How IPv4 and IPv6 addressing, CIDR prefixes, subnets, gateways, and address planning determine network reachability.
CIDR prefixes define how many address bits identify the network and how many remain available for host addressing. A subnet creates a routing and broadcast boundary within an address plan.
| Concept | Purpose |
|---|---|
| IPv4 address and prefix | Identify a host and its network range |
| IPv6 address and prefix | Identify a host and routing scope in IPv6 |
| Default gateway | Routes traffic outside the local subnet |
| VLSM | Uses different prefix lengths to match differently sized network segments |
| DHCP | Assigns addressing configuration automatically |
| APIPA / IPv4 link-local | 169.254.0.0/16 addressing often seen when DHCP configuration is unavailable |
When a host cannot reach a peer, verify its address, prefix, gateway, and route before changing DNS. Hosts that are not in the same subnet require a functioning route between their networks.