# Subnetting for the Broadcast, Video and Audio Systems Engineer, Part II

For more background, read Part I

IP addresses are represented as “human readable” dotted decimal numbers.  They also can be represented as hexadecimal numbers.

Hexadecimal numbers are normally prefixed 0x followed by the hexadecimal number. Hex numbers range from decimal equivalents of 0 –15, representing 16 possible values. Hex numbers above 9 are assigned figures of A through F, where A is 10 and F is 15, etc.

A binary number of 1001 is equal to 9 in both decimal and hexadecimal.  The most significant binary digit (bit) has a weight of 8, the least has a weight of 1, therefore 9. 1010, then, would be 10 in decimal and A in Hex. These two Hex numbers would properly be shown as 0x9 and 0xA, respectively. 1111 in binary is equal to 0xF, and 15 decimal.

Two binary 4-bit words can be represented by two Hex characters. Binary 11111111 equals 0xFF or 255 decimal. Binary 11111110 is 0xFE or 254 decimal. A string of sixteen ones in binary (2^16) is 0xFFFF in Hex.  In decimal, that’s 65,536.

There are two IP addressing schemes.  The classical form is IPv4, consisting of four octets (so named because they each have eight binary data bits), each separated by a period. An example might be 192.168.2.34. This is called “dotted decimal format.” Four octets make 32 data bits to an IPv4 address.

IPv4 has limited expansion capability because more IP addresses are needed than can be had with 32 bits. Thus, IPv6 was developed with address space (I have heard), is sufficient to count all the stars in the known universe, with room left over. The total number of available addresses is 2128 or approximately 3.4 x 1038. With 2^128 available addresses, an IPv6 address utilizes a 128 bit address space. It’s formatted as eight groups of four hexadecimal digits separated by colons, such as 2001:0BD7:BC10:EF01:0000:0000:0000:0000. Sometimes there’s a double colon in the middle. Each of the eight groups is a 16 bit number in binary.

For the foreseeable future, IPv4 will be the protocol in broadcast and video production facilities.

There are three classes of IP addresses called Class A, Class B, and Class C.  There are two additional reserved classes, D and E, which are not part of this discussion.  The first few bits of the first octet of an IP address defines the IP address class:

 Click on the Image to Enlarge

The first octet is always part of the Network address.

Class A addresses start with binary 0. The first octet ranges from binary 00000000 to 01111110, or 0 to 126 in decimal.  The 127 address space (01111111) is reserved for loopback testing.  Addresses in this range may not be assigned to a network.

Class B addresses start with binary 10. The first octet may range from binary 10000000 to 10111111, or 128 – 191 decimal.

Class C addresses start with binary 110. The first octet may range from binary 11000000 to 11011111, or 192 – 223 decimal.

Each class of IP addresses includes blocks of addresses for use on the public Internet and blocks for private use.  Private addresses will not be routed on the public Internet.  The ranges of public IP addresses are:

 Class Public IP Ranges A 1.0.0.0    to 9.255.255.255 11.0.0.0 to 126.255.255.255 B 128.0.0.0 to 172.15.255.255 172.32.0.0 to 191.255.255.255 C 192.0.0.0 to 192.167.255.255 192.169.0.0 to 223.255.255.255

Table 6

These addresses are assigned via an ISP who has collaborated with an appropriate regional registry.  These registries are operated by:

·         APNIC (Asia Pacific Network Information Center)

·         ARIN (American Registry for Internet Numbers)

·         RIPE NCC (Reseaux IP Europeens Network Coordination Centre)

Because of rapid Internet growth, new technologies have been developed.  These include IPv6, Network Address Translation (NAT), and Classless Inter-Domain Routing (CIDR).  CIDR resulted from setting aside blocks of address spaces for private use, not to be used on the public Internet.  These address spaces are:

 Class Private IP Ranges A 10.0.0.0 to 10.255.255.255 B 172.16.0.0 to 172.31.255.255 C 192.168.0.0 to 192.168.255.255

Table 7

These three blocks of IP addresses are for private use.  There is one Class A network, 16 Class B Networks and 256 Class C networks within this schema.  When a device assigned a private address communicates with the public Internet, the private address is translated to a public address.  This process is via Network Address Translation, or NAT.  This service is often provided via a router.

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