Free CCNA | Static Routing | Day 11 (part 2) | CCNA 200-301 Complete Course

Static Routing

Static routes allow routers to reach networks that are not directly connected. They are configured manually and can also be used to create default routes.

Connected and local routes

Configuring an IP address on an enabled router interface automatically adds two routes:

• A connected route to the network attached to the interface.
• A local route to the interface’s exact IP address, represented as a /32.

These routes do not tell a router how to reach remote networks. If a packet’s destination matches no route in the routing table, the router drops it. In the examples, R2, R3, and R4 each have one connected and one local route per active interface.

Default gateways and packet forwarding

End hosts can communicate directly with devices on their own subnet. To reach destinations outside that subnet, they send traffic to a default gateway—the router that serves as their default path.

A host’s default route is 0.0.0.0/0. Because it matches every IPv4 address, it is the least-specific route and is used only when no more-specific route matches.

When PC1 sends traffic to PC4:

• The packet’s source and destination IP addresses remain those of PC1 and PC4 throughout the journey.
• The destination MAC address changes at each link to identify the next device that will receive the frame.
• PC1 sends the frame to its default gateway, R1. Each router removes the incoming Layer 2 frame, checks the destination IP against its routing table, and re-encapsulates the packet for the next hop.

Planning routes for two-way communication

To let PC1 (192.168.1.10) and PC4 (192.168.4.10) communicate along the path R1 → R3 → R4, each router on the path needs routes to the endpoint networks: 192.168.1.0/24 and 192.168.4.0/24.

R1 already has a connected route to PC1’s network, and R4 has a connected route to PC4’s network. The remaining routes must be configured manually:

• R1: 192.168.4.0/24 via R3 at 192.168.13.3
• R3: 192.168.1.0/24 via R1 at 192.168.13.1; 192.168.4.0/24 via R4 at 192.168.34.4
• R4: 192.168.1.0/24 via R3 at 192.168.34.3

Routes are needed in both directions. Without return routes, the destination may receive a packet but be unable to send a reply. Routers do not need routes to every intermediate network; they need to know the next hop toward the destination network.

Configuring static routes

The usual Cisco command format is:

ip route <destination-network> <subnet-mask> <next-hop-IP>

For the demonstrated path:

R1: ip route 192.168.4.0 255.255.255.0 192.168.13.3
R3: ip route 192.168.1.0 255.255.255.0 192.168.13.1
R3: ip route 192.168.4.0 255.255.255.0 192.168.34.4
R4: ip route 192.168.1.0 255.255.255.0 192.168.34.3

Static routes appear in the routing table with the code S. In the example, a successful ping from PC1 to PC4 confirms two-way reachability.

Static-route interface options

A static route can specify the next-hop IP, the exit interface, or both.

Using only an exit interface:

ip route 192.168.1.0 255.255.255.0 g0/0

Using both an exit interface and a next-hop IP:

ip route 192.168.4.0 255.255.255.0 g0/1 192.168.24.4

When only the exit interface is specified, the route may appear in the routing table as “directly connected,” even though the destination network is not physically connected to the router. This method relies on Proxy ARP. The instructor recommends knowing all three options and typically uses the next-hop-only form.

Default routes on routers

A router default route uses the ip route command with the destination network and mask both set to zero:

ip route 0.0.0.0 0.0.0.0 <next-hop-IP>

It forwards traffic when no more-specific route matches. One common use is directing traffic for external destinations toward the Internet while more-specific routes handle internal networks.

Cisco routing-table output may identify the selected default route as the gateway of last resort. An asterisk marks a route as a candidate default.

Quiz takeaways

• A valid default route uses 0.0.0.0 0.0.0.0. Cisco static-route commands use a dotted-decimal subnet mask rather than slash-prefix notation.
• To forward to an IP address using a default route, a router sends the packet to that route’s next hop and uses the interface connected to the next hop’s network.
• For traffic routed through R1 → R2 → R4, the routers need routes for both endpoint networks, with each next hop pointing to the adjacent router.
• A route marked S that says “directly connected” can be a static route configured with only an exit interface.
• A router needs static routes for remote destination networks not already covered by its connected routes or a default route.

Speakers and sources

• Jeremy (video instructor/narrator): Explains routing concepts, demonstrates configurations, and presents the quiz.
• Other featured sources: Router and host configurations, routing-table output, network diagrams, and quiz questions. No additional speakers are identifiable in the subtitles.