The overlay address was derived from a WireGuard key, which makes it the
protocol's address — and the whole point of the interface belonging to
the system level is that every protocol carries traffic for the *same*
addresses. A derived-per-protocol address cannot be that.
So the overlay is IPv4 only: allocated at the system level, signed by the
member that holds it, and the same address whichever protocol happens to
be moving the packets. The derivation, its ULA prefix and its constants
are gone, along with the collision rule that existed only because a
derived IPv4 address has too little room to be unique — an allocated one
is unique by construction.
A real loss came with it and is restored explicitly. The announcement was
bound to its network only as a side effect of checking the derived
address, so removing that check removed the binding. It now carries the
network id and rejects a mismatch. Strictly redundant, because a
capability arrives on a session that already proved membership, and kept
because losing a property silently is the wrong way to lose one.
An unlock falls out: the MTU floor of 1280 existed because Linux tears
IPv6 down below it. Without IPv6 the floor is 576, what every IPv4 host
must be able to reassemble, so a relayed path with small datagrams can be
matched rather than warned about. The default stays 1280.
The test that forged an overlay address now forges a network id, which is
what is left to lie about. One flaky assertion fixed while passing: it
waited for "the interface has some address", which is briefly true of the
leftover it was meant to see replaced.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
tsunagiandClaude Opus 5
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