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  1. 1. Ch 6 - Chapter 6 Addressing the Network – IPv4
  2. 2. Objectives <ul><li>Explain the structure of IP addressing and demonstrate the ability to convert between 8-bit binary and decimal numbers </li></ul><ul><li>Given an IPv4 address, classify by type and describe how it is used in the network </li></ul><ul><li>Explain how addresses are assigned to networks by ISPs and within networks by administrators </li></ul><ul><li>Determine the network portion of the host address and explain the role of the subnet mask in dividing networks </li></ul><ul><li>Given IPv4 addressing information and design criteria, calculate the appropriate addressing components </li></ul><ul><li>Use common testing utilities to verify and test network connectivity and operational status of the IP protocol stack on a host </li></ul>Ch 6 -
  3. 3. IPv4 Addressing Structure <ul><li>IPv4 is the current form of addressing used on the Internet </li></ul><ul><li>Uses the dotted decimal structure to represent the 32-bit IP address </li></ul>Ch 6 -
  4. 4. IP Address <ul><li>Each device on a network must be uniquely defined </li></ul><ul><ul><li>assigned a 32-bit address </li></ul></ul><ul><ul><li>used to identify the source and destination addresses </li></ul></ul><ul><li>The 32-bit address is written in a dotted decimal format </li></ul><ul><ul><li>each byte (or octet) is represented in decimal and separated by a dot </li></ul></ul><ul><li>Contains the network and host portions </li></ul><ul><ul><li>some portion of the higher-order bits represents the network address </li></ul></ul><ul><ul><li>the number of bits in the host portion determines the number of hosts within the network </li></ul></ul>Ch 6 - network host
  5. 5. Decimal Numbering System <ul><li>In the decimal numbering system, the radix (or base) is 10 </li></ul><ul><ul><li>has ten digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 </li></ul></ul><ul><li>245 = (2 x 100) + (4 x 10) + (5 x 1) </li></ul>Ch 6 - 10 2 10 1 10 0 100 10 1 2 4 5 200 + 40 + 5 245
  6. 6. Binary Numbering System <ul><li>In the binary numbering system, the radix (or base) is 2 </li></ul><ul><ul><li>has two digits 0 and 1 </li></ul></ul><ul><li>**11110101 = (1x128)+(1x64)+(1x32)+(1x16)+(0x8)+(1x4)+(0x2)+(1x1) = 245 </li></ul><ul><li>Each octet has a minimum value of 0 and a maximum value of 255 </li></ul>Ch 6 -
  7. 7. Binary Number Characteristics <ul><li>The decimal value of any binary number is odd if the binary value of the least significant bit (LSB) is 1 </li></ul><ul><li>The decimal value of any binary number is even if the binary value of the least significant bit (LSB) is 0 </li></ul>Ch 6 - X = 0 or 1 128 64 32 16 8 4 2 1 X X X X X X X 0 even LSB 128 64 32 16 8 4 2 1 X X X X X X X 1 odd LSB
  8. 8. Binary to Decimal Conversion <ul><li>Divide the 32 bits into 4 octets </li></ul><ul><li>Convert each octet to decimal </li></ul><ul><li>Add a “dot” between each decimal </li></ul>Ch 6 -
  9. 9. Decimal to Binary Conversion <ul><li>Start by determining if the decimal number is equal to or greater than the largest decimal value represented by the most significant bit (MSB) </li></ul>Ch 6 -
  10. 10. Dotted Decimal to Binary Conversion <ul><li>Separate and convert each decimal number separately </li></ul><ul><li>Arrange each octet into the 32-bit address </li></ul>Ch 6 -
  11. 11. Types of Address <ul><li>Network address </li></ul><ul><ul><li>a way to refer to the network as a whole </li></ul></ul><ul><li>Broadcast address </li></ul><ul><ul><li>a special address used to send packets to every hosts in the network that shares the same network portion of the address </li></ul></ul><ul><li>Host address </li></ul><ul><ul><li>each host in the network has a unique address </li></ul></ul>Ch 6 -
