Re: Debian jessie > buster IPv6 link scope change of behaviour
On Thu, Jan 21, 2021 at 08:04:05AM +0100, Marc SCHAEFER wrote:
> fe80::1 is specifically a link-local scope, a bit like if you try to
> access a class variable without telling in what class it is.
Reading RFC-4291 [1], 2.5.6 (link-local addresses) and RFC-4007 [2] 6,
Zones Indices:
Because the same non-global address may be in use in more than one
zone of the same scope (e.g., the use of link-local address fe80::1
in two separate physical links) and a node may have interfaces
attached to different zones of the same scope (e.g., a router
normally has multiple interfaces attached to different links), a node
*requires* an internal means to identify to which zone a non-global
address belongs. This is accomplished by assigning, within the node,
a distinct "zone index" to each zone of the same scope to which that
node is attached, and by allowing all internal uses of an address to
be qualified by a zone index.
Also:
An implementation should also support the concept of a "default" zone
for each scope. And, when supported, the index value zero at each
scope SHOULD be reserved to mean "use the default zone". Unlike
other zone indices, the default index does not contain any scope, and
the scope is determined by the address that the default index
accompanies. An implementation may additionally define a separate
default zone for each scope. Those default indices can also be used
as the zone qualifier for an address for which the node is attached
to only one zone; e.g., when using global addresses.
If I read well, recent Linux kernels might have decided that the first
Ethernet interface is the default zone. Or at least this is how I
understand the *requires* above.
[1] https://tools.ietf.org/html/rfc4291#section-2.5.6
[2] https://tools.ietf.org/html/rfc4007
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