Static & Dynamic Routing (HL)
What is Routing?
Routing is the process of determining the best path for data packets to travel across a network.
There are two main types of routing: static routing and dynamic routing, each with different advantages and use cases.
Static Routing
Static routing uses routes that an administrator types in by hand; they stay the same until someone edits them.
| Feature | Explanation |
|---|---|
| Configuration | Routes are entered manually (destination network → next hop).
Scenario: In a small shop with one router, the admin adds a single default route to the ISP and a static route to a back-office subnet.
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| Maintenance | Any network change requires editing the routes.
Scenario: If the file server moves to a new subnet, the admin must update the static route or devices can’t reach it.
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| Complexity | Low - no routing algorithms to tune.
Scenario: A classroom lab with one uplink can be set up in minutes with a default route.
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| Resource Usage | Very low CPU/RAM - router just follows the table.
Scenario: Works well on low-end branch routers or embedded gateways.
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| Path Update | No automatic change on failure.
Scenario: If the link to the printer VLAN goes down, printing stops until an admin edits the route to use another link.
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| Scalability | Poor - route count and admin work grow quickly as the network grows.
Scenario: Adding new departments means adding/maintaining more static entries on multiple routers.
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| Network Size | Best for small, stable LANs.
Scenario:Home office or a single-floor retail store where the topology rarely changes.
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Why it's used in LANs: In small LANs - like a school IT lab or a retail store - the network structure rarely changes. A network administrator can manually configure routes for each switch or router. Since the traffic pattern is predictable, static routing is fast, simple, and requires little processing power.
Example: In a retail store LAN, the route from the checkout system to the inventory server is fixed. A static rule ensures packets always follow the same path. This avoids unexpected delays, but if a link fails, the route must be manually changed.
Dynamic Routing
Dynamic routing lets routers learn paths from each other and pick the best route based on current network conditions.
| Feature | Explanation |
|---|---|
| Configuration | Light initial setup - enable routing on the right interfaces; routers discover neighbours and exchange routes.
Scenario: A campus core and building routers auto-learn each other’s subnets.
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| Maintenance | Self-updating - new links and subnet moves are learned automatically.
Scenario: IT adds a new Wi-Fi VLAN; routes appear across the LAN without manual edits.
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| Complexity | Higher - must understand basic routing behaviour and design rules.
Scenario: The network team plans which interfaces participate and checks that learnt routes look sensible.
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| Resource Usage | Moderate - routers exchange updates and compute paths.
Scenario: During a change window, routers briefly use extra CPU to recompute best paths.
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| Path Update | Fast - routes adapt after failures or congestion.
Scenario: A fibre between buildings is cut; traffic shifts to a backup link within seconds.
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| Scalability | Excellent - new routers/links integrate with little manual work.
Scenario: A university adds a new wing; dynamic routing advertises those subnets across campus automatically.
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| Network Size | Ideal for medium/large or changing networks.
Scenario: Multi-floor offices, campuses, or ISP/access networks where devices and paths change over time.
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Why it's used in LANs: In larger LANs - such as in a university or multi-floor office - devices and links may be added, removed, or experience congestion. Dynamic routing automatically recalculates the best path as needed, without human intervention.
Example: A university LAN has routers between different departments. If the IT department router fails, the dynamic routing protocol detects this and finds an alternative route for students accessing files from the central server - all in real time.
Comparison of Static and Dynamic Routing
| Feature | Static Routing | Dynamic Routing |
|---|---|---|
| Configuration | Manual | Automatic |
| Maintenance | Manual updates needed | Updates automatically |
| Complexity | Low (easy to manage) | Higher (requires understanding of routing behaviour) |
| Resource Usage | Minimal | Moderate to high |
| Path Update | None (routes fixed) | Dynamic – adjusts to changes |
| Scalability | Limited | Highly scalable |
| Network Size | Small networks | Large, complex networks |
Where Are Static and Dynamic Routing Used?
Static Routing
- Small businesses with fixed network paths.
- Home routers with limited connections.
- Environments with strict security policies.
Dynamic Routing
- Large organisations needing automated adaptation.
- ISPs and telecommunications networks.
- Cloud-based services and multi-branch enterprises.
Why is Routing Important?
- Efficient Packet Delivery: Routing ensures data gets to its destination via the best path.
- Supports Growth: Routing strategies make expanding networks possible.
- Reduces Downtime: Dynamic routing can adapt to avoid broken links.
- Improves Performance: Routes can be optimised to prevent congestion.
Key Takeaways
- Routing determines the path that packets take to reach their destination.
- Static routing uses manually configured paths – it's simple but inflexible.
- Dynamic routing uses algorithms to adjust paths automatically based on network conditions.
- Choosing between them depends on network size, scalability, maintenance, and adaptability.