  12. 12. Network Prefix <ul><li>The prefix length is the number of bits in the address that gives the network (or subnetwork) portion </li></ul><ul><ul><li>/25 is the prefix length that indicates the first 25 bits are the network address => Subnet Increment = 128 </li></ul></ul>Ch 6 -
  13. 13. 5 Shortcuts to Remember <ul><li>/27=> 111 00000 – network portion , host portion </li></ul><ul><li>Subnet Increment => 0,32,64,96,128,160,192,224 </li></ul><ul><li>Subnet Mask </li></ul><ul><li>8 Subnet = 2 3 => 3 network bits </li></ul><ul><li>IP AND Mask = Subnet/Network </li></ul>Ch 6 - Increment 128 64 32 16 8 4 2 1 Subnet Bits 1 2 3 4 5 6 7 8 Mask 128 192 224 240 248 252 254 255 Subnet Bits 1 2 3 4 5 6 7 8
  14. 14. Calculating Network , Hosts and Broadcast Addresses <ul><li>A network address contains all zeros in the host portion </li></ul><ul><li>The first useable host address has a 0 for each host bit except the last bit, which is a 1, in the host portion </li></ul><ul><li>The last useable host address has a 1 for each host bit except the </li></ul>Ch 6 - <ul><li>last bit, which is a 0, in the host portion </li></ul><ul><li>The broadcast address contains all ones in the host portion </li></ul>
  15. 15. IP Address Example ( Popular Exam Question ) <ul><li>Last octet is 148 (10010100) </li></ul><ul><ul><li>1001 is part of the network portion (28=8+8+8+4) </li></ul></ul><ul><ul><li>0100 is the host portion </li></ul></ul>Ch 6 -
  16. 16. Unicast Transmission <ul><li>The process of sending a packet from one host to another host </li></ul><ul><ul><li>normal host-to-host communication </li></ul></ul><ul><li>Unicast packets use the host address of the destination device as the destination address and can be routed through an internetwork </li></ul>Ch 6 -
  17. 17. Broadcast Transmission <ul><li>The process of sending a packet from one host to all hosts in the network </li></ul><ul><ul><li>packet uses a special broadcast address as the destination address </li></ul></ul><ul><li>Used for locating special services/devices for which the address is not known or when the host needs to provide information to all hosts on the network </li></ul>Ch 6 - <ul><ul><li>mapping upper-layer addresses to lower-layer addresses </li></ul></ul><ul><ul><li>requesting an address </li></ul></ul><ul><ul><li>exchanging routing information by routing protocols </li></ul></ul>
  18. 18. Broadcast Transmission (cont’d) <ul><li>Directed broadcast </li></ul><ul><ul><li>is sent to all hosts on a specific network , usually a non-local network </li></ul></ul><ul><ul><li>although routers do not forward directed broadcasts, they may be configured to do so </li></ul></ul><ul><li>Limited broadcast </li></ul><ul><ul><li>is used for communication that is limited to hosts on the local network </li></ul></ul><ul><ul><li>packets used a destination address of (all ones) </li></ul></ul><ul><ul><li>packets addressed to the limited broadcast address will only appear on the local network </li></ul></ul>Ch 6 -
  19. 19. Multicast Transmission <ul><li>The process of sending a packet from one host to a selected group of hosts </li></ul><ul><ul><li>designed to conserve bandwidth </li></ul></ul><ul><li>A special block of addresses from to is used for multicast groups addressing </li></ul>Ch 6 - <ul><li>Hosts that wish to receive particular multicast data are called multicast clients </li></ul><ul><ul><li>video and audio distribution </li></ul></ul><ul><ul><li>routing information exchange by routing protocols </li></ul></ul><ul><ul><li>software distribution </li></ul></ul><ul><ul><li>news feeds </li></ul></ul>
