Learning Objectives
- Understand what static routing is and when to use it
- Learn how to configure static routes on a router
- Interpret routing table entries
- Analyze troubleshooting scenarios
What is Static Routing?
A static route is a manually configured entry in a router's routing table that tells the router how to reach a specific destination network. Unlike dynamic routing protocols, static routes do not change unless a network administrator updates them. This makes them predictable, secure, and lightweight — but also brittle when network topologies change.
Static routing is most appropriate for small networks, stub networks (networks with only one path out), or as a failsafe backup to a dynamic routing protocol. Many home routers use a single default static route — 0.0.0.0/0 pointing to the ISP gateway — as their only route.
How Static Routes Work
When a router receives a packet destined for a network not directly connected, it checks its routing table. If a matching static route exists, the router forwards the packet to the specified next-hop IP address or out the specified exit interface. If no match exists, the packet is dropped and an ICMP Destination Unreachable message is sent back.
The basic syntax on Cisco IOS is:
ip route <destination-network> <subnet-mask> <next-hop|exit-interface>
For example, ip route 10.1.2.0 255.255.255.0 192.168.1.1 tells the router: "To reach 10.1.2.0/24, send packets to 192.168.1.1."
Static Route Topology
In this topology, R1 needs a static route to reach 10.1.3.0/24 behind R3. R1's next hop is R2, and R2's next hop is R3.
Configuring Static Routes
On R1, to reach the 10.1.3.0/24 network at the far end:
R1(config)# ip route 10.1.3.0 255.255.255.0 10.1.12.2
This tells R1: "For 10.1.3.0/24, send to 10.1.12.2 (R2's interface)." R2 needs a return route:
R2(config)# ip route 10.1.1.0 255.255.255.0 10.1.12.1
For R2 to forward traffic toward 10.1.3.0/24, it also needs:
R2(config)# ip route 10.1.3.0 255.255.255.0 10.1.23.2
The router's routing table shows these as entries prefixed with S for static:
R1# show ip route
S 10.1.3.0/24 [1/0] via 10.1.12.2
Configure a Static Route
Build a static route command to reach a remote network.
ip route {network} {mask} {next_hop}Default Routes
A special type of static route is the default route — the "catch-all" entry used when no more specific route matches:
ip route 0.0.0.0 0.0.0.0 203.0.113.1
This says: "For all traffic, send to 203.0.113.1." Default routes are essential for internet access. Every ISP customer has one pointing toward the ISP gateway.
What is the minimum number of static routes needed for three routers in a chain (R1—R2—R3) so that every router can reach every subnet?
Advantages and Limitations
| Pros | Cons | |------|------| | No CPU overhead from routing protocols | Must be manually updated on topology changes | | More secure — no advertisements | Does not scale beyond small networks | | Predictable and easy to debug | Prone to human error | | Works in any network | No automatic failover |
What does the administrative distance [1/0] mean in a static route entry?
A stub network with one exit path to the internet is best served by which type of route?
Key Takeaways
- Static routes are manually configured and do not adapt to network changes
- The command format is
ip route <network> <mask> <next-hop> - Default routes (
0.0.0.0/0) act as catch-all entries for internet-bound traffic - Static routing works well for small/stub networks but does not scale
- Troubleshooting static routes involves checking routing tables and verifying next-hop reachability