Step 5. Effect of network type of an interface on routing table routes¶
Goals¶
The goal of this step is to demonstrate how the OSPF network type of an interface affects the routing table entries.
OSPF supports different network types: Point-to-Point, Broadcast, NBMA (Non-Broadcast Multi-Access), Point-to-Multipoint, and others. The network type determines how OSPF behaves on that interface, including whether a Designated Router (DR) is elected and how the network is represented in LSAs and routing tables.
Broadcast networks (e.g., Ethernet): Use DR/BDR election, described by Network LSAs.
Point-to-Point networks (e.g., PPP links): No DR election, direct adjacencies.
The network type affects both the OSPF protocol operation and how routes appear in the routing table.
Configuration¶
This step uses the InterfaceNetworkType network to demonstrate different network types.
The configuration in omnetpp.ini is the following:
[Config Step5]
description = "Effect of network type of an interface on routing table routes"
network = InterfaceNetworkType
*.configurator.configureIsolatedNetworksSeparatly = true
*.configurator.config = xml("<config> \
<interface hosts='**' address='10.x.x.x' netmask='255.x.x.x'/> \
<route hosts='host*' destination='*' netmask='0.0.0.0' interface='eth0' /> \
</config>")
**.visualizer.interfaceTableVisualizer.displayInterfaceTables = true
**.visualizer.interfaceTableVisualizer.nodeFilter = "not *.N*"
# application parameters
*.host8.numApps = 1
*.host8.app[0].typename = "PingApp"
*.host8.app[0].destAddr = "host11"
*.host8.app[0].startTime = 60s
Results¶
The simulation shows how different OSPF network types result in different routing table entries and OSPF behavior:
Broadcast interfaces: OSPF elects a DR and BDR. The network is represented by a Network LSA originated by the DR. Routes to the network show the DR’s interface as the next hop.
Point-to-Point interfaces: No DR election occurs. The link is represented directly in Router LSAs from both ends. Routes show direct next-hop addresses.
The OSPF module logs and routing tables demonstrate how network type configuration affects:
Neighbor discovery and adjacency formation
LSA generation and flooding
Routing table entries and next-hop selection
Understanding network types is crucial for correctly configuring OSPF on different media types and troubleshooting adjacency issues.
Sources:
omnetpp.ini,
InterfaceNetworkType.ned
Discussion¶
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