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DHCP DNS P1 DHCP & Wireless Communication Methods Unicasting.pptx

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DHCP DNS P1 DHCP & Wireless Communication Methods Unicasting.pptx

  1. 1. Computer Networks Hamayun Khan Lecturer CS & IT Superior University, Lahore hamayun.khan@superior.edu.pk
  2. 2. From previous lecture
  3. 3. DNS & DHCP
  4. 4.  Explain the concept of DNS.  Explain the principle of DHCP.
  5. 5.  DNS is an acronym of Domain Name System. As the name suggests, DNS is a naming system that gives a name to any computer or service connected to a network. DNS is utterly important and everyone should use it. Without it, we’d have to visit websites through their IP addresses, rather than their domain. So, for example, if you wanted to visit our website through it’s IP address, you’d have to go to But with DNS, you can go to rosehosting.com . It’s easier to remember and it’s more user-friendly. That’s why people consider DNS “the phone book of the Internet”. Nobody wants to remember an IP, but everyone can and does remember a domain name.
  6. 6.  There’s lots of stuff going on “behind the scenes” when you visit a website. There’s a communicating relationship between a few servers and your computer.These are the usual steps they take: 1. The user enters the website’s domain in the address bar 2. The browser and OS check their local cache 3. The Resolver checks the local cache 4. The root server checks the local cache 5. The root server forwards the resolver to the TLD server 6. Receiving the answer
  7. 7.  Forward Lookup Zone  Reverse Lookup Zone
  8. 8. Dynamic Host Configuration Protocol
  9. 9.  In IP environment, before a computer can communicate to another one, they need to have their own IP addresses.  There are two ways of configuring an IP address on a device:  Static: Statically assign an IP address. This means we manually type an IP address for this computer  Dynamic Use a protocol so that the computer can obtain its IP address automatically.
  10. 10.  Lease Generation Process  DORA Process  Discover  Offer  Request  Acknowledgement  Four step Process
  11. 11. Range of IP Addresses Different Scopes for different subnets
  12. 12.  DHCPDISCOVER message  Destination IP address (broadcast)  Destination MAC address FF-FF-FF-FF-FF-FF (broadcast)  Source IP address  Source MAC Address  Try to find out a DHCP Server
  13. 13.  DHCPOFFER message  IP Address  Subnet Mask  Default Gateway  LeaseTime  DNS  Destination IP address (broadcast)  Destination MAC address of Client (unicast)
  14. 14.  DHCPREQUEST message  Destination IP address (broadcast)  Destination MAC address of FF-FF-FF-FF-FF-FF (broadcast)  Source IP address of  Way to inform other DHCP Servers
  15. 15.  DHCPACKNOWLE DGEMENT  Destination IP address  Destination MAC address of Client
  16. 16.  By default, lease period is limited to 8 days.  Clients attempt to renew its lease as 50% of the lease duration has expired.
  17. 17.  If the client cannot find a DHCP server then It may auto assign an IP address from a reserved range to or simply have an IP address of
  18. 18.  ipconfig ./all -This command will show IP and DNS settings  ipconfig ./release -This command will release the IP address from DHCP  ipconfig ./renew -This command will renew the IP address using DHCP
  19. 19. THANKS
  20. 20.  The IP address can either be permanent or timed  A permanent address is never reused for another client  Timed leases expire after a certain amount of time  Windows clients attempt to renew their lease after 50% of the lease time has expired.  A DHCP server may either honor or reject a renew request
  21. 21.  If the client cannot find a DHCP server then It may auto assign an IP address from a reserved range to or simply have an IP address of
  22. 22.  Automatic Private IP Addressing (APIPA) is a feature in operating systems (such as Windows) that enables computers to automatically self-configure an IP address and subnet mask when their DHCP server isn't reachable.The IP address range for APIPA is 169.254
  23. 23.  (Automatic Private IP Addressing)The Windows function that provides DHCP auto configuration addressing. APIPA assigns a class B IP address from 169.254. 0.0 to 169.254. 255.255 to the client when a DHCP server is either permanently or temporarily unavailable.
