DHCP/Bootp Operation


DHCP/Bootp is used to download configuration data from a DHCP or Bootp server respectively to the Hub.

Bootp: -- A Bootp server requires some configuration. It allows a device to obtain its configuration information, such as the IP Address and Subnet Mask, in one message, reducing the demand on the network. The Bootp protocol is designed for a network in which each host has a permanent network connection.

DHCP: -- The Dynamic Host Configuration Protocol (DHCP) manages the allocation of TCP/IP configuration information by automatically assigning IP addresses. With DHCP you can configure the hub to automatically retrieve the IP address with no configuration required on either the hub or the DHCP server. In dynamic mode, the address is used by the device for a specified period of time. The time period depends on the situation; one device may only need the address for an hour, while another device may use the same address for several days. DHCP is more suitable in environments where the number of IP addresses needed exceeds the number available. It also allows a device to obtain its configuration information, such as the IP Address and Subnet Mask, in one message, reducing the demand on the network.

Note: The HP J3288A Hub-12 and HP J3289A Hub-24 are compatible with both DHCP and Bootp servers

The DHCP/Bootp Process

Whenever the IP Config parameter in the hub is configured to DHCP/Bootp (the default), or when the hub is rebooted with this configuration:

  1. DHCP/Bootp requests are automatically broadcast on the local network. (The hub sends one type of request which either a DHCP or Bootp server can process.)
  2. When a DHCP or Bootp server receives the request, it replies with an automatically generated IP address and subnet mask for the hub. The hub also receives an IP Gateway address if the server has been configured to provide one.

In the case of Bootp, the server must first be configured with an entry that has the MAC address of the hub. (The hub properly handles replies from either type of server. If multiple replies are returned, the hub tries to use the first DHCP reply.) If the hub is initially configured for DHCP/Bootp operation (the default), or if it is rebooted with this configuration, it immediately begins sending request packets on the network. If the hub does not receive a reply to its DHCP/Bootp requests, it continues to periodically send request packets, but with decreasing frequency. Thus, if a DHCP or Bootp server is not available or accessible to the hub when DHCP/Bootp is first configured, the hub may not immediately receive the desired configuration.

DHCP Operation: -- A significant difference between a DHCP configuration and a Bootp configuration is that an IP address assignment from a DHCP server is automatic, requiring no configuration of the DHCP server. Using that automatic feature, though, the address is temporarily leased. Periodically the hub may be required to renew its lease of the IP configuration. Thus, the IP addressing provided by the server may be different each time the hub reboots or renews its configuration from the server. However, you can fix the address assignment for the hub by doing either of the following:

For more information on either of these procedures, refer to the documentation provided with the DHCP server.

Bootp Operation: -- When a Bootp server receives a request it searches its Bootp database for a record entry that matches the MAC address in the Bootp request from the hub. If a match is found, the configuration data in the associated database record is returned to the hub. For most Unix systems, the Bootp database is contained in the /etc/bootptab file. In contrast to DHCP operation, Bootp configurations are always the same for each receiving device. That is, the Bootp server replies to a request with a configuration previously stored in the server and designated for the requesting device.

You can configure DHCP/Bootp from either the web browser interface or the hub console interface.

Return to IP Configuration

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