diff --git a/README.md b/README.md
index c6926bb..7fbc8ca 100644
--- a/README.md
+++ b/README.md
@@ -116,10 +116,10 @@ cargo run -p lanparty-gateway -- \
 
 The gateway connects to the relay as `role = gateway`, completes the
 control-stream hello/welcome handshake, opens an AF_PACKET socket on the LAN
-interface, and bridges Ethernet frames between the relay and wired LAN until
-shutdown. It tracks remote-client source MACs seen from relay traffic and
-periodically emits small CAM refresh frames so the physical switch keeps those
-MACs associated with the gateway port.
+interface with promiscuous packet membership, and bridges Ethernet frames
+between the relay and wired LAN until shutdown. It tracks remote-client source
+MACs seen from relay traffic and periodically emits small CAM refresh frames so
+the physical switch keeps those MACs associated with the gateway port.
 
 ## Windows Client
 
diff --git a/crates/lanparty-gateway/src/packet.rs b/crates/lanparty-gateway/src/packet.rs
index 8136655..f090341 100644
--- a/crates/lanparty-gateway/src/packet.rs
+++ b/crates/lanparty-gateway/src/packet.rs
@@ -58,6 +58,7 @@ impl PacketSocket {
         if result < 0 {
             return Err(io::Error::last_os_error());
         }
+        enable_promiscuous_membership(fd.as_raw_fd(), interface_index)?;
         let interface_mac = interface_hardware_addr(fd.as_raw_fd(), interface)?;
 
         Ok(Self {
@@ -153,6 +154,37 @@ pub fn interface_index(interface: &str) -> io::Result<u32> {
     Ok(index)
 }
 
+fn enable_promiscuous_membership(fd: RawFd, interface_index: u32) -> io::Result<()> {
+    let membership = promiscuous_membership(interface_index);
+    let result = unsafe {
+        // SAFETY: membership points to a fully initialized packet_mreq and the provided length
+        // matches that kernel ABI struct. The socket fd is owned by PacketSocket::open.
+        libc::setsockopt(
+            fd,
+            libc::SOL_PACKET,
+            libc::PACKET_ADD_MEMBERSHIP,
+            (&membership as *const libc::packet_mreq).cast::<libc::c_void>(),
+            std::mem::size_of::<libc::packet_mreq>() as libc::socklen_t,
+        )
+    };
+    if result < 0 {
+        return Err(io::Error::last_os_error());
+    }
+
+    Ok(())
+}
+
+fn promiscuous_membership(interface_index: u32) -> libc::packet_mreq {
+    let mut membership = unsafe {
+        // SAFETY: packet_mreq is a plain kernel ABI struct; zeroing leaves unused fields empty.
+        std::mem::zeroed::<libc::packet_mreq>()
+    };
+    membership.mr_ifindex = interface_index as libc::c_int;
+    membership.mr_type = libc::PACKET_MR_PROMISC as libc::c_ushort;
+
+    membership
+}
+
 fn interface_name(interface: &str) -> io::Result<CString> {
     if interface.trim().is_empty() {
         return Err(io::Error::new(
@@ -258,6 +290,16 @@ mod tests {
         assert_ne!(error.kind(), io::ErrorKind::InvalidInput);
     }
 
+    #[test]
+    fn builds_promiscuous_packet_membership_request() {
+        let membership = promiscuous_membership(12);
+
+        assert_eq!(membership.mr_ifindex, 12);
+        assert_eq!(membership.mr_type, libc::PACKET_MR_PROMISC as u16);
+        assert_eq!(membership.mr_alen, 0);
+        assert_eq!(membership.mr_address, [0; 8]);
+    }
+
     #[test]
     fn classifies_inbound_packet_types() {
         assert!(!is_inbound_packet_type(libc::PACKET_OUTGOING));