  20. 20. Reserved IPv4 Address <ul><li>IPv4 address range is from to </li></ul><ul><ul><li>not all these addresses can be used for host addresses in unicast transmission </li></ul></ul><ul><li>Multicast and experimental addresses are reserved for special purposes </li></ul>Ch 6 -
  21. 21. Public and Private Addresses <ul><li>Public addresses </li></ul><ul><ul><li>designated for use in networks that are accessible on the Internet </li></ul></ul><ul><li>Private addresses </li></ul><ul><ul><li>blocks of addresses that are used in private networks that require no or limited Internet access </li></ul></ul>Ch 6 -
  22. 22. Private Addresses <ul><li>Three blocks of IP address space for private networks </li></ul><ul><li>(online assessment question) </li></ul><ul><ul><li> to ( </li></ul></ul><ul><ul><li> to ( </li></ul></ul><ul><ul><li> to ( </li></ul></ul><ul><li>Routers do not have routes to forward private address to the appropriate private networks </li></ul><ul><li>Routers can use a service, called network address translation (NAT), to translate private addresses to public addresses </li></ul><ul><ul><li>NAT allows the hosts in a private network to “borrow” a public address for communicating to outside networks </li></ul></ul>Ch 6 -
  23. 23. Special IPv4 Addresses <ul><li>Network and broadcast addresses </li></ul><ul><ul><li>the first, network, and last, broadcast, addresses cannot be assigned to hosts within each network </li></ul></ul><ul><li>Default route ( /8) </li></ul><ul><ul><li>used as a “catch all” route when a more specific route is NOT available </li></ul></ul><ul><li>Loopback address( ) </li></ul><ul><ul><li>a special address that hosts use to direct traffic to themselves </li></ul></ul><ul><ul><li>entire address block, to, is reserved </li></ul></ul><ul><li>Link-local addresses (Routers will not forward packets with link-local addresses) </li></ul><ul><ul><li> to ( </li></ul></ul><ul><ul><li>addresses are assigned to the local host by the operating system in environments where no IP configuration is available </li></ul></ul><ul><ul><li>used in a small peer-to-peer network or for a host that could not automatically obtain an address from a DHCP server </li></ul></ul><ul><ul><li>a host must not send an IPv4 link-local destination address to any router for forwarding and should set the TTL for these packets to 1 </li></ul></ul>Ch 6 -
  24. 24. Special IPv4 Addresses (cont’d) <ul><li>TEST-NET address (Routers will not forward packets with TEST-NET addresses) </li></ul><ul><ul><li>address block to is reserved for teaching and learning purposes </li></ul></ul>Ch 6 -
  25. 25. IP Address Classes <ul><li>Class A address </li></ul><ul><ul><li>designed to support very large networks with more than 16 million hosts </li></ul></ul><ul><ul><li>first octet has a value of 1 to 126 </li></ul></ul><ul><ul><li>used a fixed /8 prefix with the first octet to indicate the network address </li></ul></ul><ul><ul><li>remaining three octets are used for host addresses </li></ul></ul><ul><li>Class B address </li></ul><ul><ul><li>designed to support the needs of moderate to large size networks with more than 65,000 hosts </li></ul></ul><ul><ul><li>first octet has a value of 128 to 191 </li></ul></ul><ul><ul><li>first and second octets represent the network </li></ul></ul><ul><li>Class C address ( 192 to 223 ) </li></ul><ul><ul><li>intended to provide addresses for small networks with a maximum of 254 hosts </li></ul></ul>Ch 6 -
  26. 26. IP Address Classes (cont’d) <ul><ul><li>first octet has a value of 192 to 223 </li></ul></ul><ul><ul><li>first three octets represent the network </li></ul></ul>Ch 6 -
