Strict RPF (NixOS default) drops the encrypted return traffic of an active
exit node: table 52's 'default dev tailscale0' makes the reverse-path lookup
for packets arriving on the physical interface resolve to tailscale0, so they
are dropped before Tailscale decrypts them (rx stays 0). Loose RPF still blocks
spoofed/unroutable sources but removes the interface-match requirement, as
recommended by Tailscale/NixOS for exit nodes and subnet routers.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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