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Any Questions?

Any Questions?. Chapter 15-Troubleshooting IP Routing. IP Troubleshooting Tips and Tools A Troubleshooting Scenario. Do I know this?. Go through the Quiz- 5 minutes.

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Any Questions?

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  1. Any Questions?

  2. Chapter 15-Troubleshooting IP Routing • IP Troubleshooting Tips and Tools • A Troubleshooting Scenario

  3. Do I know this? Go through the Quiz- 5 minutes

  4. 1. An internetwork diagram shows a router, R1, with the ip subnet-zero command configured. The engineer has typed several configuration commands into a word processor for later pasting into the router’s configuration. Which of the following IP addresses could not be assigned to the router’s Fa0/0 interface? a. 172.16.0.200 255.255.255.128 b. 172.16.0.200 255.255.255.0 c. 225.1.1.1 255.255.255.0 d. 10.43.53.63 255.255.255.192

  5. 2. Which of the following is a useful command on some Microsoft OSs for discovering a host’s current IP address and mask? a. tracert b. ipconfig /all c. arp –a d. ipconfig /displaydns

  6. 3. Examine the following command output. If the user typed the resume command, what would happen? R1#show sessions Conn Host Address Byte Idle Conn Name 1 Fred 10.1.1.1 0 0 Fred * 2 Barney 10.1.2.1 0 0 Barney a. The command would be rejected, and the R1 CLI command prompt would be displayed again. b. The CLI user would be connected to a suspended Telnet connection to the router with IP address 10.1.1.1. c. The CLI user would be connected to a suspended Telnet connection to the router with IP address 10.1.2.1. d. The result cannot be accurately predicted from the information shown.

  7. 4. If PC3 were added to the LAN on the left, with IP address 10.1.1.130/25, default gateway 10.1.1.1, which of the following would be true? a. If PC1 issued a ping 10.1.1.130 command, PC1 would use ARP to learn PC3’s MAC address. b. If PC3 issued a ping 10.1.1.10 command, PC3 would ARP trying to learn PC1’s MAC address. c. If PC1 issued a ping 10.1.13.1 command, PC1 would ARP trying to learn the MAC address of 10.1.13.1. d. If R1 issued a ping 10.1.1.130 command, R1 would ARP trying to learn the MAC address of 10.1.1.130.

  8. 5. A new network engineer is trying to troubleshoot a problem for the user of PC1. Which of the following tasks and results would most likely point to a Layer 1 or 2 Ethernet problem on the LAN on the left side of the figure? a. A ping 10.1.1.1 command on PC1 did not succeed. b. A ping 10.1.13.3 command from PC1 succeeded, but a ping 172.16.2.4 did not. c. A ping 10.1.1.1 command from PC1 succeeded, but a ping 10.1.13.1 did not. d. A ping 10.1.1.10 command from PC1 succeeded.

  9. 6. The PC2 user issues the tracert 10.1.1.10 command. Which of the following IP addresses could be shown in the command output? a. 10.1.1.10 b. 10.1.1.1 c. 10.1.13.1 d. 10.1.13.3 e. 172.16.2.4

  10. 7. All the devices in the figure just booted, and none of the devices has yet sent any data frames. Both PCs use statically configured IP addresses. Then PC1 successfully pings PC2. Which of the following ARP table entries would you expect to see? a. An entry on PC1’s ARP cache for IP address 172.16.2.7 b. An entry on PC1’s ARP cache for IP address 10.1.1.1 c. An entry on R1’s ARP cache for IP address 10.1.1.10 d. An entry on R1’s ARP cache for IP address 172.16.2.7

  11. 8. All the devices in the figure just booted, and none of the devices has yet sent any data frames. Both PCs use statically configured IP addresses. Then PC1 successfully pings PC2. Which of the following ARP requests would you expect to occur? a. PC1 would send an ARP broadcast looking for R1’s MAC address of the interface with IP address 10.1.1.1. b. PC2 would send an ARP broadcast looking for R2’s MAC address of the interface with IP address 172.16.2.4. c. R1 would send an ARP broadcast looking for PC1’s MAC address. d. R2 would send an ARP broadcast looking for PC2’s MAC address. e. PC1 would send an ARP broadcast looking for PC2’s MAC address.