  27. 27. Address Planning and Documentation <ul><li>Preventing duplication of address </li></ul><ul><ul><li>each host in an internetwork must have a unique address </li></ul></ul><ul><ul><li>could assign a same address to more than one hosts </li></ul></ul><ul><li>Providing and controlling access </li></ul><ul><ul><li>access to resources , such as servers, can be controlled using Layer 3 address </li></ul></ul><ul><ul><li>blocking access to a random address assignment for a server is difficult and client may not locate this resource </li></ul></ul><ul><li>Monitoring security and performance </li></ul><ul><ul><li>examine network traffic looking for addresses that are generating or receiving excessive packets </li></ul></ul>Ch 6 -
  28. 28. Using Private Addresses <ul><li>Will there be more devices connected to the network than public addresses allocated by the ISP? </li></ul><ul><li>Will the devices need to be accessed from outside the local network? </li></ul><ul><li>If the devices that may be assigned private addresses require to access the Internet, is this network capable of providing a NAT service? </li></ul>Ch 6 -
  29. 29. Static Addressing for End Devices <ul><li>A network administrator must manually configure the network information for a host </li></ul><ul><li>Static assignment of address can provide increased control of network resources </li></ul><ul><ul><li>time consuming to enter the information on each host </li></ul></ul>Ch 6 - <ul><ul><li>necessary to maintain an accurate list of address for each device to prevent address duplication </li></ul></ul>
  30. 30. Dynamic Addressing for End Devices <ul><li>Preferred method of assigning IP addresses to hosts on large networks using DHCP </li></ul><ul><ul><li>address is leased for a period of time </li></ul></ul><ul><ul><li>reduces the burden of support staff </li></ul></ul><ul><ul><li>eliminates entry errors </li></ul></ul>Ch 6 -
  31. 31. Assigning Addresses to Other Devices <ul><li>Addresses for servers and peripherals eg: Printer </li></ul><ul><ul><li>should have a static address </li></ul></ul><ul><ul><li>servers and peripherals are concentration points for network traffic </li></ul></ul><ul><li>Addresses for hosts that are accessible from Internet </li></ul><ul><ul><li>the addresses for these devices should be static </li></ul></ul><ul><ul><li>must have a public space address associated with it </li></ul></ul><ul><li>Addresses for intermediary devices, eg: Router, Switch </li></ul><ul><ul><li>intermediary devices are also a concentration point for network traffic </li></ul></ul><ul><ul><li>may be used as hosts to configure, monitor, or troubleshoot network operation </li></ul></ul><ul><ul><li>addresses are assigned manually to these devices </li></ul></ul>Ch 6 -
  32. 32. Assigning Addresses to Other Devices (cont’d) <ul><li>Routers and firewalls </li></ul><ul><ul><li>each interface is assigned an address manually </li></ul></ul><ul><ul><li>these devices are used for packet filtering </li></ul></ul>Ch 6 -
  33. 33. IP Address Allocation <ul><li>Internet Assigned Numbers Authority ( IANA ) </li></ul><ul><ul><li>master holder of the IP address </li></ul></ul><ul><ul><li>IP multicast and IPv6 are obtained directly from IANA </li></ul></ul><ul><li>Regional Internet Registries (RIR) </li></ul><ul><ul><li>remaining IPv4 address space is managed by RIR since mid 1990s </li></ul></ul>Ch 6 -
  34. 34. Internet Service Providers ( ISP s) (Eg: Starhub, Singtel) <ul><li>Role </li></ul><ul><ul><li>supply a small number of useable IPv4 addresses (6 or 14) to their customers as part of their services </li></ul></ul><ul><li>Services </li></ul><ul><ul><li>DNS services, e-mail services and website </li></ul></ul><ul><li>Tiers </li></ul><ul><ul><li>Tier 1 ISPs provide reliability and speed with multiple connections to the Internet backbone </li></ul></ul><ul><ul><li>Tier 2 ISPs generally focus on business customers </li></ul></ul><ul><ul><li>Tier 3 ISPs focus on the retail and home market in a specific locale </li></ul></ul>Ch 6 -
