3.3.1. IP Configuration and Addressing
💡 First Principle: IP addressing is the foundation of all network communication. Every device needs a unique, routable address; every packet needs a destination; and the server needs to know where to send traffic that isn't for its local network (the default gateway). Getting any of these wrong causes connectivity failures.
IPv4 Addressing
IPv4 addresses are 32-bit values written in dotted-decimal notation (e.g., 192.168.1.10). Key concepts:
- Subnet mask: Defines which portion of the address identifies the network vs. the host. A /24 mask (255.255.255.0) means the first 24 bits are the network; hosts can range from .1 to .254.
- Default gateway: The router address that forwards traffic to other networks. If misconfigured or absent, the server can communicate locally but cannot reach remote networks.
- MAC address: The 48-bit hardware address burned into the NIC. Used for communication within a local network segment; routers use IP, switches use MAC.
RFC 1918 Private Address Spaces — These ranges are not routable on the public Internet:
| Range | CIDR | Common Use |
|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | Large enterprises |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | Medium environments |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | Small offices, labs |
APIPA (Automatic Private IP Addressing): When a Windows host can't reach a DHCP server, it self-assigns an address in the 169.254.0.0/16 range. An APIPA address is a reliable symptom of DHCP failure. The host can communicate with other APIPA hosts on the same segment but cannot reach other networks.
Static vs. Dynamic Addressing
- Static IP: Manually configured. Used for servers, printers, and infrastructure devices that must have predictable addresses. DNS records and firewall rules depend on static addresses not changing.
- DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP address, subnet mask, default gateway, and DNS server. Used for workstations and devices that don't need fixed addresses. DHCP servers maintain a lease pool; when leases expire, addresses can be reassigned.
IPv6
IPv6 uses 128-bit addresses written in hexadecimal (e.g., 2001:db8::1). Key exam points:
- IPv6 link-local addresses start with
fe80::—automatically assigned on every interface - No broadcast in IPv6 (replaced by multicast)
- IPv6 is increasingly tested on Server+; understand that dual-stack (running IPv4 and IPv6 simultaneously) is common in modern environments
⚠️ Exam Trap: An APIPA address (169.254.x.x) does NOT mean the NIC is broken or the network cable is bad. It specifically means the DHCP client failed to get a lease. Check the DHCP server, DHCP relay agent, and network connectivity to the DHCP server.
Reflection Question: A server receives the IP address 169.254.44.12 after reboot. What does this tell you, and what is your first troubleshooting step?
