vnet only ever sent IPv6 RAs in response to a Router Solicitation. In
practice this meant gokrazy VMs running with a dual-stack LAN never
installed vnet's IPv6 default route: gokrazy brings the link up via
DHCPv4 and the kernel never emits an RS on its own under that init
path. Off-link IPv6 destinations like the fake DERP servers were
therefore unreachable from any gokrazy test node that also had v4
on the same interface. (Pure-v6 nodes happened to work because the
kernel sends an RS as part of v6-only autoconf.)
Fix this in two complementary ways:
- Send an unsolicited RA every 5s to the link-local all-nodes group
on every v6-enabled network. This matches what real routers do
(RFC 4861 §6.2.1, MaxRtrAdvInterval; we use a much shorter
interval than the spec's 200s default so short-lived tests don't
have to wait).
- Send a unicast RA to a newly-registered MAC as soon as a client
first transmits on the wire. Without this the first periodic RA
can land before any VM has connected and the next one isn't
until the next tick, which can be longer than the test runs.
Factor the RA serialization out into buildIPv6RouterAdvertisement so
the solicited, periodic, and per-client paths all share one body.
Update TestSelfSignedDERPHashPinning to use a dual-stack hard-NAT
builder and assert zero errors from DebugDERPRegion (instead of
filtering "over IPv6" errors as it had to before this change). The
new builder also sets TS_DEBUG_STRIP_ENDPOINTS=1 on tailscaled so
disco can't find a direct path: without endpoint stripping, the now-
working non-NATted IPv6 LAN gives the two hard-NAT'd nodes a direct
route, defeating the test's "must traverse DERP" assertion. (Hard
NAT alone was enough before this change because v6 routing was
broken.) Also update sendBetweenClients in the vnet unit tests to
tolerate the new on-register RA noise on its read path.
Updates #13038
Updates #19973
Change-Id: Ic281dc53702a25fa773c46313f453837814233e8
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad FitzpatrickandBrad Fitzpatrick
9107354488