Discovery · Lesson 10

How do network addresses fit together?

A name identifies a service for people, an IP address identifies a routed destination, a port identifies an application endpoint, and a MAC address delivers the next local hop.

Several identifiers, one exchange

Network conversations use different identifiers for different decisions.

A person may start with a DNS name such as example.com. DNS can resolve that name to an IP address. Routing uses the IP address to choose a destination network, while the transport port identifies the service on that host.

At each local hop, the sender needs a next-hop link-layer address such as a MAC address. That local address can change at every router even though the end-to-end destination IP remains the routing target.

Do not treat every address as the same kind of identity.DNS names help humans and applications identify services; IP addresses support routing; ports select services; MAC addresses deliver frames across one local link.

Build the model

Four addressing roles

01

Name

DNS provides a human-friendly label that can resolve to one or more addresses.

02

IP address

IPv4 or IPv6 identifies the routed destination and its network prefix.

03

Port

A transport port selects the service or conversation endpoint on a host.

04

MAC address

A link-layer address identifies the next local receiver for a frame.

Follow the request

Each layer answers a different question

The identifiers cooperate but are not interchangeable. DNS can change its answer, routing can choose a different path, and the local MAC destination can change at every hop.

A request moves from a DNS name to an IP address, a transport port, a next-hop MAC address, and a local Ethernet or Wi-Fi frame.
Names, IP addresses, ports, and MAC addresses serve different decisions in one exchange.

Knowledge check

Test your addressing model

Answer six questions.

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