# FRRouting Loopback Interfaces and OSPF Costs

DevFeed: [FRRouting Loopback Interfaces and OSPF Costs](<https://devfeed.tech/articles/frrouting-loopback-interfaces-and-ospf-costs-10979.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2024/04/frr-loopback-ospf-cost/>)

Published: 2024-04-17T07:56:00Z

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>), [SR-MPLS](<https://devfeed.tech/topics/sr-mpls.md>), [Linux](<https://devfeed.tech/topics/linux.md>), [Development](<https://devfeed.tech/topics/development.md>)

Tags: [integration](<https://devfeed.tech/tags/integration.md>), [interfaces](<https://devfeed.tech/tags/interfaces.md>), [linux](<https://devfeed.tech/tags/linux.md>), [mpls](<https://devfeed.tech/tags/mpls.md>), [netlab](<https://devfeed.tech/tags/netlab.md>), [networks](<https://devfeed.tech/tags/networks.md>), [ospf](<https://devfeed.tech/tags/ospf.md>), [sr-mpls](<https://devfeed.tech/tags/sr-mpls.md>), [tests](<https://devfeed.tech/tags/tests.md>)

## AI overview

The article explains that FRRouting advertises the IP prefix on the Linux lo loopback interface with an OSPF cost of zero. It traces the finding to a loopback-interface naming change made while adding FRRouting container support to netlab, and notes that RFC 2328 permits zero OSPF cost on stub networks.

## Source excerpt

TL&DR: FRRouting advertises the IP prefix on the lo loopback interface with zero cost. Let's start with the background story. When we added FRRouting containers support to netlab, someone decided to use lo0 as the loopback interface name. That device doesn't exist in a typical Linux container, but it's not hard to add it: $ ip link add lo0 type dummy $ ip link set dev lo0 up Read more ...