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e5382133c5
Add a selftest to verify that FOU-encapsulated packets addressed to a multicast destination are correctly resubmitted to the inner protocol handler (GRE) via the UDP multicast delivery path. Both IPv4 and IPv6 paths are tested. The test creates two network namespaces connected by a veth pair with a FOU/GRETAP (IPv4) and FOU/ip6gretap (IPv6) tunnel using multicast remote addresses (239.0.0.1 and ff0e::1). Ping is sent through each tunnel and received packets are counted on the receiver's tunnel interface. The veth pair is created directly inside the namespaces to avoid possible name collisions with devices in the root namespace. Static neighbor entries are configured on the sender because ARP/ND replies from the receiver cannot traverse the unidirectional multicast tunnel back to the sender. The early demux optimization (net.ipv4.ip_early_demux, which controls both IPv4 and IPv6) is disabled on the receiver to force packets through __udp4_lib_mcast_deliver() / __udp6_lib_mcast_deliver(), which is the code path being tested. Signed-off-by: Anton Danilov <littlesmilingcloud@gmail.com> Assisted-by: Claude:claude-opus-4-6 Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/a5b65f092d22a12b52fc536c0565b948cd8ecae3.1783372173.git.littlesmilingcloud@gmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>