that routers only need to know the network portion – not the address of each individual host. This hierarchy means that routers only need to know the network portion – not the address of each individual host.

31. CCNA1-31 Chapter 5 Dividing Networks from Networks There is a direct relationship, bit for bit, between the IP Address and it's associated subnet mask. There is a direct relationship, bit for bit, between the IP Address and it's associated subnet mask. Any subnet mask bit that is a 1 means that the associated address bit belongs to the network number.Any subnet mask bit that is a 1 means that the associated address bit belongs to the network number. Any subnet mask bit that is a 0 means that the associated address bit belongs to the host number.Any subnet mask bit that is a 0 means that the associated address bit belongs to the host number. IP Address 192.168.1.2 Subnet Mask 255. 0 Binary IP Address 11000000101010000000000100000010 Binary Subnet Mask 11111111 00000000

32. CCNA1-32 Chapter 5 IP Addressing – The Subnet Mask There are two methods of expressing a subnet mask. There are two methods of expressing a subnet mask. The traditional method is to use the decimal value of the 1 bits that apply to the network.The traditional method is to use the decimal value of the 1 bits that apply to the network. 192.168.1.2 255.255.255.0192.168.1.2 255.255.255.0 This method is used for Classful Routing.This method is used for Classful Routing. The new method is known as IP Prefix or CIDR.The new method is known as IP Prefix or CIDR. Simply follow the IP address with a slash (/) and the number of bits that make up the network portion.Simply follow the IP address with a slash (/) and the number of bits that make up the network portion. The remainder of the 32 bits are for the host number.The remainder of the 32 bits are for the host number. 192.168.1.2 / 24192.168.1.2 / 24 This method indicates Classless Routing or Classless Interdomain Routing (CIDR).This method indicates Classless Routing or Classless Interdomain Routing (CIDR).

33. CCNA1-33 Chapter 5 IP Addressing – The Subnet Mask The network portion of the IP address assigned to all hosts on a network segment must be the same. The network portion of the IP address assigned to all hosts on a network segment must be the same. All hosts on a segment have the same subnet mask.All hosts on a segment have the same subnet mask.

34. CCNA1-34 Chapter 5 OSI Network Layer Routing: How Data Packets Are Handled

35. CCNA1-35 Chapter 5 Address Types Two address types: Two address types: MAC address:MAC address: Physical address of the hostPhysical address of the host Burned in to the NICBurned in to the NIC Layer 2 addressLayer 2 address Network Address:Network Address: Logical address of the hostLogical address of the host Assigned by network administratorAssigned by network administrator Layer 3 addressLayer 3 address

36. CCNA1-36 Chapter 5 Each Host Has Two Addresses Physical (MAC): Physical (MAC): The physical address uniquely identifies the host from all other hosts on all other networks at Layer 2.The physical address uniquely identifies the host from all other hosts on all other networks at Layer 2. This is the address that is absolutely necessary to get the information into the host. The IP address by itself won't accomplish that.This is the address that is absolutely necessary to get the information into the host. The IP address by itself won't accomplish that.

37. CCNA1-37 Chapter 5 Each Host Has Two Addresses Logical (IP): Logical (IP): The logical address uniquely identifies the host and the network to which it belongs at Layer 3.The logical address uniquely identifies the host and the network to which it belongs at Layer 3. Routers base their decisions on the NETWORK PORTION of the IP address when determining the best path for the packet.Routers base their decisions on the NETWORK PORTION of the IP address when determining the best path for the packet.

