Saturday, March 24, 2012

Static IP, Bootstrap IP, Auto IP and DHCP

Static IP address:

      The simplest (but not always the easiest) method is to assign a static IP address. You need to set the following parameters in the Network section of the WEB UI of the device:
  • IP address
  • netmask
  • gateway
  • primary DNS server
  • secondary (backup) DNS server
The first two (bold) parameters are the minimum for communication within a LAN. If the device needs an access to the outside world, the gateway must be configured as well. If you are using name addresses, one or better both DNS servers must be configured.

Dynamic IP addess Methods(  Bootp, DHCP, Auto IP):
     
 Bootp:
The Bootstrap Protocol allows a host to configure IP  itself dynamically at boot time.
This protocol is will obtain only the IP address, netmask and gateway.

This protocol provides 3 services:
  • IP address assignment.
  • Detection of the IP address for a serving machine.
  • The name of a file to be loaded and executed by the client machine.
 Bootp  is minimal DHCP cleint for obtaining the dynamic IP address.

DHCP:
  With DHCP typically all the above network parameters (IP address, netmask, gateway, DNS servers) are set, whereas BOOTP can set only the IP address and gateway address.



    DHCP introduces a small change in terminology intended to clarify the meaning of one of the fields. What was the "vendor extensions" field in BOOTP has been re-named the "options" field in DHCP. Similarly, the tagged data items that were used inside the BOOTP "vendor extensions" field, which were formerly referred to as "vendor extensions," are now termed simply "options."
        Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default route and routing prefix. DHCP eliminates the manual task by a network administrator. It also provides a central database of devices that are connected to the network and eliminates duplicate resource assignments.
        In addition to IP addresses, DHCP also provides other configuration information, particularly the IP addresses of local Domain Name Server (DNS), network boot servers, or other service hosts

Comparison of Bootp and DHCP:

          BOOTP                                           DHCP
*Designed prior to DHCP. *Designed after BOOTP.
*Intended to configure diskless workstations
with limited  boot capabilities.

*Intended to configure frequently relocated networked computers (such as portables) that have local hard drives and full boot capabilities.
*Dynamic BOOTP has a default 30-day expiration on IP   address leases. *DHCP has a default eight-day expiration on
   IP address leases.
*Supports a limited number of client configuration parameters called vendor extensions. *Supports a larger and extensible set of client  configuration parameters called options.




*Describes a two-phase bootstrap configuration process, as follows:
  • Clients contact BOOTP servers to perform address determination and boot file name selection.
  • Clients contact Trivial File Transfer Protocol (TFTP) servers to perform file transfer of their boot image.
*Describes a single-phase boot configuration process whereby a DHCP client negotiates with a DHCP server to determine its IP address and obtain any other initial configuration details it needs for network operation.
*BOOTP clients do not rebind or renew configuration with the BOOTP server except when the system restarts. *DHCP clients do not require a system restart to rebind or renew configuration with the DHCP server. Instead, clients automatically enter a rebinding state at set timed intervals to renew their leased address allocation with the DHCP server. This process occurs in the background and is transparent to the user.
  

AutoIP:

Automatically assigns a free IP address in the network 169.254.0.0/16. It sets the IP address and the netmask (always 255.255.0.0). Gateway address and DNS address are left intact.
This is the last method used if all the above methods  like Bootp and DHCP fails. Auto IP will be activated automatically if IP address is not obtained with help of Bootp and DHCP.

Selecting specific IP methods like Static IP, Bootp, DHCP and AUTO IP.

Each of the above methods can be enabled or disabled. By default all are enabled. A method is disabled by setting a specific bit in the third field of the IP address:
  • “0.0.1.0” to disable AutoIP
  • “0.0.2.0” to disable DHCP
  • “0.0.4.0” to disable BOOTP
  • “0.0.8.0” to disable IPzator
Examples:
  • “0.0.3.0” disables AutoIP and DHCP
  • “0.0.11.0” disables all but BOOTP
ATTENTION: “0.0.15.0” disables all discovery functions which locks you out unless you reset the device to factory defaults by pressing the reset button for about 10 seconds.