What is the difference between static and dynamic routing?
Static routes are entered by hand and never change unless an admin edits them. Dynamic routing uses protocols like OSPF and BGP so routers learn routes from each other and adapt automatically when links fail.
Explain it simply
Static routing is a printed bus timetable pasted on the wall: simple and reliable until a road is closed. Dynamic routing is a live maps app that reroutes you the moment it hears about a jam.
Example
Static (Linux):
ip route add 10.20.0.0/16 via 192.168.1.1
Static (Cisco style):
ip route 10.20.0.0 255.255.0.0 192.168.1.1
Dynamic: routers run OSPF / RIP / BGP, exchange updates,
and recompute paths when a link goes down.Static fits small, stable networks: a home router's default route to the ISP, or a branch office with one exit. It uses no bandwidth or CPU for updates and is predictable.
Dynamic suits large networks with many paths. Trade-offs are protocol overhead and more complexity, but failures heal without human help. Many networks mix both: a static default route pointing outward, dynamic routing inside.
A static route has an important weakness: if the next hop dies, the route stays in the table unless it is tied to a health check, and traffic is lost.
What to say in the interview
"Static routing is manual, simple and predictable but does not adapt. Dynamic routing learns and updates routes automatically using protocols, at the cost of overhead and complexity. Small stable networks use static; larger or redundant networks use dynamic."
Common mistakes
- Saying static routing is always worse. It is the right tool for stub networks.