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Embed code for: 08.7 Private Versus Public IPv4 Addresses
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08.7 Private Versus Public IPv4 Addresses
9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/8/pages/7 1/2 Private Versus Public IPv4 Addresses Section 8: Understanding the TCP/IP Internet Layer As the Internet began to grow exponentially in the 1990s, it became clear that if the current growth trajectory continued, eventually there wouldn't be enough IP addresses for everyone that wanted one. Work began on a permanent solution, which would become IPv6, but in the interim, several other solutions were developed. These included NAT, CIDR, private IP addressing, and VLSM. Public IP Addresses Public IP addresses are required by hosts that are publicly accessible over the Internet. Internet stability depends directly on the uniqueness of publicly used network addresses. Therefore, a mechanism is needed to ensure that addresses are, in fact, unique. The allocation of IP addresses is managed by the IANA. With few exceptions, businesses and home Internet users receive their IP address assignment from their LIR, which is typically their ISP. These IP addresses are called “providerdependent” because they are linked to the ISP. If you change ISPs, you will have to readdress your Internetfacing hosts. IP Address Class Public IP Address Range A 126.96.36.199 to 188.8.131.52 184.108.40.206 to 220.127.116.11 B 18.104.22.168 to 22.214.171.124 126.96.36.199 to 188.8.131.52 C 192.0.0.0 to 184.108.40.206 220.127.116.11 to 18.104.22.168 9/11/2016 Cisco ELearning for ICND1 v2.0 https://ondemandelearning.cisco.com/ciscosc/icnd1#/sections/8/pages/7 2/2 Private IP Addresses Internet hosts require a globally unique IP address, but private hosts that are not connected to the Internet can use any valid address, as long as it is unique within the private network. However, because many private networks exist alongside public networks, deploying arbitrary IP addresses is strongly discouraged. In February of 1996, the IETF published RFC 1918, “Address Allocation for Private Internets,” to both ease the accelerating depletion of globally routable IP addresses and provide companies an alternative to using arbitrary IP addresses. Three blocks of IP addresses (one Class A network, 16 Class B networks, and 256 Class C networks) are designated for private, internal use. Addresses in these ranges are not routed on the Internet backbone. Internet routers are configured to discard private addresses. In a private intranet, these private addresses can be used instead of globally unique addresses. When a network that is using private addresses requires Internet connectivity, it is necessary to translate the private addresses to public addresses. This translation process is called NAT. A router or firewall is often the network device that performs NAT. IP Address Class Private IP Address Range IP Address Class Private IP Address Range 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 Up Next: Domain Name System