Military Embedded Systems

Static routing vs dynamic routing on Ethernet networks


November 25, 2015

Ronen Isaac


ETHERNET EVERYWHERE BLOG: “Routing” on a network is a common term that I think almost everybody knows and understands today. Just to clarify, routing is the act of finding a path for a data packet to travel from one network to another. However did you know that there are three key elements needed to make this routing happen:

• Routing protocols, the rules that specifiy how information to be gathered and then distributes this information down the line to other devices on the network
• Routing algorithms, to determine the best choice of paths
• Routing databases to store information that the algorithm has discovered. The routing database sometimes corresponds directly to routing table entries, sometimes not.

There are two basic methods of building a routing table: Static Routing and Dynamic Routing

A static routing table is created, maintained, and updated by a network administrator, manually. A static route to every network must be configured on every router for full connectivity. This provides a granular level of control over routing and is completely manageable on smaller networks. It also allows for simple routing and network segmentation tasks such as inter-virtual local area network (VLAN) routing. This enables network segmentation to isolate certain broadcast domains, while still allowing connectivity between those subnets. Static routing can also be used for a default gateway, or “router of last resort” to tell packets without routing information “that router will give you directions on how to get where you want to go.”

However, static routing is not fault-tolerant, as any change to the routing infrastructure (such as a link going down, or a new network added) requires manual intervention. Routers operating in a purely static environment cannot seamlessly choose a better route if a link becomes unavailable. Because no information is intelligently shared between routers, some Layer 2 network switches, along with Layer 3 routers, can support static routing. Simply stated, static routing is great for networks that don’t change.

If you are building a larger or more fluid network, dynamic routing allows routers on the network to make intelligent decisions on which path is best to get data to a subnet/destination. A dynamic routing table is created, maintained, and updated by a routing protocol running on the router. Intelligent routing protocols are capable of dynamically choosing a different (or better) path when there is a change to the routing infrastructure.

In most networks, you may have multiple paths to the same destination—to get from Point A to Point D, you can go A to B to D or you could go from A to C to D. One of these paths may be more efficient than the other. Routers make the determination based on several criteria including network quality, link up/down, traffic congestion, etc. One of the key benefits of dynamic routing is “redundancy”-if one path on the network disappears (hardware failure, a broken data link), dynamic routing will tell the Layer 3 routers how to route around that path without manual intervention.

In military applications, a good example is, let’s say, that an IP-based computer needs to send data from its hard drive to a central command center. In this scenario, data communication is usually achieved over a wireless mesh network. However, this network needs to be fully redundant and was architected with a back-up satellite-based comms link. If there is failure on the wireless mesh network, Layer 3 dynamic routing would sense that failure, and redirect all of the data over the sat com link without any user intervention. Had the network been using static routing, a network administrator would have had to manually go in and tell a layer 3 switch or static router what the alternate link was and what IP address to connect to on the satellite network.

When architecting your Ethernet network; size, criticality of data, the number of nodes on the network, the need for privacy over VLANs and many other features will affect how heavily you invest in in data traffic management—from routers to switches to network administrators. Take a look at all factors before making your final choices.


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