  24. 24.  When a DHCP client boots up, it looks for a DHCP server in order to obtain network parameters. If the client can’t communicate with the DHCP server, it uses APIPA to configure itself with an IP address from the APIPA range.This way, the host will still be able to communicate with other hosts on the local network segment that are also configured for APIPA.
  25. 25.  The APIPA service also checks regularly for the presence of a DHCP server (every three minutes). If it detects a DHCP server on the network, the DHCP server replaces the APIPA networking addresses with dynamically assigned addresses.
  26. 26.  It relieves the network administrator of a great deal of manual configuration work.  The ability for a device to be moved from network to network and to automatically obtain valid configuration parameters for the current network can be of great benefit to mobile users.  Because IP addresses are only allocated when clients are actually active, it is possible, by the use of reasonably short lease times and the fact that mobile clients do not need to be allocated more than one address, to reduce the total number of addresses in use in an organization.  Centralized, simpler management of IP addressing:You can manage IP addressing from a central location.  Because the system assigns IP addresses, it leads to less incorrect configurations of IP addresses.This is mainly due to IP configuration information being entered at one location, and the server distributing this information to clients.  Duplicated IP addresses are prevented.  IP addresses are also preserved.  DHCP servers only allocate IP addresses to clients when they request them.  Dynamic IP addressing through DHCP easily scales from small to large networking environments.
  27. 27.  The DHCP server can be a single point of failure in networking environments that only have one DHCP server.  If your network has multiple segments, you have to perform either of the following additional configurations:  Place a DHCP server on each segment  Place a DHCP relay agent on each segment  All incorrectly defined configuration information will automatically be propagated to your DHCP clients.  Uses UDP, an unreliable and insecure protocol.  Potentially unauthorized clients  Malicious client could exhaust address pool  Malicious server (Rogue server)  Supply incorrect configuration parameters
  28. 28.  ipconfig ./all -This command will show IP and DNS settings  ipconfig ./release -This command will release the IP address from DHCP  ipconfig ./renew -This command will renew the IP address using DHCP
  29. 29.  DNS stands for Domain Name System  To identify an entity,TCP/IP protocols use the IP address, which uniquely identifies the connection of a host to the Internet.  However, people prefer to use names instead of numeric addresses.  Therefore, we need a system that can map a name to an address or an address to a name.
  30. 30.  Users generally prefer names to numbers  Computers prefer numbers to names  DNS provides the mapping between the name and numbers  i.e. domain name to IP address
  31. 31.  In the Internet the domain name space is divided into the Following sections:  Generic Domains  Country Domains
  32. 32.  The generic domains define registered hosts according to their generic behavior.
  33. 33.  The country domains section uses two- character country abbreviations  e.g., pk for Pakistan
  34. 34.  Each name is made of several parts separated by dot (.)  The first part can define the name of an organization.  The second part can define the nature of the organization. i.e. commercial, education, organization etc.  Some domain names have other parts like the starting parts will define departments in the organization & the ending parts will specify the country or sub type of organization.  E.g. www.yahoo.com  For each new domain registartion, first it is check that some one else don’t has domain name, if not then it is registered.
  35. 35.  For simplicity the domain name is design hierarchal as shown in figure.
  36. 36.  Forward Lookup Zones—Forward Lookup Zones allow the DNS Server to resolve queries where the client sends a name to the DNS Server to request the IP address of the requested host. Reverse Lookup Zones— Reverse DNS zones perform the opposite task as Forward Lookup Zones.
