The “Passive” option in OSPF interfaces on MikroTik devices is used to control the behavior of advertisements and adjacency relationships in OSPF (Open Shortest Path First) networks. Marking an interface as passive tells OSPF not to send or receive OSPF “hello” packets over that interface.

This has several implications and uses in the configuration and operation of OSPF networks:

1. Security and Access Control

• By marking an interface as passive, you prevent other OSPF routers from forming an adjacency through that interface. This is useful on interfaces that are connected to networks where there are no other OSPF devices or on interfaces that do not require participation in the OSPF routing process, such as those connected to local area networks (LANs) with end devices.
• It helps prevent unnecessary exposure of routing information and reduces the risk of attacks or unauthorized configurations on the network.

2. Resource Optimization

• Limits resource usage on the router, as OSPF will not attempt to establish adjacencies or send OSPF “hello” packets over passive interfaces. This is especially useful in large networks with many interfaces, where only a few participate in OSPF routing.
• Reduces OSPF traffic on the network as advertisements are not sent over interfaces that do not require participation in OSPF, thereby improving network efficiency.

3. Network Configuration Simplification

• It facilitates clearer and simpler network configuration by allowing you to explicitly specify which interfaces should participate in OSPF routing and which should not.
• It allows network administrators to have finer control over the routing topology, ensuring that OSPF routing only occurs where it is strictly necessary.

Implementation in MikroTik

In MikroTik RouterOS, configuring an OSPF interface as passive can be easily done via the command line interface (CLI) or using WinBox, the graphical user interface (GUI). The command in the CLI to make a passive interface would be something like:

/routing ospf interface add interface=ether1 passive=yes

Or, if an interface configuration already exists, you can modify it to set the “passive” property to “yes.”

Conclusion

The “Passive” option in OSPF interfaces in MikroTik is a powerful tool for network administrators, offering benefits in security, resource optimization and simplification of network configuration.

Its proper use contributes to a more secure and efficient network, allowing OSPF to run only where it is needed and desired.