DHCP Overview - Network Basics

Dynamic Host Configuration Protocol supplies clients with leased network configuration. In DHCPv4, this can include an IPv4 address, subnet mask, default routers, DNS servers, lease time, and other options selected by local policy.

Clients, Servers, and Relays

A DHCP server manages scopes or address pools and lease state. The server does not need to reside on every physical segment: a DHCP relay can forward client exchanges between a subnet and a centralized server. Networks using only static configuration may not provide DHCP at all.

DHCP is an application-layer protocol carried over UDP. DHCPv4 servers normally use UDP port 67 and clients port 68.

CheckWhat does a DHCP relay enable?

Initial DHCPv4 Exchange

The common initial process is remembered as DORA:

DHCPDISCOVER: a client searches for available servers.
DHCPOFFER: a server proposes an address and options.
DHCPREQUEST: the client selects and requests an offered lease.
DHCPACK: the selected server confirms the lease and options.

Broadcast and unicast details vary with client state, relay use, and server capabilities. An offer is not yet the final usable lease; the acknowledgement completes the normal selection exchange.

CheckWhat is the normal initial DHCPv4 order?

Lease Renewal

A lease expires unless renewed. A client normally begins renewal before expiry, often first contacting the original server directly. If renewal does not succeed, it later broadens the rebinding attempt. Exact timers are supplied or derived under the protocol.

An address shown as dynamically assigned does not prove that its lease will remain forever. Record the active lease, lifetime, server, and options when troubleshooting changes.

CheckWhat happens to a DHCP address lease without successful renewal?

Inspecting the Result

After a client configures DHCP, verify all required state rather than only the address:

$ ip address show
$ ip route show
$ resolvectl status

The resolver command varies by system. Also inspect the active network manager's lease data and logs. Duplicate addresses can still occur through rogue servers, static assignments inside a pool, stale state, or manual configuration; DHCP reduces mistakes but cannot prevent every conflict by itself.

CheckWhat should be checked after a DHCP lease is accepted?

DHCPv6 and IPv6 Configuration

IPv6 hosts can use Stateless Address Autoconfiguration, DHCPv6, static configuration, or combinations. DHCPv6 does not use the IPv4 DORA exchange, and the default-router information normally comes from IPv6 Router Advertisements rather than DHCPv6.

CheckWhere does an IPv6 host normally learn its default-router information?

Summary

You can now explain how DHCPv4 leases and renews a host's network configuration.

Distinguish DHCP servers from relays and client subnets.
Follow the DISCOVER, OFFER, REQUEST, and ACK exchange.
Treat addresses and options as time-limited lease state.
Verify address, routes, DNS, and lease metadata together.
Keep DHCPv4 behavior distinct from IPv6 autoconfiguration.

Practice

In the practice terminal below: 1. Check your address: ip address show 2. Check your routes: ip route show Find the IPv4 address this container was given and its default route.

Look for inet on eth0, then a default via line.