[holowoodman]

IMHO all this whining about "layering violations" is stupid. One will always need some kind of layer glue, neighbors bordering on each other need to know something about each other, correlate addresses, etc. It is impossible to do anything practical without such violations. And it doesn't really matter if that glue protocol belongs to the below layer, the above layer or is a weird hybrid of both. Because in the end, the glue will necessarily be a hybrid and it will be specific to the combination of both those layers.

The only thing one should really really really avoid is the TCP mistake of not just having some minimally necessary glue, but that tight coupling of TCP connections to IP addresses in the layer below.

[pocksuppet]

It's a layering violation because it makes the inter-layer-glue more messy than it should be. IPv6 having a circular layer dependency on itself is not a good thing. It makes that glue messy. ARP is cleaner glue.