What is routing?

Routing is the process of choosing a path and forwarding data packets from a source to a destination across one or more networks.

Simply put: routing is the decision of which path to send an IP packet along so it reaches the target network.

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#Why routing is needed

If devices are located:

• in the same subnet → they communicate directly
• in different subnets → a router and routing are needed

Without routing:

• the Internet would not work
• data could not pass between networks

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#How routing works (step by step)

#1. The packet arrives at the router

A device sends a packet if it understands that the recipient is in a different network.

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#2. Analysis of the destination IP address

The router looks at:

• the destination IP address
• the network part of the address

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#3. Finding a route

The router consults the routing table, which specifies:

• which network
• through which interface
• through which next hop

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#4. Forwarding the packet further

The packet is sent:

• either directly to the target network
• or to the next router

This process repeats at every router until the packet reaches the recipient's network.

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#What routing relies on

Routing is based on:

• IP addresses
• network addresses and masks
• routing tables

A router does not look at what is inside the packet (application data); it works only with the IP header.

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#Types of routing (briefly)

#1. Static

• routes are configured manually
• simple, but inconvenient in large networks

#2. Dynamic

• routes are built automatically
• routers exchange information
• used in large and complex networks

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#What is important to remember for an interview

• routing is the network layer (L3)
• packets are routed, not frames
• the decision is made for each packet
• the router chooses the best path, not necessarily the shortest one

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#In short, for an interview

Routing is the process of choosing a route and forwarding IP packets between networks based on IP addresses and routing tables, ensuring data is delivered from source to destination.