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DEMO: Routing Table

Routers use routing tables to determine the best next hop for each packet based on its destination IP address, forwarding traffic hop by hop until it reaches its target network. This content examines how routing tables work and demonstrates how to view them on both a Windows machine and a Layer 3 switch.

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About this video

Routing tables are the decision-making foundation of how routers move data across networks. When a packet arrives at a router, the device examines the destination IP address and compares it against its routing table to determine the optimal next hop. That packet is then forwarded to the next router, which performs the same lookup, and this hop-by-hop process continues until a router identifies the destination as a directly connected network and delivers the packet to its final target. Understanding this process is essential to grasping how traffic flows through any IP-based network infrastructure. To ground this concept in real-world tools, the content demonstrates how to view routing tables on two different devices. On a Windows machine, the route print command displays both IPv4 and IPv6 routing tables, showing the entries the operating system uses to make local forwarding decisions. On a Layer 3 switch — a device that combines switching with routing capabilities — the show ip route command reveals the full routing table the device maintains. Examining both side by side reinforces how routing table logic is consistent across different types of network-aware devices, from end hosts to dedicated routing hardware.

What you'll learn

What's covered

How Routers Use Routing Tables

Aligned to

CompTIA Network+
2.1 Explain characteristics of routing technologies.
Cisco CCNA
3.1 Interpret the components of routing table
3.2 Determine how a router makes a forwarding decision by default
1.10 Verify IP parameters for Client OS
Cisco CCST Networking
4.4 Explain basic routing concepts
5.5 Run basic show commands on a Cisco network device
5.3 Run basic diagnostic commands and interpret the results
CompTIA A+ Core 2
1.2 Given a scenario, use the appropriate Microsoft command-line tool.

Key terms

Router
A network device that forwards data packets between networks based on IP addresses.
Packet
A unit of data formatted for transmission over a network, containing a header, payload, and sometimes a trailer.
IP Address
A numerical label assigned to each device connected to a network that uses the Internet Protocol.
Layer 3
The Network layer of the OSI model, responsible for logical addressing and routing packets between networks.
Routing Table
A database stored in a router that lists known network destinations, the metric (cost) to reach them, and the next-hop address or outgoing interface to forward packets toward those destinations. Routers consult this table for every packet they forward.
Next Hop
The IP address of the immediately adjacent router that a packet is forwarded to on the way toward its final destination. A router's routing table entry for each network destination includes the next-hop address so the router knows where to send the packet.

Transcript

Routers make a determination of where to route this information, where to route these packets, by using a routing table. Each one of these routers has its own routing table, and within this routing table it specifies information that gets it to the next hop.

As information comes into this router, that router is going to look at the destination IP address, where that packet needs to go to. It's going to cross reference that with the router table and determine what the next hop is. It gets to the next router, and that router does the same thing: it takes a look at that packet, looks at the destination IP address, and determines what the next best hop is. And then this router takes a look at its routing table, realizes that that's a directly connected network, and I'm going to send it into that network so it can get to that server.

Viewing the routing table on Windows

I thought it'd be good just to take a glimpse into what these routing tables look like. I've got a Windows machine here. I'm going to open up a command window just by hitting the start button and typing in cmd. I'll hit enter, and all I need to do is a route print. What it's going to do is print out the routing tables. So here we see the IP version 6 routing tables and everything that's in the IP version 6 routing tables, and here we have the IP version 4 routing tables and everything in the IP version 4 routing table.

Viewing the routing table on a layer 3 switch

The other thing I did is I remoted into a router. It's actually a layer 3 switch, but for the purposes of this we're just going to call this a router right now. It does routing, it has routing capabilities. It's a switch that has extra capabilities, so it's a layer three switch.

What we see right here is the routing table. I did the show ip route to bring this up, and it's showing all of the routing tables.

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