1. Unit 7: DHCP, APIPA and NTP

2. Static versus dynamic IP addressing Dynamic IP addresses can change each time you connect to the Internet, while static IP addresses are reserved for you statically and don't change over time. A Static Ip is an IP that has been manually entered in to the computer,if two computers are assigned the same IP address this can cause a problem. You can use Static IP address for : VOIP, VPN,Servers and Printers.

3. Dynamic IP address Dynamic IP address usually given out by ISPs, the DHCP servers can assign Ips to People on the network. You should never use a Dynamic IP on VOIP, VPN, Servers, Printers as the IP changes often and this would make them less reliable than Static IP address. You Could get Disconnected when using the service.

4. Bootstrap Protocol (BOOTP) was developed as a means of supplying a full set of configuration parameters (IP address, subnet mask, default gateway, DNS addresses, and so on). The additional parameters are provided in an executable boot file downloaded to the host using Trivial File Transfer Protocol (TFTP)

5. Dynamic Host Configuration Protocol (DHCP) Dynamic Host Configuration Protocol ( DHCP ) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway.

6. D ynamic H ost C onfiguration P rotocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses. The Discover packets get to the DHCP server by the Router. The DHCP server will then give an IP to the PC from a select Range. Then the computer will get the IP Uses Ports 67 –inbound user requests and 68-clients accept date from the server.

7. DHCP client initialisation

8. DHCP Simplifies Network Administration Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for Internet subscribers.

9. Automatic Private IP Addressing (APIPA) Short for A utomatic P rivate IP A ddressing, a feature of later Windows operating systems. With APIPA, DHCP clients can automatically self-configure an IP address and subnet mask when a DHCP server isn't available. When a DHCP client boots up, it first looks for a DHCP server in order to obtain an IP address and subnet mask. If the client is unable to find the information, it uses APIPA to automatically configure itself with an IP address from a range that has been reserved especially for Microsoft.

10. The IP address range is 169.254.0.1 through 169.254.255.254. The client also configures itself with a default class B subnet mask of 255.255.0.0. A client uses the self-configured IP address until a DHCP server becomes available. The APIPA service also checks regularly for the presence of a DHCP server (every five minutes, according to Microsoft). If it detects a DHCP server on the network, APIPA stops, and the DHCP server replaces the APIPA networking addresses with dynamically assigned addresses.

13. DHCP scopes and leases A scope is a range of IP addresses that a DHCP server allocates to clients, along with associated IP configuration settings known as DHCP options. Along with scope, you also need to define a lease period. A long lease period means that the client does not have to renew the lease as frequently, but the DHCP server’s pool of IP addresses is not replenished.

14. DHCP options Typical DHCP options include: The default gateway The IP address of DNS servers The DNS suffix (domain name) to be used by the client Other useful server options, such as time synchronisation (NTP), file transfer (TFTP), or VoIP proxy

15. DHCP reservation is a feature in the DHCP server that allows the DHCP administrators to reserve one or more IP addresses for particular mission-critical computers only. DHCP reservations In order to configure DHCP reservation, the administrators are required to know the physical addresses ( MAC addresses) of the target computers for which the particular IP addresses are to be reserved. Once the MAC addresses are known, the administrators can then reserve the appropriate IP addresses by mapping them with the MAC addresses.

16. For example, if computer A is playing the role of a print server, and has MAC address of 00:A1:FB:12:45:4C and you want that the computer should always get 192.168.0.7 as its IP address, you can map the MAC address of the computer A with the IP address to configure reservation. When an IP address is reserved for a particular computer, the IP address remains in the DHCP address pool, even if it is the only address available for the assignment and any other client computer is requesting for the address.

17. Network Time Protocol (NTP) Many applications on networks are time dependent and time critical (such as authentication and security mechanisms, scheduling applications, or backup software). Network Time Protocol (NTP) provides a channel of transport through which to synchronise these time- dependent applications. NTP works over UDP on Port 123