  37. 37.  On the Day of Judgment, no step shall a man stir until he has answered questions on five aspects of his worldly existence: His life and how he spent it; his knowledge and what use he made of it; his wealth—how he acquired and spent it; and his body, and how he utilized it.  HADITH OF AT-TIRMIDI ONTHE AUTHORITYOF ABU HURAYRAH
  38. 38.  How data / Information can be sent from source to destination.  Either source have single destination or multiple destination.  How data reach destination and router take decision.  We will study here  Unicasting  Multi casting  Multiple casting  Broadcasting
  39. 39. • In unicasting, there is one source and one destination network. • The relationship between the source and the destination network is one to one. • Each router in the path of the datagram tries to forward the packet to one and only one of its interfaces. (As Shown in the Figure).
  40. 40. • Figure shows a small internet in which a unicast packet needs to be delivered from a source computer to a destination computer attached to N6. • Router R1 is responsible to forward the packet only through interface 3; router R4 is responsible to forward the packet only through interface 2. When the packet arrives to N6,
  41. 41.  In multicasting, there is one source and a group of destinations.  The relationship is one to many.  In this type of communication, the source address is a unicast address, but the destination address is a group address.
  42. 42.  In multicasting, a multicast router may have to send out copies of the same datagram through more than one interface.  In Figure 2, router R1 needs to send out the datagram through interfaces 2 and 3. Similarly, router R4 needs to send out the datagram through both its interfaces. Router R3, however, knows that there is no member belonging to this group in the area reached by interface 2; it only sends out the datagram through interface 1.
  43. 43.  We need to distinguish between multicasting and multiple unicasting.  Figure 3 clarify both concepts.
  44. 44.  Multicasting = Single source multi destination but all will have single copy.  Multiple Unicasting = Single source multi destination but one copy for each destination separately.  Multicasting starts with one single packet from the source that is duplicated by the routers.  Note that only one single copy of the packet travels between any two routers.  In multiple unicasting, several packets start from the source. If there are four destinations, for example, the source sends four packets, each with a different unicast destination address.  Note that there may be multiple copies traveling between two routers.  For example, when a person sends an e-mail message to a group of people, this is multiple unicasting.The e-mail software creates replicas of the message, each with a different destination address, and sends them one by one.
  45. 45.  Multicasting is more efficient than multiple unicasting. In Figure 3, we can see how multicasting requires less bandwidth than multiple unicasting.  In multiple unicasting, some of the links must handle several copies.  In multiple unicasting, the packets are created by the source with a relative delay between packets.  If there are 1,000 destinations, the delay between the first and the last packet may be unacceptable.  In multicasting, there is no delay because only one packet is created by the source.
  46. 46. 1. Information Spreading:  Businesses often need to send information to their customers. If the nature of the information is the same for each customer, it can be multicast.  In this way a business can send one message that can reach many customers. 2. Spreading of News:  In a similar manner news can be easily passed around through multicasting.  One single message can be sent to those interested in a particular topic.
  47. 47. 3. Teleconferencing  Teleconferencing involves multicasting.  The individuals attending a teleconference all need to receive the same information at the same time. 4. Distance Learning  One growing area in the use of multicasting is distance learning.  Lessons taught by one single professor can be received by a specific group of students.
  48. 48.  In broadcast communication, the relationship between the source and the destination is one to all.  There is only one source, but all of the other hosts are the destinations.  The Internet does not support broadcasting because of the huge amount of traffic it would create.  Imagine the traffic generated in the Internet if one person wanted to send a message to everyone else connected to the Internet.
  49. 49.  In unicasting, the router forwards the received datagram through only one of its interfaces.  i.e. One Source One Destination  In multicasting, a multicast router may have to send out copies of the same datagram through more than one interface.  i.e. One Source and Multi Destination.  In multiple Unicasting, a single source having multiple destination but each destination having separately copy.  i.e. One Source and Multi Destination separate copy for each.  In broadcast communication, the relationship between the source and the destination is one to all.  i.e. One Source and all destination
  50. 50.  The main difference between Ping and Traceroute is that Ping is a quick and easy utility to tell if the specified server is reachable and how long will it take to send and receive data from the server whereas Traceroute finds the exact route taken to reach the server and time taken by each step (hop).