Step 1. Static Routing¶
Introduction¶
Welcome to the RIP (Routing Information Protocol) tutorial for the INET Framework. This tutorial series will guide you through understanding and experimenting with the RIP routing protocol implementation in OMNeT++. RIP is one of the oldest distance-vector routing protocols, and despite its limitations, it remains useful for understanding fundamental routing concepts.
Before diving into the dynamic routing capabilities of RIP, we’ll start with static routing to establish a baseline understanding of our network topology and routing concepts. This approach allows us to compare static and dynamic routing behaviors in later steps.
Goals¶
In this first step, our goals are to:
Familiarize ourselves with the experimental network topology that we’ll use throughout the tutorial
Understand how static routing works using the Ipv4NetworkConfigurator module
Observe how packets travel through a network with pre-configured routing tables
Establish a baseline for comparison with dynamic RIP routing in subsequent steps
The Network Model¶
Our network consists of three switched LANs connected by routers to form an internetwork. Each LAN contains multiple hosts connected to an Ethernet switch. The LANs are interconnected through a network of routers, creating multiple possible paths between endpoints.
Key components of the network:
Three LANs: Each with a switch and multiple hosts
Five routers: Connecting the LANs and providing multiple routing paths
Connection types: A mix of 10Mbps and 100Mbps Ethernet links
Host0 and Host6: Special hosts (highlighted in red and blue) that we’ll use for testing connectivity
The complete network topology is defined in the RipNetworkA.ned file. The
network is designed to demonstrate various routing scenarios in the following
steps, including route discovery, convergence, and handling of link failures.
Static Routing Configuration¶
In this step, we use static routing rather than RIP. Static routing means that the routing tables are calculated and configured at the beginning of the simulation and remain unchanged throughout. This is handled by the Ipv4NetworkConfigurator module, which performs two essential tasks:
Address Assignment: Automatically assigns IP and MAC addresses to all network interfaces, saving us from the tedious process of manual configuration
Route Calculation: Computes optimal routes between all network nodes and populates the routing tables accordingly
The configurator uses graph algorithms to determine the shortest paths between nodes, ensuring efficient routing. It’s important to note that in this step, once the routing tables are set up, they remain static - there’s no dynamic adaptation to network changes as would happen with RIP.
The configuration in omnetpp.ini for Step 1 includes:
[Config Step1]
description = "Static routing"
network = RipNetworkA
sim-time-limit = 100s
# do not add direct routes
*.configurator.addDirectRoutes = false
# Application parameters
*.host0.numApps = 1
*.host0.app[0].typename = "PingApp"
*.host0.app[0].destAddr = "host6"
*.*.ipv4.arp.typename = "GlobalArp"
# Visualizer settings
*.visualizer.interfaceTableVisualizer[0].displayInterfaceTables = true
Note the addDirectRoutes = false setting, which instructs the configurator
not to add routes to directly connected networks automatically. This makes the
routing configuration more explicit and easier to understand for our learning
purposes.
Experiment: Testing Connectivity¶
To test the routing configuration, we set up a simple experiment where host0
sends ping packets to host6. This allows us to observe how packets traverse
the network using the pre-configured static routes.
When the simulation starts:
The configurator module assigns addresses to all interfaces
The configurator calculates optimal routes and populates routing tables
host0begins sending ICMP echo (ping) requests tohost6The packets travel through the network following the routes in the routing tables
host6responds with ICMP echo replies that travel back tohost0
The visualization settings in the general section of omnetpp.ini help us observe the routing paths:
*.visualizer.routingTableVisualizer[0].destinationFilter = "host0"
*.visualizer.routingTableVisualizer[0].lineColor = "red"
*.visualizer.routingTableVisualizer[1].destinationFilter = "host6"
*.visualizer.routingTableVisualizer[1].lineColor = "blue"
These settings display:
Red arrows: Routes towards
host0Blue arrows: Routes towards
host6
The following video demonstrates the simulation:
Observing the Routing Paths¶
In the simulation, you can observe:
Complete routing paths: The network has full connectivity with pre-configured optimal routes
Bidirectional communication: Packets can flow in both directions between
host0andhost6Multiple routing paths: The network has redundant paths, though only the optimal ones are used with static routing
This screenshot shows the routing paths (red towards host0, blue towards host6):
Notice how the routing tables are complete from the start of the simulation. This is the key difference from dynamic routing protocols like RIP, where routes are discovered gradually through router advertisements.
Conclusion and Next Steps¶
In this step, we’ve established our network topology and observed how static routing works with pre-configured routing tables. The Ipv4NetworkConfigurator has done all the hard work of calculating optimal routes and setting up the routing tables.
While static routing works well in this stable network, it has limitations:
It doesn’t adapt to network changes (link failures, new routers, etc.)
It requires manual reconfiguration when the network topology changes
It doesn’t scale well to large, dynamic networks
In the next step, we’ll introduce RIP and observe how routers dynamically build their routing tables through the exchange of routing information. This will demonstrate how RIP discovers routes and converges to a stable routing state without pre-configuration.
Sources:
omnetpp.ini,
RipNetworkA.ned
Discussion¶
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