  12. 9. PC1 is successfully pinging PC2 in the figure. Which of the following is true about the packets? a. The frame going left-to-right, as it crosses the left-side LAN, has a destination MAC address of R1’s MAC address. b. The frame going left-to-right, as it crosses the right-side LAN, has a destination MAC address of R2’s MAC address. c. The frame going left-to-right, as it crosses the serial link, has a destination IP address of PC2’s IP address. d. The frame going right-to-left, as it crosses the left-side LAN, has a source MAC address of PC2’s MAC address. e. The frame going right-to-left, as it crosses the right-side LAN, has a source MAC address of PC2’s MAC address. f. The frame going right-to-left, as it crosses the serial link, has a source MAC address of R2’s MAC address.

  13. Any Questions?

  14. IP Addressing Review • Reserved Addresses • 0 (because network 0.0.0.0 is always reserved) • 127 (because network 127.0.0.0 is always reserved) • 224–239 (all Class D multicast IP addresses) • 240–255 (all Class E experimental IP addresses) • Reserved on every Network-cannot give to a host • Subnet address (all 0 in the host portion of address) • Subnet Broadcast address (all 1 in the host portion) • Reserved Subnets • Subnet 0 • Broadcast subnet Pg 475-476

  15. When are subnets reserved Pg 476

  16. One subnet/mask for each LAN • Each LAN (each network connected to a router interface) will have its own network (or subnet) • You might have to discover them by using show commands Pg 476-477

  17. IP Addressing Tips 1. Check the mask used on each device in the same LAN; if different, then the devices cannot have the same view of the range of addresses in the subnet. 2. On point-to-point WAN links, check the IP addresses and masks on both ends of the link, and confirm that the two IP addresses are in the same subnet. 3. When checking to confirm that hosts are in the same subnet, do not just examine the subnet number. Also check the subnet mask, and the implied range of IP addresses. 4. Be ready to use the commands summarized in Table 15-4 to quickly find the IP addresses, masks, and subnet numbers. Pg 478

  18. Host Networking • Steps a host takes when routing Routing: If the packet’s destination is on the same subnet, send the packet directly; if not, send the packet to the default gateway. Address assignment: Before sending any packets, the host may use DHCP client services to learn its IP address, mask, default gateway, and DNS IP addresses. The host could also be statically configured with these same details. Name resolution: When the user directly or indirectly references a host name, the host typically uses DNS name resolution requests to ask a DNS to identify that host’s IP address unless the host already has that information in its name cache. IP-to-MAC resolution: The host uses ARP requests to find the other host’s MAC address, or the default gateway’s IP address, unless the information is already in the host’s ARP cache. Pg 478

  19. Troubleshooting Host Routing Problems • If a ping between hosts on a LAN doesn’t work • IP/Mask configuration • Check configs • Bad ethernet • Check interfaces Pg 482

  20. Troubleshooting Host Routing Problems • If you can ping your own subnet, but not others • Gateway configuration is off-IP or mask mismatch • Layer 1 or 2 errors • Perhaps one side of router works, but other is disabled Pg 482

  21. Finding a matching route • When a particular destination IP address matches more than one route in a router’s routing table, the router uses the most specific route—in other words, the route with the longest prefix length. • Although the router uses binary math to compare the destination IP address to the routing table entries, you can simply compare the destination IP address to each subnet in the routing table. If a subnet’s implied address range includes the packet’s destination address, the route matches the packet’s destination. • If the question includes a simulator, you can easily find the matche route by using the show ip route address command, which lists the route matched for the IP address listed in the command. Pg 483

  22. Troubleshooting commands • Sh ip arp • Traceroute • Telnet and Suspend • CTRL-SHIFT-6 x

  23. Troubleshooting Scenario • Go through it-

  24. Any Questions?

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