Static routing uses routes manually entered and maintained by a network administrator, whereas dynamic routing uses routing protocols to discover routes and update them automatically. Static routing offers simplicity and control; dynamic routing provides adaptability and scalability.
How the Routing Methods Work
A router stores possible destinations in a routing table. When a packet arrives, the router reads its destination IP address, consults this table, and selects the appropriate next hop.
With static routing, an administrator specifies each route. If a connection fails or the network topology changes, the route remains unchanged until the administrator edits it. This is suitable for small, stable networks or a fixed route leading out of a network.
With dynamic routing, routers exchange information through a routing protocol, such as OSPF. The protocol applies a routing metric, which may consider factors such as cost, bandwidth, or path length, to select an appropriate route. If the topology changes, routers can recalculate their routing tables.
| Factor | Static routing | Dynamic routing |
|---|---|---|
| Configuration | Routes are entered manually | Routes are learned through a routing protocol |
| Response to failure | Requires administrator intervention | Can automatically find an alternative route |
| Processing and traffic overhead | Low | Higher because routers process and exchange routing information |
| Scalability | Poor for large or frequently changing networks | Suitable for large, complex networks |
| Control | Administrator determines the exact route | Protocol selects routes using its metric |
| Risk | Human configuration errors may persist | Incorrect updates or protocol attacks may affect several routers |
A common misconception is that dynamic routing always selects the physically shortest route. It selects the route judged best according to the protocol's metric, which may not correspond to physical distance.
Exam Technique
For an IB compare question, give linked differences: state how both methods handle the same factor, such as route updates, overhead, or scalability. For a scenario-based question, justify the choice: static routing suits a small stable network, while dynamic routing suits a large network that requires automatic recovery after failures.