38. CCNA1-38 Chapter 5 Host X sends a packet to Host Y. Host X sends a packet to Host Y. A router generally relays a packet from one data link to another, using two basic functions: A router generally relays a packet from one data link to another, using two basic functions: a path determination function – Routinga path determination function – Routing a switching function – Packet Forwardinga switching function – Packet Forwarding Let’s go through all of the stages these routers use to route and switch this packet. Let’s go through all of the stages these routers use to route and switch this packet. IP Packets: Carrying Data End to End Remember: Two addresses are needed to move a packet from the source to the destination. MAC Address IP Address

39. CCNA1-39 Chapter 5 How does Host X know to forward the packet to Router A and not directly to Host Y? IP Packets: Carrying Data End to End Layer 2 Destination Layer 2 Source Layer 3 Destination Layer 3 Source A111H111192.168.4.10192.168.1.10 Host X begins by encapsulating a packet with Host Y’s IP address and Router A’s MAC address. Host X begins by encapsulating a packet with Host Y’s IP address and Router A’s MAC address. How does HOST X obtain Router A’s Layer 2 address? Host X determines that the destination is NOT on the same network. (More Later) The packet is forwarded to the default gateway. Queries the router for the router’s MAC address (more later).

40. CCNA1-40 Chapter 5 NOW what happens? IP Packets: Carrying Data End to End Layer 2 Destination Layer 2 Source Layer 3 Destination Layer 3 Source A111H111192.168.4.10192.168.1.10 Router A receives the packet on port fa0/0. Router A receives the packet on port fa0/0. Router A uses the destination IP address to search its routing table for network 192.168.4.0/24. It finds that it has a next hop address of 192.168.2.2 and an exit port of fa0/1.

41. CCNA1-41 Chapter 5 NOW what happens? IP Packets: Carrying Data End to End Layer 2 Destination Layer 2 Source Layer 3 Destination Layer 3 Source A111H111192.168.4.10192.168.1.10 Router A knows that the exit port is an Ethernet interface. Router A knows that the exit port is an Ethernet interface. Router A looks in a table of IP address to MAC address for all connected networks. If the network isn’t there, it queries Router B for it’s MAC address.

42. CCNA1-42 Chapter 5 IP Packets: Carrying Data End to End 192.168.1.10192.168.4.10H111A111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination Router A now has all of the information it needs to forward the packet. It knows that the destination MAC address is B111 and that the exit port is fa0/0. Router A now has all of the information it needs to forward the packet. It knows that the destination MAC address is B111 and that the exit port is fa0/0. Router A now re-encapsulates the frame, changing the Layer 2 addresses and forwards (switches) the frame out port fa0/1. Router A now re-encapsulates the frame, changing the Layer 2 addresses and forwards (switches) the frame out port fa0/1. 192.168.1.10192.168.4.10A222B111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination

43. CCNA1-43 Chapter 5 192.168.1.10192.168.4.10A222B111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End Notice that the Layer 3 addresses in the packet DID NOT change! Notice that the Layer 3 addresses in the packet DID NOT change! Also notice that the routing table was used to find: Also notice that the routing table was used to find: The next hop Layer 3 addressThe next hop Layer 3 address The next hop Layer 2 addressThe next hop Layer 2 address The exit port to use to forward the frame.The exit port to use to forward the frame.

44. CCNA1-44 Chapter 5 192.168.1.10192.168.4.10A222B111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End Router B receives the packet. Router B receives the packet. NOW what happens? Router B uses the destination IP address to search its routing table for network 192.168.4.0/24. It finds that it has a next hop address of 192.168.3.2 and an exit port of s0/1 – a serial interface.

45. CCNA1-45 Chapter 5 192.168.1.10192.168.4.10A222B111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End Router B knows that the exit port is a serial interface. Router B knows that the exit port is a serial interface. NOW what happens? Since the exit interface is a serial interface, NOT an Ethernet interface, Router B does not need the Layer 2 address for the next hop. Remember, serial interfaces are like a pipe – one way in and one way out.

46. CCNA1-46 Chapter 5 192.168.1.10192.168.4.10A222B111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End When the interface is a point-to- point serial connection, the routing table process does not even look at the next-hop IP address. When the interface is a point-to- point serial connection, the routing table process does not even look at the next-hop IP address. Router B now encapsulates the IP packet into the proper data link frame, using the proper serial encapsulation (HDLC, PPP, etc.). Router B now encapsulates the IP packet into the proper data link frame, using the proper serial encapsulation (HDLC, PPP, etc.).

