On use of link-local addresses by IPv6 applications

I see several general problems with the use of link-local addresses by apps:

  1. By design, they won't route outside a single link, but even for small ad hoc networks or home networks we're seeing a mixture of link technologies in use. Yes, you can sometimes bridge them, but not always, and bridging introduces its own set of problems.
  2. Not all apps can use them, and many of those that can use LLs cannot use them in all conditions, depending on (to users) obscure details of the way the network is organized. It would be better if small networks behaved in ways that ordinary users could understand and predict.
  3. Of the apps that can use them, sometimes you have to configure the app to behave differently depending on the network configuration. For instance, under normal circumstances you might want the app to ignore LL addresses, but if it's running on an isolated single-link network then you might have to configure the app to use them. And in general you can't expect the app to detect this.
  4. A network that is initially single-link might acquire some external connections and routing capability, and transitioning apps from LL to another kind of address (so that other nodes can participate in existing apps) is disruptive.
That, and we need a solution for self-organizing networks anyway, and there seem to be good reasons to treat a single-link network as just a component of (or a trivial case of) a self-organizing network.

Granted, we don't have the technology for self-organizing networks yet. In the meantime, people will have to cope with whatever is already there. But think our efforts are better directed toward making self-organizing networks function well than to try to make LLs be the solution for such networks.

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