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Any Questions?. Chapter 4 IP Routing: Static and Connected Routes. IP Routing and Addressing Routes to Directly Connected Subnets Static Routes. Do I know this?. Go through the Quiz- 5 minutes.

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  1. Any Questions?

  2. Chapter 4 IP Routing: Static and Connected Routes • IP Routing and Addressing • Routes to Directly Connected Subnets • Static Routes

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

  4. 1. A PC user turns on her computer, and as soon as the computer is up and working, she opens a web browser to browse http://www.ciscopress.com. Which protocol(s) would definitely not be used by the PC during this process? a. DHCP b. DNS c. ARP d. ICMP

  5. 1. A PC user turns on her computer, and as soon as the computer is up and working, she opens a web browser to browse http://www.ciscopress.com. Which protocol(s) would definitely not be used by the PC during this process? a. DHCP b. DNS c. ARP d. ICMP Answer D

  6. 2. A PC user turns on her computer, and as soon as the computer is up and working, she opens a command prompt. From there, she issues the ping 2.2.2.2 command, and the ping shows 100 percent success. The PC’s IP address is 1.1.1.1 with mask 255.255.255.0. Which of the following settings would be required on the PC to support the successful ping? a. The IP address of a DNS server b. The IP address of a default gateway c. The IP address of an ARP server d. The IP address of a DHCP server

  7. 2. A PC user turns on her computer, and as soon as the computer is up and working, she opens a command prompt. From there, she issues the ping 2.2.2.2 command, and the ping shows 100 percent success. The PC’s IP address is 1.1.1.1 with mask 255.255.255.0. Which of the following settings would be required on the PC to support the successful ping? a. The IP address of a DNS server b. The IP address of a default gateway c. The IP address of an ARP server d. The IP address of a DHCP server Answer B

  8. 3. Router 1 has a Fast Ethernet interface 0/0 with IP address 10.1.1.1. The interface is connected to a switch. This connection is then migrated to use 802.1Q trunking. Which of the following commands could be part of a valid configuration for Router 1’s Fa0/0 interface? a. interface fastethernet 0/0.4 b. dot1q enable c. dot1q enable 4 d. trunking enable e. trunking enable 4 f. encapsulation dot1q

  9. 3. Router 1 has a Fast Ethernet interface 0/0 with IP address 10.1.1.1. The interface is connected to a switch. This connection is then migrated to use 802.1Q trunking. Which of the following commands could be part of a valid configuration for Router 1’s Fa0/0 interface? a. interface fastethernet 0/0.4 b. dot1q enable c. dot1q enable 4 d. trunking enable e. trunking enable 4 f. encapsulation dot1q Answer A and F

  10. 4. A router is configured with the no ip subnet-zero global configuration command. Which of the following interface subcommands would not be accepted by this router? a. ip address 10.1.1.1 255.255.255.0 b. ip address 10.0.0.129 255.255.255.128 c. ip address 10.1.2.2 255.254.0.0 d. ip address 10.0.0.5 255.255.255.252 Answer: C

  11. 4. A router is configured with the no ip subnet-zero global configuration command. Which of the following interface subcommands would not be accepted by this router? a. ip address 10.1.1.1 255.255.255.0 b. ip address 10.0.0.129 255.255.255.128 c. ip address 10.1.2.2 255.254.0.0 d. ip address 10.0.0.5 255.255.255.252 Answer: C

  12. 5. Which of the following must be true before IOS lists a route as “S” in the output of a show ip route command? a. The IP address must be configured on an interface. b. The router must receive a routing update from a neighboring router. c. The ip route command must be added to the configuration. d. The ip address command must use the special keyword. e. The interface must be up and up.

