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Types of Destination Networks

Routing tables map destination networks to their next-hop addresses, organizing entries into three categories: directly connected networks, remote networks, and the router's own local interface. Understanding these distinctions is foundational to how routers make forwarding decisions.

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About this video

A routing table is a list of destination networks paired with the information a router needs to forward traffic toward each one, and every entry belongs to one of three distinct categories. The first is directly connected networks, which are the networks attached directly to the router's interfaces. When an IP address is configured on an interface, the router automatically recognizes the network associated with that address and adds it to the table, marking those entries with a C. A single router can have multiple directly connected networks, one for each active interface. The second category is remote networks, which are destinations that cannot be reached without passing through at least one other router. A router does not need to know every intermediate network along the path to a remote destination — it only needs to know the next hop, the address of the neighboring router that will carry the packet closer to its target. Remote routes can be added manually or learned automatically through dynamic routing protocols such as OSPF, which continuously share routing information between routers. The third category is the router's own local interface addresses, labeled L in the routing table. These entries represent the specific IP addresses assigned to the router itself, and they exist to handle traffic directed at the device, such as management connections over SSH or network monitoring activity. Together, these three categories give administrators a clear picture of how a router understands its network environment and makes forwarding decisions.

What you'll learn

What's covered

Routing Tables Overview

Aligned to

Cisco CCNA
3.1 Interpret the components of routing table
3.2 Determine how a router makes a forwarding decision by default
1.6 Configure and verify IPv4 addressing and subnetting
CompTIA Network+
2.1 Explain characteristics of routing technologies
Cisco CCST Networking
4.4 Explain basic routing concepts

Key terms

Router
A network device that forwards data packets between networks based on IP addresses.
Routing Protocol
A protocol used by routers to communicate and share routing information to determine the best path for data.
IP Address
A numerical label assigned to each device connected to a network that uses the Internet Protocol.
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.
Directly Connected Network
A network that is physically attached to a router interface; automatically added to the routing table when an IP address is assigned to the interface.
Remote Network
A network that is not directly attached to a router and must be reached through one or more intermediate hops, learned via static configuration or a routing protocol.
Local Interface Route
A host route (typically /32) automatically added to the routing table representing the exact IP address assigned to a router's own interface, marked with the code 'L'.

Transcript

Our routing table is just a list of destination networks, so it has a list of networks and what is the next hop. There's really three different kinds of networks that we'll see within here.

Directly Connected Networks

One is a local network. Here we have a directly connected network to this router. When we have an interface on the router and we assign an IP address to it, it recognizes that that IP address that's assigned to it, there's a whole network that that's a part of. So it will recognize this network right here. It's actually connected to two other directly connected networks, this one right here and this one right here. So those are all directly connected networks.

Remote Networks

Then it also has a destination network of possibly some remote network. So here in this example right here we have a remote network that this router is going to need to know the location of. In order for it to get packets to there, then it needs to know of that remote network. So we have our directly connected networks, we have our remote networks.

There's actually two more remote networks that are here, and that's this link right here and this link right here. This router may or may not need to know about those networks right there for it to get to this final destination right here. It just needs to know about this remote network and the next hop, so it doesn't necessarily need to know about these networks right here. But in a lot of cases, for instance, if this router wants to communicate with this router, then it will probably need to know about this network right here. For the most part — there are some exceptions to that — those are remote networks.

The Local Link

So we've got directly connected networks, we've got remote networks, and we also have the machine itself. The machine itself, the local link: some traffic is actually destined for that router. It could be taking that information in, and perhaps it's some sort of management traffic to get on and SSH onto that machine, or to analyze, to do some sort of network management. It's managing those links. So there's reasons for us to communicate directly to that router. We can make a connection to the router, it has directly connected networks, and it has remote networks.

On the Router

I'm on a router here and I thought we could look at these three different types of destination networks.

First of all is that directly connected network. It's a network that's connected to this machine. This is labeled with a C. As we see here, here's one right here, so that's a C. Here's two of them right here, those are both C's, and this one. So according to this there are four directly connected networks.

The other thing that I had mentioned is that there's the local link, the local interface, and so that is the L right here. The L is the local. So we see that this is the actual IP address of this router right here, which is 10.240.0.2, and we have another one which is 10.240.2.2. So those are IP addresses that are actually assigned on the machine.

The rest of these are remote networks. So this 10.110.0 is some other network that's been actually learned. If we look at this, this is learned through OSPF. We haven't learned about how these actual routes get into here, but this is showing us that it's learned it through OSPF.

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