Static Routing- When it comes to routing, there are two options that can be done which are dynamic or static routing. Each has their own pros and cons, let’s break it down. Static routes are routes that are manually installed in the routing table by an IT member. These routes are “dumb” routes meaning that they only know the destination network, next hop address or outgoing interface. After that, there is nothing else to it. As you can see, if something were to happen, like a link to the path to the destination goes down the route will remain in the table but fail to reach its destination. If there is a problem in the route, it cannot be fixed until an IT member fixes it. As you can tell, this might be manageable for small companies or SOHO environments but lacks scalability for a growing or medium to large companies.
Dynamic Routing- When it comes to medium to larger companies, dynamic routing just makes so much more sense. When a router is using one of the various routing protocols, after the initial set up configuration the routing protocols handle the heavy lifting. In dynamic routing, routers keep in communication with each other whether they are using hello packets, or sending each other routing tables. In dynamic routing, the routers all share information with each other whether it’s only their neighbor or the whole routing domain area. In dynamic routing, there are timers to detect possible failure of routers or links connections, and the best part of all is that most of them have backup plans for when something bad does happen. So if a link fails somewhere, the other routers will know about it and use the already backup path or calculate the new best path depending on what algorithm is used. The algorithms used differ from protocol to protocol, and organizations can pick whichever one suits their needs. On top of having backup paths during topology changes, when neighbor adjacencies fail and updates from neighboring routers indicate unreachability any route connected to that adjacency is removed from the routing table. This allows an administrator to add a floating static route to provide even more redundancy. Dynamic routes also determine the best paths by having “metrics” which can be based on bandwidth, delay, cost, and hop count (protocols like BGP use “attributes” instead).
Dynamic routes can either be internal or external. An internal routing protocol is called “IGP” which stands for Interior Gateway Protocol. An external routing protocol is called “EGP” which stands for Exterior Gateway Protocol. IGP is used to route packets within an AS (Autonomous System) and EGP is used to route packets between AS’s. An autonomous system is a collection of routers and networks that belong to a single entity or an administrative domain. So think of it like a CVS brand and their network across all their stores, and corporate offices that are under one entity/organization called CVS.
Dynamic and static routes both have their pros and cons and serve their purposes. In a lot of environments you will find that they have a combination of both. Maybe the dynamic route figured out everything but the default route, so they use a static default route. If a company desires a high availability they can also do a dynamic routing protocol along with a floating static route. A company like CVS might use OSPF internally for automatic failover, but have a static route to their ISP, and a floating static route as a backup to the most important routes.
Static Routes Pros
- Full Control and Predictability
- Low Overhead (Since these routes do not converge when something changes, it uses a lot less CPU, memory, or bandwidth than a dynamic routing protocol)
- Simple to configure
Static Routes Cons
- No scalability (it’s tedious to configure and manage 500+ routes)
- No automatic failover or backups in response to topology changes
- A route can stay in the routing table even if the path doesn’t reach the destination
- Needs manual fixes to failures
Dynamic Routes Pros
- Faster convergence than static routes without manual configuration (not including initial configs)
- Routers communicate with each other
- Automatic route learning (routing tables are populated without manual submissions)
- There are backup routes, or path recalculations when topology changes
- Uses different metrics to determine best path
- Supports load balancing
- Allows for scalability
Dynamic Routes Cons
- Increases processing overhead (CPU, memory, bandwidth)
- Can introduce security risks
- More complex
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