# OSPF Router ID and Loopback Interface Myths

DevFeed: [OSPF Router ID and Loopback Interface Myths](<https://devfeed.tech/articles/ospf-router-id-and-loopback-interface-myths-11267.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2025/10/ospf-routerid-loopback-interface-myths/>)

Published: 2025-10-21T06:14:00Z

Content type: article

Language: en

Sources: [ipSpace.net blog](<https://devfeed.tech/sources/ipspace-net-blog.md>)

Topics: [Networks](<https://devfeed.tech/topics/networks.md>), [Cisco](<https://devfeed.tech/topics/cisco.md>)

Tags: [cisco](<https://devfeed.tech/tags/cisco.md>), [configuration](<https://devfeed.tech/tags/configuration.md>), [id](<https://devfeed.tech/tags/id.md>), [interface](<https://devfeed.tech/tags/interface.md>), [ipv4](<https://devfeed.tech/tags/ipv4.md>), [networks](<https://devfeed.tech/tags/networks.md>), [ospf](<https://devfeed.tech/tags/ospf.md>), [router](<https://devfeed.tech/tags/router.md>)

## AI overview

The article explains that an OSPF router ID is a 32-bit identifier rather than inherently an IPv4 address. It recounts Cisco's historical router ID selection behavior, including the later use of loopback addresses for greater stability and the router-id command, and discusses Cisco IOS handling of duplicate router IDs.

## Source excerpt

Daniel Dib wrote a nice article describing the history of the loopback interface1, triggering an inevitable mention of the role of a loopback interface in OSPF and related flood of ancient memories on my end. Before going into the details, let's get one fact straight: an OSPF router ID was always (at least from the days of OSPFv1 described in RFC 1133) just a 32-bit identifier, not an IPv4 address2. Straight from the RFC 1133: Read more ...