IP Addressing

• Domain 1.0 Networking concepts: use appropriate IPv4 network addressing (public vs. private, APIPA, RFC 1918, loopback/localhost, subnetting with VLSM and CIDR, and address classes A to E).
• Domain 1.0 Networking concepts: evolving use cases, including IPv6 addressing, mitigating address exhaustion, and compatibility requirements (tunneling, dual stack, NAT64).
• Domain 3.0 Network operations: implement IPv4 and IPv6 network services, including stateless address autoconfiguration (SLAAC).

• Public addresses are routable on the Internet. Private addresses (RFC 1918) are not.
• Class A private range: 10.0.0.0 through 10.255.255.255.
• Class B private range: 172.16.0.0 through 172.31.255.255.
• Class C private range: 192.168.0.0 through 192.168.255.255.
• APIPA (Automatic Private IP Addressing) range: 169.254.0.1 through 169.254.255.254. A client that cannot reach a DHCP server configures itself with an APIPA address and the default Class B mask 255.255.0.0.
• Loopback (localhost) addresses point a host at itself. 127.0.0.1 is the one you use.

Seeing 169.254.x.x on a client means DHCP did not answer. It is a symptom to troubleshoot, not an address to keep.

• The gap between 126 and 128 is the 127 loopback network.
• Class D and E have no network and host split because they are not used for ordinary host addressing.

• For a corporate network of any size, consultants use a Class A private network (10.0.0.0) because it gives the most flexibility and room to grow.
• Example: Acme Corporation has 14 departments with about 70 users each. A plan of 10.1.x.0 with a /24 mask, where x is the department's subnet number, is easy to design, install, and troubleshoot.
• Using 10.0.0.0 with a /24 mask gives 65,536 networks of 254 hosts each.
• For a home network, use a Class C private address. It is the easiest to understand and configure, and the default Class C mask gives one network with 254 hosts.
• CIDR and VLSM let you give each department or building only the number of addresses it needs, without wasting space. Chapter 8 covers the subnet math. A /24 means 24 of the 32 mask bits are turned on.

• Without IPv6 the world would run out of IPv4 addresses. IPv6 mitigates address exhaustion.
• An IPv6 address is 128 bits long and written in hexadecimal. An IPv4 address is 32 bits long and written in decimal.
• If the acronym IP is used alone, it means IPv4.
• Link-local addresses are like IPv4 APIPA addresses, but they cannot be routed at all, not even inside your organization.
• Unique local addresses are like IPv4 private addresses. They cannot be routed to the Internet, but unlike link-local they can be routed inside your organization.

Link-local: never routed. Unique local: routed inside the organization, never on the Internet.

• IPv6 has 128-bit addresses against 32-bit IPv4 addresses, so 96 more bits.
• Benefits over IPv4 include more available addresses, a simpler header, and options for authentication and other security.
• A MAC address is a 48-bit (6-byte) address physically assigned to a network interface such as a NIC. It is also called a hardware address or a burned-in address.

Match the phrase to the type: single interface is unicast, public-like is global unicast, not routed is link-local, not on the Internet but globally unique is unique local, multiple interfaces is multicast, nearest is anycast.

• Tunneling carries IPv6 traffic inside IPv4 so it can cross an IPv4-only part of the network.
• Dual stack runs IPv4 and IPv6 side by side on the same devices.
• NAT64 translates between IPv6 and IPv4 so IPv6-only hosts can reach IPv4 services.

• Hosts can use stateless address autoconfiguration (SLAAC) to obtain an IPv6 address without a DHCP server. One way to build the interface ID is EUI-64.
• EUI-64 takes the host's 48-bit MAC address and inserts FF:FE in the middle, which makes a 64-bit interface ID.
• It also inverts the 7th bit of the first byte, typically changing it from 0 to 1.

Reading an EUI-64 address backwards: drop the FF:FE and flip the 7th bit back to recover the MAC address.

• Open a command prompt (Start, type cmd, press Enter).
• Run ipconfig /all and note the addresses on your computer. On Linux or macOS the command is ifconfig.
• Open a web browser, go to whatismyipaddress.com or a similar site, and note the address shown as your public IP.
• For each address, identify the version, the class, and the type. Is it public or private? What is in use on your Internet connection?

• Cover the answer column and say each answer out loud before you check it. The Written labs visual lets you type answers and compare.

Lab 7.2 gives you the whole IPv6 type map: unicast, global unicast, link-local, unique local, multicast, anycast. Say the delivery phrase for each without looking.

• Class A is 1 to 126 (8 network bits, 24 host bits). Class B is 128 to 191 (16/16). Class C is 192 to 223 (24/8).
• Know the three private ranges: 10.0.0.0/8, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to 192.168.255.255.
• APIPA is 169.254.0.1 to 169.254.255.254 with mask 255.255.0.0.
• IPv6 exists because IPv4 addresses would run out. It is 128 bits, hexadecimal.
• Link-local cannot be routed at all. Unique local can be routed inside the organization.
• Read an EUI-64 address: FF:FE is inserted in the middle of the MAC address and the 7th bit of the first byte is inverted.
• IPv6 types: unicast is one-to-one, multicast is one-to-many, anycast is one-to-nearest. Global unicast is the public-style address, link-local starts with FE80::/10, unique local starts with FC00::/7, and loopback is ::1.
• The 127.0.0.1 loopback is for diagnostics. The whole 127.0.0.1 through 127.255.255.254 range is loopback.