  13. 5. Which of the following must be true before IOS lists a route as “S” in the output of a show ip route command? a. The IP address must be configured on an interface. b. The router must receive a routing update from a neighboring router. c. The ip route command must be added to the configuration. d. The ip address command must use the special keyword. e. The interface must be up and up. Answer: C

  14. 6. Which of the following commands correctly configures a static route? a. ip route 10.1.3.0 255.255.255.0 10.1.130.253 b. ip route 10.1.3.0 serial 0 c. ip route 10.1.3.0 /24 10.1.130.253 d. ip route 10.1.3.0 /24 serial 0

  15. 6. Which of the following commands correctly configures a static route? a. ip route 10.1.3.0 255.255.255.0 10.1.130.253 b. ip route 10.1.3.0 serial 0 c. ip route 10.1.3.0 /24 10.1.130.253 d. ip route 10.1.3.0 /24 serial 0 Answer: A

  16. 7. Which of the following is affected by whether a router is performing classful or classless routing? a. When to use a default route b. When to use masks in routing updates c. When to convert a packet’s destination IP address to a network number d. When to perform queuing based on the classification of a packet into a particular queue

  17. 7. Which of the following is affected by whether a router is performing classful or classless routing? a. When to use a default route b. When to use masks in routing updates c. When to convert a packet’s destination IP address to a network number d. When to perform queuing based on the classification of a packet into a particular queue Answer: A

  18. 8. A router has been configured with the ip classless global configuration command. The router receives a packet destined to IP address 168.13.4.1. The following text lists the contents of the router’s routing table. Which of the following is true about how this router forwards the packet? Gateway of last resort is 168.13.1.101 to network 0.0.0.0 168.13.0.0/24 is subnetted, 2 subnets C 168.13.1.0 is directly connected, FastEthernet0/0 R 168.13.3.0 [120/1] via 168.13.100.3, 00:00:05, Serial0.1 a. It is forwarded to 168.13.100.3. b. It is forwarded to 168.13.1.101. c. It is forwarded out interface Fa0/0, directly to the destination host. d. The router discards the packet.

  19. 8. A router has been configured with the ip classless global configuration command. The router receives a packet destined to IP address 168.13.4.1. The following text lists the contents of the router’s routing table. Which of the following is true about how this router forwards the packet? Gateway of last resort is 168.13.1.101 to network 0.0.0.0 168.13.0.0/24 is subnetted, 2 subnets C 168.13.1.0 is directly connected, FastEthernet0/0 R 168.13.3.0 [120/1] via 168.13.100.3, 00:00:05, Serial0.1 a. It is forwarded to 168.13.100.3. b. It is forwarded to 168.13.1.101. c. It is forwarded out interface Fa0/0, directly to the destination host. d. The router discards the packet. Answer: B

  20. Any Questions?

  21. IP Routing HOST Logic • 1. When sending a packet, compare the destination IP address of the packet to the sending host’s perception of the range of addresses in the connected subnet, based on the host’s IP address and subnet mask. • a. If the destination is in the same subnet as the host, send the packet directly to the destination host. Address Resolution Protocol (ARP) is needed to find the destination host’s MAC address. • b. If the destination is not in the same subnet as the host, send the packet directly to the host’s default gateway (default router). ARP is needed to find the default gateway’s MAC address. Pg 162

  22. IP Routing ROUTER logic 1. For each received frame, use the data-link trailer frame check sequence (FCS) field to ensure that the frame had no errors; if errors occurred, discard the frame (and do not continue to the next step). 2. Check the frame’s destination data link layer address, and process only if addressed to this router or to a broadcast/multicast address. 3. Discard the incoming frame’s old data-link header and trailer, leaving the IP packet. 4. Compare the packet’s destination IP address to the routing table, and find the route that matches the destination address. This route identifies the outgoing interface of the router, and possibly the next-hop router. 5. Determine the destination data-link address used for forwarding packets to the next router or destination host (as directed in the routing table). 6. Encapsulate the IP packet inside a new data-link header and trailer, appropriate for the outgoing interface, and forward the frame out that interface. Pg 163

  23. IP Routing Example Pg 164

  24. WAN Routing Process Pg 166

  25. IP Addressing and Subnetting • For each subnet, recognize the following: • Subnetwork Address • Range of Hosts • Subnetwork Broadcast Address Pg 166

