# Response: True Unnumbered Interfaces

DevFeed: [Response: True Unnumbered Interfaces](<https://devfeed.tech/articles/response-true-unnumbered-interfaces-11191.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2025/05/true-unnumbered-interfaces/>)

Published: 2025-05-22T05:55:00Z

Content type: article

Language: en

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

Topics: [IS-IS](<https://devfeed.tech/topics/is-is.md>), [networking](<https://devfeed.tech/topics/networking.md>), [Linux](<https://devfeed.tech/topics/linux.md>), [Routing (disambiguation)](<https://devfeed.tech/topics/routing.md>)

Tags: [configuration](<https://devfeed.tech/tags/configuration.md>), [interface](<https://devfeed.tech/tags/interface.md>), [ip-routing](<https://devfeed.tech/tags/ip-routing.md>), [ipv4](<https://devfeed.tech/tags/ipv4.md>), [ipv6](<https://devfeed.tech/tags/ipv6.md>), [is-is](<https://devfeed.tech/tags/is-is.md>), [linux](<https://devfeed.tech/tags/linux.md>), [networking-fundamentals](<https://devfeed.tech/tags/networking-fundamentals.md>), [ospf](<https://devfeed.tech/tags/ospf.md>), [protocol](<https://devfeed.tech/tags/protocol.md>), [router](<https://devfeed.tech/tags/router.md>), [routing](<https://devfeed.tech/tags/routing.md>)

## AI overview

This article explains why routers commonly associate IP addresses with interfaces and examines how IS-IS handles unnumbered interfaces. It contrasts IS-IS with OSPF and describes IPv4 next-hop requirements, IPv6 link-local operation, and implementation-specific approaches such as those used by EBGP.

## Source excerpt

Hendrik left an interesting comment on my Running IS-IS over Unnumbered Ethernet Interfaces blog post: FRRouting (Linux) with pure IS-IS, the only way it currently (10.3) works is to copy the loopback IPv4 address to the interfaces that you need to do IPv4 routing on. The OpenFabric (IS-IS "extension" draft) does support true unnumbered interfaces and routes IPv6. Let's unpack this. There are (at least) four reasons a router needs an address associated with an interface1: Read more ...