About IP Addresses

To send ordinary mail to a person, you must know his or her street address. For one computer on the Internet to send data to a different computer, it must know the address of that computer. A computer address is known as an Internet Protocol (IP) address. All devices on the Internet have unique IP addresses, which enable other devices on the Internet to find and interact with them.

Fireware XTM supports both IPv4 and IPv6 addresses. IPv6 addresses are supported only when the XTM device is configured in mixed routing mode.

For more information about Fireware XTM support for IPv6, see About IPv6 Support.

IPv4 Addresses

An IPv4 address consists of four octets (8-bit binary number sequences) expressed in decimal format and separated by periods. Each number between the periods must be within the range of 0 and 255. Some examples of IPv4 addresses are:

Private Addresses and Gateways 

Many companies create private networks that have their own address space. The addresses 10.x.x.x and 192.168.x.x are reserved for private IP addresses. Computers on the Internet cannot use these addresses. If your computer is on a private network, you connect to the Internet through a gateway device that has a public IP address.

Usually, the default gateway is the router that is between your network and the Internet. After you install the XTM device on your network, it becomes the default gateway for all computers connected to its trusted or optional interfaces.

About Subnet Masks 

Because of security and performance considerations, networks are often divided into smaller portions called subnets. All devices in a subnet have similar IP addresses. For example, all devices that have IP addresses whose first three octets are 10.0.1 would belong to the same subnet.

The subnet mask for a network IP address, or netmask, is a series of bits that mask sections of the IP address that identify which parts of the IP address are for the network and which parts are for the host. A subnet mask can be written in the same way as an IP address, or in slash or CIDR notation.

IPv6 Addresses

IPv6 increases the IP address size from the 32 bits found in IPv4 to 128 bits. This allows for a more structured hierarchy in addresses, and supports a much larger total number of addresses.

IPv6 Address Format

An IPv6 address contains eight groups of 16-bit hexadecimal values, separated by colons (:). The hexadecimal digits are not case-sensitive. Some examples of IPv6 addresses are:

The first four groups of 16-bit hexadecimal values represent the network. The last four groups of 16-bit hexadecimal values are the interface ID that uniquely identifies each networked device. This value is usually derived from the MAC address of the device.

Shorten an IPv6 Address

There are two ways you can shorten the notation of an IPv6 address:

2561:1900:4545:0003:0200:F8FF:FE21:67CF

2561:1900:4545:3:200:F8FF:FE21:67CF

FE80:0000:0000:0000:2045:FAEB:33AF:8374

FE80::2045:FAEB:33AF:8374

You can use two colons (::) only once in an IPv6 address to represent adjacent groups with all zeros.

IPv6 Prefix

The IPv6 prefix indicates the subnet associated with an IPv6 address. The prefix is expressed as a slash (/) followed by the prefix size, which is a decimal number between 1 and 128. The prefix size indicates how many bits of the address make up the network identifier prefix. Examples of IPv6 prefixes are:

See Also

About Entering Addresses

About Slash Notation

About DNS (Domain Name System)

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