47. CCNA1-47 Chapter 5 192.168.1.10192.168.4.10A222B111 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination 192.168.1.10192.168.4.10B222FFFF Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End The destination Layer 2 address is set to a broadcast since there is only one other end to the pipe. The source Layer 2 address is set to the exit port of Router B – the source of the frame. Finally, the frame is forwarded (switched) out port s0/1 on Router B.

48. CCNA1-48 Chapter 5 192.168.1.10192.168.4.10B222FFFF Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End Router C receives the frame on the serial interface - port s0/1 Router C receives the frame on the serial interface - port s0/1 NOW what happens? Router C uses the destination IP address to search its routing table for network 192.168.4.0/24. It finds that the network is a directly connected network with an exit interface of fa0/0.

49. CCNA1-49 Chapter 5 192.168.1.10192.168.4.10B222FFFF Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End Router C realizes that this destination IP address is on the same network as one of its interfaces and it can send the packet directly to the destination and not another router. Router C realizes that this destination IP address is on the same network as one of its interfaces and it can send the packet directly to the destination and not another router. Since the exit interface is on an directly connected Ethernet network, Router C must obtain the destination’s MAC address. Since the exit interface is on an directly connected Ethernet network, Router C must obtain the destination’s MAC address.

50. CCNA1-50 Chapter 5 192.168.1.10192.168.4.10B222FFFF Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End Router C looks in a table of IP address to MAC address for all connected networks. Router C looks in a table of IP address to MAC address for all connected networks. If the entry was not in the table, Router C would need to send a query out fa0/0 that says, “What is the MAC address for this IP address?” If the entry was not in the table, Router C would need to send a query out fa0/0 that says, “What is the MAC address for this IP address?” Host Y would send back a reply that says, “This is the MAC address that matches the IP Address you sent.” Host Y would send back a reply that says, “This is the MAC address that matches the IP Address you sent.”

51. CCNA1-51 Chapter 5 192.168.1.10192.168.4.10B222FFFF Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination IP Packets: Carrying Data End to End 192.168.1.10192.168.4.10C222H222 Layer 3 Source Layer 3 Destination Layer 2 Source Layer 2 Destination Router C encapsulates the Ethernet frame and uses the destination MAC address of Host Y. The source Layer 2 address becomes the MAC address of the router’s fa0/0 port. The frame is forwarded (switched) out port fa0/0 to the destination host – Host Y.

52. CCNA1-52 Chapter 5 IP Packets: Carrying Data End to End Step Layer 2 Destination Layer 2 Source Layer 3 Destination Layer 3 Source Host X to Router A A111H111192.168.4.10192.168.1.10 Router A to Router B B111A222192.168.4.10192.168.1.10 Router B to Router C FFFFB222192.168.4.10192.168.1.10 Router C to Host Y H222C222192.168.4.10192.168.1.10 NOTICE THAT THE SOURCE AND DESTINATION IP ADDRESSES REMAIN UNCHANGED!!!

53. CCNA1-53 Chapter 5 Gateway: The Way Out of the Network Default Gateway is defined to all hosts on the network. Default Gateway is defined to all hosts on the network. Gateway address is the address of the router interface. Gateway address is the address of the router interface. Network portion must be on the same network as all of the hosts.Network portion must be on the same network as all of the hosts.

54. CCNA1-54 Chapter 5 Gateway: The Way Out of the Network Additionally, no packet can be forwarded without a route. Additionally, no packet can be forwarded without a route. A router makes a forwarding decision for each packet that arrives at the gateway interface. A router makes a forwarding decision for each packet that arrives at the gateway interface. The destination may be one or more hops away. The destination may be one or more hops away.

55. CCNA1-55 Chapter 5 Route: A Path to a Network The routing table stores information about directly connected and remote networks. The routing table stores information about directly connected and remote networks. Remote networks are networks not directly connected to the router (manual configuration or learned dynamically). Remote networks are networks not directly connected to the router (manual configuration or learned dynamically). Destination Network Next HopMetric

56. CCNA1-56 Chapter 5 Host Routing Table Hosts also require a local routing table so that Network layer packets are directed to the correct destination network. Hosts also require a local routing table so that Network layer packets are directed to the correct destination network. Unlike a router, the host routing table usually contains only the host’s address and the default gateway. Unlike a router, the host routing table usually contains only the host’s address and the default gateway.

