Router Identification Designation in OSPF

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The router ID is used to identify the router in an Autonomous System and is advertised in the OSPF Hello packets sent between routers. Some OSPF configuration information is determined by the highest router ID. In the case of a tie when determining the designated router in an AS, the highest router ID takes precedence.

Although the router need not have any relationship to IP addresses on the router, it is generally accepted practice to make the router ID either the highest or lowest IP address on the router. If the router ID is changed the OSPF protocol should be reinitialized.