R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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Subnetting increases the number of addresses that cannot be assigned to hosts. Therefore, using subnets
means accommodating somewhat fewer hosts
For example, a Class B network without subnetting can accommodate 1022 more hosts than the same
network subnetted into 512 subnets.
• Without subnetting—65,534 hosts (2
16
– 2). (The two deducted addresses are the broadcast
address, which has an all-one host ID, and the network address, which has an all-zero host ID.)
• With subnetting—Using the first 9 bits of the host-id for subnetting provides 512 (2
9
) subnets.
However, only 7 bits remain available for the host ID. This allows 126 (2
7
– 2) hosts in each subnet,
a total of 64,512 hosts (512 × 126).
Configuring an IP address for an interface
An interface must have an IP address to communicate with other hosts. You can either manually assign
an IP address to an interface, or configure the interface to obtain an IP address through BOOTP, DHCP,
or PPP address negotiation. If you change the way an interface obtains an IP address, the new IP address
will overwrite the previous one.
NOTE:
This chapter only covers how to assign an IP address manually. For information about how to obtain an IP
address through BOOTP or DHCP, see the chapter “DHCP overview.” For information about how to obtain
an IP address through PPP address negotiation, see the chapter “PPP configuration.”
Assigning an IP address to an interface
You can assign an interface one primary address and multiple secondary addresses.
Generally, you only need to assign the primary address to an interface. In some cases, you must assign
secondary IP addresses to the interface. For example, if the interface connects to two subnets, to enable
the firewall to communicate with all hosts on the LAN, assign a primary IP address and a secondary IP
address to the interface.
Configuration guidelines
Follow these guidelines when you assign an IP address to an interface:
• Each interface has only one primary IP address. A newly configured primary IP address overwrites
the previous one.
• You cannot assign secondary IP addresses to an interface that obtains an IP address through
BOOTP, DHCP, PPP address negotiation, or IP unnumbered.
• The primary and secondary IP addresses you assign to the interface can be located on the same
network segment, but different interfaces on your device must reside on different network segments.
• You can manually assign an IP address to an interface, or configure the interface to obtain an IP
address through BOOTP, DHCP, or PPP address negotiation. If you change the way an interface
obtains an IP address, the new IP address overwrites the previous one.
Configuration procedure
To assign an IP address to an interface: