Lan? [LWN.net]

Lan?

Posted Jul 22, 2026 13:19 UTC (Wed) by TomH (subscriber, #56149)
In reply to: Lan? by dskoll
Parent article: Firefox 153 released

That might make sense, but it's not how https://wicg.github.io/local-network-access/#ip-address-s... says the decision should be made.

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Lan?

Posted Jul 22, 2026 13:29 UTC (Wed) by dskoll (subscriber, #1630) [Link] (2 responses)

I think the Mozilla developers have made a fundamental misunderstanding. The document you link to that defines "local" addresses refers, I believe, to those addresses that may be managed locally without requiring coordination with the wider Internet.

But for security purposes, again IMO, "local" addresses should refer to those addresses that are directly on the LAN... in other words, everything that is 1 hop away at most. For more security, it should probably also refer to locally-managed addresses described in your link because a lot of companies do route those addresses internally and they may be more than 1 hop away. So a union of the two.

Lan?

Posted Jul 22, 2026 17:40 UTC (Wed) by Cyberax (✭ supporter ✭, #52523) [Link]

Welcome to IPv6, the world of recursive WTFs!

There is no concept of "local" networks in IPv6, there is a notion of "on-link" networks. Which does not _necessarily_ correspond to the networks that are directly accessible in the same Ethernet collision domain.

That's because IPv6 uses multicasts instead of broadcasts for neighbor discovery, so you can have a multicast router bridging multiple Ethernet segments together. Just like proxy ARP in IPv4, but in IPv6 it's actually exposed to the host.

For an additional fun, on-link relations do not necessarily have to be transitive and they can have overlapping prefix lengths.

See: https://datatracker.ietf.org/doc/html/rfc5942 and https://datatracker.ietf.org/doc/html/rfc4943

Lan?

Posted Jul 23, 2026 9:23 UTC (Thu) by taladar (subscriber, #68407) [Link]

While most (non-server) devices are not directly connected to the internet you can not necessarily assume that just because a device has a subnet on a local interface that that subnet isn't a public network.