Critical Network Services: DNS, DHCP and NAT

This reference covers three critical network services that underpin almost every IP network: DHCP (automatic IP address assignment), NAT (Network Address Translation, allowing private networks to reach and be reached from the public internet), and DNS (translating human-readable names into IP addresses). The material builds a complete working lab network step by step, using Cisco routers and Ubuntu Linux servers virtualized inside Cisco Modeling Labs (CML), progressing from basic IP assignment to a fully routed, NAT'd, and name-resolved infrastructure.

This module covers IP address assignment using DHCP, the Dynamic Host Configuration Protocol (RFC 2131). The lab environment builds toward a complete working network infrastructure, starting with a single DHCP-enabled LAN and expanding to a multi-LAN topology using DHCP relay agents.

Manually assigning an IP address to every device that connects to a network — including mobile devices — is impractical. It requires maintaining a running list of already-assigned addresses and manually releasing them when devices leave the network. DHCP automates this entire process.