  26. MAJOR IP addressing concepts ■ Unicast IP addresses are IP addresses that can be assigned to an individual interface for sending and receiving packets. ■ Each unicast IP address resides in a particular Class A, B, or C network, called a classful IP network. ■ If subnetting is used, which is almost always true in real life, each unicast IP address also resides in a specific subset of the classful network called a subnet. ■ The subnet mask, written in either dotted decimal form (for example, 255.255.255.0) or prefix notation form (for example, /24), identifies the structure of unicast IP addresses and allows devices and people to derive the subnet number, range of addresses, and broadcast address for a subnet. ■ Devices in the same subnet should all use the same subnet mask; otherwise, they have different opinions about the range of addresses in the subnet, which can break the IP routing process. Pg 167

  27. MAJOR IP addressing concepts ■ Devices in a single VLAN should be in the same single IP subnet. ■ Devices in different VLANs should be in different IP subnets. ■ To forward packets between subnets, a device that performs routing must be used. In this book, only routers are shown, but multilayer switches—switches that also perform routing functions—can also be used. ■ Point-to-point serial links use a different subnet than the LAN subnets, but these subnets only require two IP addresses, one for each router interface on either end of the link. ■ Hosts separated by a router must be in separate subnets. Pg 167

  28. Subnets in action Pg 168

  29. Subnetting Review • CD-only Appendix D, “Subnetting Practice” • CD-only Appendix E, “Subnetting Reference Pages” • CD-only Appendix H, “ICND1 Chapter 12: IP Addressing and Subnetting” • Subnetting videos Pg 168

  30. IP Forwarding and most specific route • Often their might be overlapping routes in a routers table: • The use of autosummary • Manual route summarization • The use of static routes • Incorrectly designed subnetting so that subnets overlap their address ranges Pg 169

  31. Overlapping Routes • 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. Pg 169

  32. Multiple Routes in Action R1#show ip route rip 172.16.0.0/16 is variably subnetted, 5 subnets, 4 masks R 172.16.1.1/32 [120/1] via 172.16.25.2, 00:00:04, Serial0/1/1 R 172.16.1.0/24 [120/2] via 172.16.25.129, 00:00:09, Serial0/1/0 R 172.16.0.0/22 [120/1] via 172.16.25.2, 00:00:04, Serial0/1/1 R 172.16.0.0/16 [120/2] via 172.16.25.129, 00:00:09, Serial0/1/0 R 0.0.0.0/0 [120/3] via 172.16.25.129, 00:00:09, Serial0/1/0 R1#show ip route 172.16.4.3 Routing entry for 172.16.0.0/16 Known via “rip”, distance 120, metric 2 Redistributing via rip Last update from 172.16.25.129 on Serial0/1/0, 00:00:19 ago Routing Descriptor Blocks: * 172.16.25.129, from 172.16.25.129, 00:00:19 ago, via Serial0/1/0 Route metric is 2, traffic share count is 1 What route will be used for: 172.16.1.1, 172.16.1.2,172.16.2.3, and 172.16.4.3. Pg 170

  33. Multiple Routes in action • 172.16.1.1: Matches all five routes; longest prefix is /32, the route to 172.16.1.1/32. • 172.16.1.2: Matches last four routes; longest prefix is /24, the route to 172.16.1.0/24. • 172.16.2.3: Matches last three routes; longest prefix is /22, the route to 172.16.0.0/22. • 172.16.4.3: Matches the last two routes; longest prefix is /16, the route to 172.16.0.0/16. Pg 171

  34. DNS, DHCP, ARP, and ICMP • How are they used • When do we need them Pg 171

  35. DHCP • Often gathered through DHCP • The host’s IP address • The associated subnet mask • The IP address of the default gateway (router) • The IP address(s) of the DNS server(s) Pg 171

  36. DNS • Used behind the scenes to convert Name to IP addres • Web browser • E-mail client • Uses a cache on host to store information temporarily • Only asks again for same address after timeout Pg 172