  35. 35. ISP Tiers Ch 6 -
  36. 36. IPv6 Overview <ul><li>Improved packet handling </li></ul><ul><li>Increased scalability and longevity </li></ul><ul><li>QoS mechanisms </li></ul><ul><li>Integrated security </li></ul>Ch 6 -
  37. 37. IPv6 Capabilities <ul><li>128-bit hierarchical addressing </li></ul><ul><ul><li>to expand addressing capabilities </li></ul></ul><ul><li>Header format simplification (online assessment question) </li></ul><ul><ul><li>to improve packet handling </li></ul></ul><ul><li>Improved support for extensions and options </li></ul><ul><ul><li>for increased scalability, longevity and improved packet handling </li></ul></ul><ul><li>Flow labeling capabilities </li></ul><ul><ul><li>QoS mechanism </li></ul></ul><ul><li>Authentication and privacy capabilities </li></ul><ul><ul><li>to integrate security </li></ul></ul>Ch 6 -
  38. 38. Subnet Mask <ul><li>The prefix and subnet mask are different ways of representing the same thing – the network portion of an IP address </li></ul>Ch 6 -
  39. 39. Subnet Mask Template Ch 6 - 128 64 32 16 8 4 2 1 Address bits 128 192 224 240 248 252 254 255 Possible Subnet Address 1 1 1 1 1 1 1 1
  40. 40. The AND Operation <ul><li>A host address is logically AND ed with its subnet mask to determine the network address to which the host is associated </li></ul><ul><li>Routers use ANDing to determine an acceptable route for an incoming packet </li></ul><ul><ul><li>the destination network address is compared to the routes from the routing table </li></ul></ul>Ch 6 - <ul><li>An originating host must determine if a packet should be sent directly to a host in a local network or be directed to the gateway </li></ul>
  41. 41. The ANDing Process <ul><li>Convert host address to binary </li></ul><ul><li>Convert prefix to binary subnet mask </li></ul><ul><li>AND each bit of host address with corresponding bit of mask </li></ul><ul><li>Convert binary network address to decimal </li></ul>Ch 6 - <ul><li>1 AND 1 = 1 </li></ul><ul><li>0 AND 1 = 0 </li></ul><ul><li>1 AND 0 = 0 </li></ul><ul><li>0 AND 0 = 0 </li></ul>
  42. 42. Basic Subnetting <ul><li>Subnetting allows for creating multiple logical networks from a single address block </li></ul><ul><li>Subnets are created using one or more of the host bits as network bits </li></ul><ul><ul><li>done by extending the mask to borrow some of the bits from the host portion to create additional network bits </li></ul></ul>Ch 6 -
  43. 43. Calculating Subnets and Hosts <ul><li>The number of subnets is calculated using 2 n , where n is the number of bits borrowed </li></ul><ul><ul><li>2 1 = 2 subnets </li></ul></ul><ul><ul><li>the more bits borrowed, the more subnets can be defined </li></ul></ul><ul><li>The number of useable hosts per subnet is calculated using 2 h - 2 where h is the number of host bits left </li></ul><ul><ul><li>2 7 – 2 = 126 useable hosts per subnet </li></ul></ul><ul><ul><li>with each bit borrowed, fewer host addresses are available per subnet </li></ul></ul>Ch 6 -
  44. 44. Subnetting Example 1 <ul><li>Need to borrow a minimum of 2 host bits to cater for 3 subnets </li></ul><ul><ul><li>2 2 = 4 subnets </li></ul></ul>Ch 6 -
  45. 45. Subnetting Example 1 (cont’d) <ul><li>6 host bits are left in the last octet </li></ul><ul><li>2 6 – 2 = 62 hosts per subnet </li></ul>Ch 6 -
  46. 46. Subnetting Example 2 <ul><li>Need to borrow a minimum of 3 host bits to cater for 6 subnets </li></ul><ul><ul><li>2 3 = 8 subnets </li></ul></ul>Ch 6 -
