fix: ipv6 gateway mac

src/interface/interface.rs

@@ -105,8 +105,9 @@ pub struct Interface {
     /// Default gateway associated with this interface, when known.
     ///
     /// This field is available only with the `gateway` feature. It may be `None` when the
-    /// interface is not the default route, when the gateway has no link-layer address available,
-    /// or when the platform cannot resolve gateway information.
+    /// interface has no gateway addresses or when the platform cannot obtain gateway
+    /// information. If the gateway addresses are known but the link-layer address cannot be
+    /// resolved, the device contains a zero MAC address.
     #[cfg(feature = "gateway")]
     pub gateway: Option<NetworkDevice>,
     /// DNS resolver addresses associated with this interface.

src/os/android/netlink.rs

@@ -376,24 +376,31 @@ pub fn collect_routes() -> io::Result<HashMap<u32, GwRow>> {
         }
     }
 
+    let mut mac_candidates = crate::os::linux::gateway::GatewayMacCandidates::default();
     for n in neighs {
         let (ip, mac, ifi) = neigh_extract(&n);
         let ifi = match ifi {
             Some(i) => i,
             None => continue,
         };
-        if let Some(row) = m.get_mut(&ifi) {
-            if let (Some(m6), Some(ip)) = (mac, ip) {
-                let hit = match ip {
-                    IpAddr::V4(v4) => row.gw_v4.contains(&v4),
-                    IpAddr::V6(v6) => row.gw_v6.contains(&v6),
-                };
-                if hit {
-                    row.mac = Some(m6);
-                }
+        let (Some(row), Some(m6), Some(ip)) = (m.get_mut(&ifi), mac, ip) else {
+            continue;
+        };
+        match ip {
+            IpAddr::V4(v4) if row.gw_v4.contains(&v4) => {
+                mac_candidates.record_ipv4(ifi, m6);
+            }
+            IpAddr::V6(v6) if row.gw_v6.contains(&v6) => {
+                mac_candidates.record_ipv6(ifi, m6);
             }
+            _ => {}
         }
     }
 
+    for (ifindex, row) in &mut m {
+        // Preserve the established IPv4 result when both families use different routers.
+        row.mac = mac_candidates.get(*ifindex);
+    }
+
     Ok(m)
 }