Rules based on which OSPF selects router IDs of S series switches

A router ID is used to uniquely identify a device on an OSPF network. Therefore, each router ID in an OSPF process must be unique. Otherwise, an OSPF neighbor relationship cannot be established and routing information is incorrect. You are advised to configure a unique router ID for each OSPF process on an OSPF device.
You can configure the router ID manually. If no router ID is specified through a command, the system selects an IP address of an interface as the router ID. The largest loopback interface IP address is used as the router ID. If no loopback interface is configured, the largest physical interface IP address is used as the router ID.

The router ID is reselected in the following scenarios:
The ospf xx router-id x.x.x.x command is used to reconfigure a router ID of an OSPF device.
The router ID of a system is reconfigured and the OSPF process is restarted.
The IP address that was selected as the router ID of a system is deleted and the OSPF process is restarted.

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