  47. 47. Subnetting Example 2 (cont’d) <ul><li>5 host bits are left in the last octet </li></ul><ul><li>2 5 – 2 = 30 hosts per subnet </li></ul>Ch 6 -
  48. 48. Fixed Length Subnet Mask (FLSM) <ul><li>Using traditional subnetting or FLSM, each subnet is allocated the same number of host addresses </li></ul><ul><ul><li>these fixed size address block would be efficient if all subnets have the same requirements for the number of hosts </li></ul></ul>Ch 6 - 2 5 – 2 = 30 hosts per subnet
  49. 49. Variable Length Subnet Mask ( VLSM ) <ul><li>VLSM was designed to maximize addressing efficiency </li></ul><ul><ul><li>each WAN link requires 2 host addresses </li></ul></ul><ul><li>Breaks up a subnet into a smaller subnet </li></ul>Ch 6 -
  50. 50. Using FLSM <ul><li>Standard subnetting would lock each subnet into blocks of 62 hosts </li></ul><ul><ul><li>2 6 – 2 = 62 hosts to meet the highest number of hosts required </li></ul></ul>Ch 6 -
  51. 51. Using FLSM (cont’d) <ul><li>The network has a given address block of </li></ul><ul><li>Need 6 host bits to support the largest user requirement </li></ul><ul><li>The unused addresses are especially evident when the LAN routers support 10 users only </li></ul><ul><li>Each WAN link has 60 unused address </li></ul>Ch 6 -
  52. 52. Using VLSM – Step 1 <ul><li>Calculate a subnet from the original block to accommodate the largest LAN, i.e. 58 hosts </li></ul><ul><li>Keep 6 host bits to cater for the 58 hosts </li></ul><ul><ul><li>2 6 – 2 = 62 useable host addresses </li></ul></ul><ul><ul><li>mask for last octet 11000000 </li></ul></ul><ul><li>2 bits are borrowed to create 4 possible subnets </li></ul><ul><ul><li> (subnet 0) </li></ul></ul><ul><ul><li> (subnet 1) </li></ul></ul><ul><ul><li> (subnet 2) </li></ul></ul><ul><ul><li> (subnet 3) </li></ul></ul><ul><li>Assign subnet 0 ( to this LAN </li></ul><ul><ul><li>3 subnets left unused </li></ul></ul>Ch 6 -
  53. 53. Using VLSM – Step 2 <ul><li>Consider the LAN with the next fewer hosts, i.e. 26 hosts </li></ul><ul><li>Require 5 host bits to accommodate 26 hosts </li></ul><ul><ul><li>2 5 – 2 = 30 useable host addresses </li></ul></ul><ul><ul><li>mask for the last octet is 11100000 </li></ul></ul><ul><li>Use the next available address of to create an address block for this subnet </li></ul><ul><li>One more bit is borrowed from the above subnet </li></ul><ul><ul><li> </li></ul></ul><ul><li>This subnet,, creates two more subnets </li></ul><ul><ul><li> (subnet 0)  </li></ul></ul><ul><ul><li> (subnet 1)  </li></ul></ul><ul><li>Assign the to this LAN </li></ul><ul><ul><li>1 subnet left unused </li></ul></ul>Ch 6 -
  54. 54. Using VLSM – Step 3 <ul><li>Consider the LAN with the next fewer hosts, i.e. 10 hosts </li></ul><ul><li>Require 4 host bits to accommodate 10 hosts </li></ul><ul><ul><li>2 4 – 2 = 14 useable host addresses </li></ul></ul><ul><ul><li>mask for the last octet is 11110000 </li></ul></ul><ul><li>Use the next available address of to create an address block for this subnet </li></ul><ul><li>One more bit is borrowed from the above subnet </li></ul><ul><ul><li> </li></ul></ul><ul><li>This subnet,, creates two more subnets </li></ul><ul><ul><li> (subnet 0)  </li></ul></ul><ul><ul><li> (subnet 1)  </li></ul></ul><ul><li>Assign both these subnets to the LANs with the same number of hosts </li></ul><ul><ul><li>no subnet left </li></ul></ul>Ch 6 -