57. CCNA1-57 Chapter 5 Destination Network - Routing Table Entries The hierarchical nature of Layer 3 addressing means that… The hierarchical nature of Layer 3 addressing means that… One route entry could refer to a large general network.One route entry could refer to a large general network. Another entry could refer to a subnet of that same network.Another entry could refer to a subnet of that same network. When forwarding a packet, the router will select the most specific route.When forwarding a packet, the router will select the most specific route.

58. CCNA1-58 Chapter 5 Destination Network - Routing Table Entries The default route in a routing table performs much the same function as a default gateway in a PC. The default route in a routing table performs much the same function as a default gateway in a PC. If a route for a packet cannot be found in the routing table, and a default route is present, that route will be used to forward the packet.If a route for a packet cannot be found in the routing table, and a default route is present, that route will be used to forward the packet.

59. CCNA1-59 Chapter 5 Destination Network - Routing Table Entries If a packet arrives destined for 207.23.124.56, the router would check the table in the following order: If a packet arrives destined for 207.23.124.56, the router would check the table in the following order: 10.1.1.010.1.1.0 10.1.0.010.1.0.0 10.0.0.010.0.0.0 0.0.0.0 0.0.0.0 Since the route doesn’t exist and a default route is configured, the packet would be forwarded to the next hop. Destination Network Next HopMetric

60. CCNA1-60 Chapter 5 Packet Forwarding: Route Found L2IPTCPDATAL2 IPTCPDATA Data for Host 10.1.2.2 / 24 Network 10.1.1.0 Network 10.1.2.0 L2IPTCPDATAL2 IP Address 10.1.2.2 is on network 10.1.2.0

61. CCNA1-61 Chapter 5 Packet Forwarding: Default Route L2IPTCPDATAL2 IPTCPDATA Data for Host 207.1.1.1 / 24 Network 10.1.1.0 Network 10.1.2.0 L2IPTCPDATAL2 IP Address 207.1.1.1 is on network 207.1.1.0

62. CCNA1-62 Chapter 5 Packet Forwarding: Route Not Found L2IPTCPDATAL2 IPTCPDATA Data for Host 207.1.1.1 / 24 Network 10.1.1.0 Network 10.1.2.0 IP Address 207.1.1.1 is on network 207.1.1.0 ?

63. CCNA1-63 Chapter 5 OSI Network Layer Routing Processes: How Routes Are Learned

64. CCNA1-64 Chapter 5 Routing Processes: How Routes Are Learned Routing requires that every hop, or router, along the path to a packet's destination have a route to forward the packet. Routing requires that every hop, or router, along the path to a packet's destination have a route to forward the packet. The routing table contains the information to make packet forwarding decisions. The routing table contains the information to make packet forwarding decisions. Information is learned in two ways: Information is learned in two ways: Manual configuration of the information (Static)Manual configuration of the information (Static) Information received from another router (Dynamic)Information received from another router (Dynamic)

65. CCNA1-65 Chapter 5 Static Routing Manually configured. Manually configured. Must know network structure. Must know network structure. Every router between each source and destination must have routes. Every router between each source and destination must have routes. Changes to the topology require static route changes. Changes to the topology require static route changes.

66. CCNA1-66 Chapter 5 Dynamic Routing Routing information is exchanged among the routers using a routing protocol. Routing information is exchanged among the routers using a routing protocol. Route always up to date with little administration but creates overhead. Route always up to date with little administration but creates overhead.

67. CCNA1-67 Chapter 5 Routing Protocols Routing Information Protocol (RIP) Routing Information Protocol (RIP) Enhanced Interior Gateway Protocol (EIGRP) Enhanced Interior Gateway Protocol (EIGRP) Open Shortest Path First (OSPF) Open Shortest Path First (OSPF)