Static Versus Dynamic Routing
By Stephen Bucaro
Routers direct traffic between networks or subnetworks, for this they operate at Layer 3, the network layer,
of the OSI Model. Routers don't track individual computers, but they contain a routing table and other
information which allows them identify the best path to take and transporting a packet to get to its destination.
Routing can be either static or dynamic. With static routing a network administrator manually creates the
router's routing table. The static routes do not change unless the network administrator updates them.
The algorithms used with static routing are simple and work very efficiently in uncomplicated networks
where traffic is relatively predictable.
With dynamic routing the router identifies which networks are directly connected to the device. Then they
use routing protocols like RIP, RIP2, EIGRP, OSPF, or BGP to advertise those destinations to other routers,
to learn about the networks connected to other routers, and the best path to take to transport a packet
to those networks.
If a change has occurred in the network, dynamic routers will send new routing update messages to each
other. Each time a router forwards a packet to the next router, it's called a "hop". Each time a hop occurs
a dynamic router will store that information and communicate it to other routers. This allows a dynamic router
to determine which route to destination network has the least hops.
Dynamic routing protocols also record the time it takes for a packet to travel between routers, and will
communicate that information to other routers. The number of hops along with the travel between routers
allows the router to determine the "best" route for a packet to take to reach a destination network.
In a large network with heavy and constantly changing traffic, dynamic routers will be sending a high number
of update messages to each other, and each router will be constantly updating their routing tables. This
creates a lot of overhead as compared to static routing. Even when you're using a dynamic routers, there
are cases where setting a static route is advantageous. The static route will be used over the dynamic route.
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