  55. 55. Using VLSM – Step 4 <ul><li>Point-to-point WAN links require two host addresses </li></ul><ul><li>Require two host bits to provide two host addresses </li></ul><ul><ul><li>2 2 – 2 = 2 useable host addresses </li></ul></ul><ul><ul><li>mask for the last octet is 11111100 </li></ul></ul><ul><li>Use the next available address of to create an address block for this subnet </li></ul><ul><li>Four more bits are borrowed from the above subnet </li></ul><ul><ul><li> </li></ul></ul><ul><li>This subnet,, creates 16 more subnets </li></ul><ul><ul><li> (subnet 0)  </li></ul></ul><ul><ul><li> (subnet 1)  </li></ul></ul><ul><ul><li> (subnet 2)  </li></ul></ul><ul><ul><li> (subnet 3)  </li></ul></ul>Ch 6 -
  56. 56. Using VLSM – Step 5 <ul><li>Calculate the address range and broadcast address for each subnet </li></ul><ul><li>Document the host requirements, subnet addresses, address range, broadcast addresses and network prefix </li></ul>Ch 6 -
  57. 57. Using VLSM – Network Diagram Ch 6 -
  58. 58. Testing Connectivity <ul><li>Ping is a utility for testing IP connectivity between hosts </li></ul><ul><ul><li>sends out requests for responses from a specified host address </li></ul></ul><ul><ul><li>provides a display output with a summary of the responses including the success rate and average round-trip time </li></ul></ul><ul><ul><li>uses Internet Control Message Protocol ( ICMP ), a Layer 3 protocol (Network) </li></ul></ul><ul><li>Source device sends an ICMP echo request datagram to the destination device </li></ul><ul><ul><li>destination device responds with an ICMP echo reply if it receives the echo request </li></ul></ul><ul><ul><li>ping measures the time taken for the reply </li></ul></ul>Ch 6 - echo request echo reply source destination
  59. 59. Testing Local TCP/IP Stack Ch 6 -
  60. 60. Testing Connectivity to Local Gateway <ul><li>Test the host’s connectivity to the router interface </li></ul><ul><li>Verify the correct address is configured as the default gateway </li></ul>Ch 6 - <ul><li>Security applied to the router interface may prevent it from responding to echo requests </li></ul>
  61. 61. Testing Connectivity to Remote LAN <ul><li>The ping command can also be used to verify the availability or reachability of a remote device </li></ul><ul><li>Lack of ping response could be due to security restrictions and not because of non-operational elements of the network </li></ul>Ch 6 -
  62. 62. Testing The Path <ul><li>Traceroute , or tracert , is a utility to observe the path between two hosts </li></ul><ul><li>The trace generates a list of hops that were successfully reached along the path </li></ul><ul><ul><li>if the data reaches the destination, the trace lists the interface on every router in the path </li></ul></ul><ul><ul><li>if the data fails at some hop along the way, the trace lists the address of the last router that responded </li></ul></ul><ul><li>An asterisk (*) is used to indicate a lost packet </li></ul><ul><li>Traceroute makes use of the TTL field </li></ul><ul><ul><li>the initial value in the TTL field in the first message is set to 1, allowing a single hop to the first router </li></ul></ul><ul><ul><li>traceroute then progressively increments the TTL field for each message until the destination is reached </li></ul></ul>Ch 6 -
  63. 63. ICMP <ul><li>IP uses the services of ICMP to send messages in the event of certain errors </li></ul><ul><ul><li>ICMP messages provide feedback about issues related to the processing of IP packets under certain conditions </li></ul></ul><ul><ul><li>ICMP messages are not intended to make IP reliable </li></ul></ul><ul><li>ICMP provides control and error messages </li></ul><ul><ul><li>host confirmation – echo request and echo reply </li></ul></ul><ul><ul><li>unreachable destination or service </li></ul></ul><ul><ul><li>time exceeded </li></ul></ul><ul><ul><li>route redirection </li></ul></ul><ul><ul><li>source quench </li></ul></ul><ul><li>ICMP messages are often not allowed for security reasons </li></ul>Ch 6 -