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Network layer

Network layer. Chapter 6 Intro to Routing & Switching. objectives. Upon completion of this chapter, you should be able to: Describe the purpose of the network layer Explain why IPv4 uses other layers for reliability Explain how host devices use routing tables to direct packets

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Network layer

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  1. Network layer Chapter 6 Intro to Routing & Switching

  2. objectives • Upon completion of this chapter, you should be able to: • Describe the purpose of the network layer • Explain why IPv4 uses other layers for reliability • Explain how host devices use routing tables to direct packets • Compare host and router routing tables • Describe components of a router • Describe the boot-up process of a Cisco router • Configure a Cisco router and interfaces • Configure a default gateway

  3. 6.1.1 The network layer

  4. Network layer

  5. 6.1.2 All about ip

  6. ip • Low overhead • Delivers packet to destination only • Does NOT track or manage flow • Other layers handle that • Connectionless • Doesn’t need a connection established w/ dest. • Best effort delivery • Unreliable, no guarantee (other layers) • Media independent • Doesn’t matter which type of cable being used

  7. Media independent • Doesn’t matter what cables/media it travels over • What layer handles the prep for media?

  8. ACTIVITY • 6.1.2.6 • Read each IP characteristic & decide if it describes connectionless, best effort, or media independent.

  9. Review- 3Q • IP is described as connectionless, or connection-oriented? • Connectionless • When using IP, what protocol would be used to acknowledge delivery of packets and retransmission of missing ones? • TCP • What layer does TCP operate at? • Transport

  10. 6.1.3 Ipv4 packet

  11. ipV4 packet • Includes Header & Payload • Header includes: • Source & destination IP • DS (Differentiated Services) • Defines the priority of each packet • Protocol • TCP/UDP • TTL (Time-to-Live) • Hops until dropped

  12. Sample ipv4 header Version, IP’s DS, Total Length, Flags, TTL

  13. review • Which field in the IPv4 header… • Tells the priority of a packet? • DS • Helps with fragmented packets when split to not exceed the MTU on media? • Flags • Name a connectionless layer 3 protocol that is popular & in use today? • IP • What helps IP with guaranteed delivery? • TCP

  14. 6.1.4 Ipv6 packet

  15. What’s wrong with ipv4? • Running out of addresses • Routing tables growing • Lack of end to end connectivity • NAT is normally used • NAT allows certain private IP addresses to be used within a network and not shared with the outside world • The internal private IP gets translated to a public one to send data across Internet

  16. IPv4 to IPv6 • 32-bit addresses • 4 billion available • Many header fields • Must use NAT • To conserve addresses • 128-bit addresses • 340 undecillion avail. • Less header fields • Better packet handling • No need for NAT • A lot of IPv6 addresses IPv4 IPv6

  17. Ipv6 header & IPv4 header

  18. Sample ipv6 header Version, Payload Length, Hop Limit, IPv6 addresses

  19. activity • Handout to compare IPv4 & 6 headers • 6.1.4.6 • Read each IPv6 header description & click which field it belongs to.

  20. review • Explain NAT. • Private internal IP addresses. Can’t be seen outside network. Translate to a public IP for the entire internal network. • Why is NAT not needed with IPv6? • A ton of addresses! • What field in an IPv6 header… • Has routers use the same path for real-time packets? • Flow label • Is like the DS field for priority? • Traffic Class

  21. review • Review the picture. • What kind of IP is being used? • IPv4 • How many hops from PC1 to PC33? • 3

  22. 6.2.1 How a host routes

  23. Host ready to send • Itself (loopback) • 127.0.0.1 • Local • Shares same network address • Remote • On a different network

  24. Host ipv4 routing table • PC has a “mini” routing table

  25. activity • 6.2.1.7 • Identify the parts of a host routing table

  26. review • How does a PC know where to send packets? • It has its own routing table • What 2 commands on a PC will view the routing table? • Netstat –r or route print

  27. review

  28. 6.2.2 Router routing table

  29. How to route the packet • After packet reaches DG (router), it looks at the routing table to see where to send it • What’s in the table? • Directly connected routes • Remote routes

  30. What would it know?

  31. Routing table • Show ip route • Stored in RAM • How it was learned • When it was updated • Which interface to use to get to that network

  32. Parts of routing table

  33. ROUTING TABLE- OTHER NETWORKS

  34. 192.168.10.0/24 10.1.1.0/24 .10 .10 G0/0 .1 209.165.200.224 /30 PC1 .1 .226 .225 S0/0/0 R1 R2 .1 G0/1 .1 .10 .10 PC2 10.1.2.0/24 192.168.11.0/24 R1#show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.1.1.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 D 10.1.2.0/24 [90/2170112] via 209.165.200.226, 00:00:05, Serial0/0/0 192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.10.0/24 is directly connected, GigabitEthernet0/0 L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks C 192.168.11.0/24 is directly connected, GigabitEthernet0/1 L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks C 209.165.200.224/30 is directly connected, Serial0/0/0 L 209.165.200.225/32 is directly connected, Serial0/0/0 R1#

  35. activity • 6.2.2.7 • Identify the elements of a routing table • Lab 6.2.2.8 • Discover your PC’s routing table

  36. review • A packet comes into the interface of a router. Which address does it check? • Destination IP • What does it then use that address to look at? • Routing table • What happens if a match is found for the destination network? • It sends it out that port towards that destination

  37. review • What command displays the routing table on a router? • Show ip route • Where is the routing table stored? • RAM • What would happen if a destination network was not in the routing table and there was no default route configured? • Packet is dropped

  38. 6.3.1 Anatomy of a router

  39. The router is a computer • OS • RAM • CPU • ROM

  40. Router memory

  41. Router interfaces WAN Serial Ports in slot LAN interfaces LAN Interfaces in slot Console Port RJ45 AUX Port RJ45

  42. activity • 6.3.1.8 • Match the router interface or function with its description • Lab 6.3.1.9 • Explore the router externally & using show commands • Lab 6.3.1.10 • Determine connectivity options on a router

  43. Review- 5Q • Where is the IOS stored? • Flash • Where is the running-config at? • RAM • Where is the startup-config stored? • NVRAM • Where is the limited IOS at? • ROM • Where is the routing table stored? • RAM

  44. Review- 4Q • Based on the last 5 questions, which ones will get “lost” if you lose power to the router & why? • Running-config & routing table because they are in RAM • Which ports on the router will allow out-of-band management? • Console & AUX • If you want to gain access to router configuration remotely through Telnet or SSH, which interfaces would you be “connecting” to? • Ethernet/LAN or Serial/WAN • What 2 things get copied into RAM upon a normal boot? • IOS & startup-config

  45. 6.3.2 Router boot-up

  46. Boot summary • Similar to PC booting • POST • IOS in flash memory & loads into RAM • Startup-config loads into RAM • Becomes running-config • Changes made to config happen in RAM/running-config • MUST SAVE THEM!

  47. Step 1 • POST tests hardware (CPU, Memory) • ROM: Bootstrap • Boot Image • Begins search for IOS

  48. Step 2 • Locate & load IOS into RAM • Usually in Flash (default) or TFTP Server

  49. Step 3 • Configuration File or Setup • NVRAM (1st), TFTP Server (2nd), Console (3rd) • If found, copies into RAM • Becomes the running-config • If not found, enters Setup Mode

  50. Verify & troubleshoot • Show version • IOS version • Version of bootstrap • Location & name of IOS • CPU & RAM • Interfaces • Amount of NVRAM & Flash • Config-register • 0x2102

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