  37. ICMP • Often used for with PING • Echo Request • Echo Reply • Also used to give information when trying to contact networks and hosts • Destination unreeachable • Host unreachable Pg 172

  38. DHCP, DNS, ARP, ICMP • Not used every packet • 1. If not known yet, the host uses DHCP to learn its IP address, subnet mask, DNS IP addresses, and default gateway IP address. If already known, the host skips this step. • 2. If the user references a host name not currently held in the host’s name cache, the host makes a DNS request to resolve the name into its corresponding IP address. Otherwise, the host skips this step. • 3. If the user issued the ping command, the IP packet contains an ICMP Echo Request; if the user instead used a typical TCP/IP application, it uses protocols appropriate to that application. • 4. To build the Ethernet frame, the host uses the ARP cache’s entry for the next-hop device—either the default gateway (when sending to a host on another subnet) or the true destination host (when sending to a host on the same subnet). If the ARP cache does not hold that entry, the host uses ARP to learn the information. Pg 173

  39. Any Questions?

  40. Fragmentation and MTU • MTU-Maximum transmission unit • The largest size IP packet that the network will carry • Calculated for each interface • Default for ethernet is 1500 • If a router’s interface MTU is smaller than a packet that must be forwarded, the router fragments the packet into smaller packets. Pg 173

  41. Fragmentation Pg 174

  42. Fragmentation • The IP header contains fields useful for reassembling the fragments into the original packet. • The IP header includes an ID value that is the same in each fragmented packet, as well as an offset value that defines which part of the original packet is held in each fragment. • Fragmented packets arriving out of order can be identified as a part of the same original packet and can be reassembled in the correct order using the offset field in each fragment. Pg 174

  43. MTU • mtu • Used from the config-if prompt • Sets the MTU for all Layer 3 protocols; • ip mtu • Used from the config-if prompt • Sets the value used for IP • If both are configured on an interface, the IP MTU setting takes precedence on that interface. However, if the mtu command is configured after ip mtu is configured, the ip mtu value is reset to the same value as that of the mtu command. Pg 174

  44. Any Questions?

  45. Directly Connected Subnets • Router adds networks to the routing table if configured on an interface if: • The interface is in a working state—in other words, the interface status in the show interfaces command lists a line status of up and a protocol status of up. • The interface has an IP address assigned, either through the ip address interface subcommand or by using DHCP client services. Pg 175

  46. Secondary IP Addressing • Allows a single physical interface to accept traffic for more than one IP Address Pg 176

  47. Configuring secondary address interface ethernet 0 ip address 10.1.7.252 255.255.255.0 secondary ip address 10.1.2.252 255.255.255.0 Yosemite# show ip route connected 10.0.0.0/24 is subnetted, 4 subnets C 10.1.2.0 is directly connected, Ethernet0 C 10.1.7.0 is directly connected, Ethernet0 C 10.1.129.0 is directly connected, Serial1 C 10.1.128.0 is directly connected, Serial0 Pg 177

  48. Subnet Zero • The zero subnet (or subnet zero) is the one subnet in each classful network that has all binary 0s in the subnet part of the binary version of the subnet number. In decimal, the zero subnet happens to be the same number as the classful network number. • For example in the 172.16.0.0 /18 the networks would be • 172.16.0.0-172.16.63.255 • 172.16.0.64-172.16.127.255 • 172.16.128.0-172.16.191.255 • 172.16.192.0-172.16.255.255 • Which is the subnet 0? • ip subnet-zero command allows use of the subnet 0 • Default since IOS 12.0 Pg 177

  49. Any Questions?

  50. ISL and 802.1Q Configuration on Routers • How to connect a router interface to a switch trunk port • Router needs to be able to identify VLAN IDs • Router needs an IP address for each VLAN • Must be in the same subnet as the addreses of the PCs • The router’s address for that VLAN will be the default gateway for the PCs on that VLAN Pg 178

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