try to force the detection of multicast interface

proxy/src/forwarder.rs

@@ -40,6 +40,8 @@ use crate::{
     resolve_hostname_port, ShredstreamProxyError,
 };
 
+use crate::multicast_config::{ipv4_addr_for_device, ifindex_for_device};
+
 // values copied from https://github.com/solana-labs/solana/blob/33bde55bbdde13003acf45bb6afe6db4ab599ae4/core/src/sigverify_shreds.rs#L20
 pub const DEDUPER_FALSE_POSITIVE_RATE: f64 = 0.001;
 pub const DEDUPER_NUM_BITS: u64 = 637_534_199; // 76MB
@@ -54,6 +56,7 @@ pub fn start_forwarder_threads(
     src_port: u16,
     maybe_multicast_socket: Option<Vec<UdpSocket>>,
     maybe_triton_multicast_socket: Option<(IpAddr, Vec<UdpSocket>)>,
+    maybe_multicast_ifname: Option<String>,
     num_threads: Option<usize>,
     deduper: Arc<RwLock<Deduper<2, [u8]>>>,
     should_reconstruct_shreds: bool,
@@ -240,7 +243,8 @@ pub fn start_forwarder_threads(
     if let Some((multicast_origin, multicast_socket)) = maybe_triton_multicast_socket {
         start_multicast_forwarder_thread(
             multicast_origin, 
-            multicast_socket, 
+            multicast_socket,
+            maybe_multicast_ifname,
             recycler, 
             reconstruct_tx, 
             unioned_dest_sockets, 
@@ -277,6 +281,7 @@ pub struct MulticastSource {
 pub fn start_multicast_forwarder_thread(
     multicast_origin: IpAddr,
     sockets: Vec<UdpSocket>,
+    maybe_multicast_ifname: Option<String>,
     recycler: PacketBatchRecycler,
     reconstruct_tx: crossbeam_channel::Sender<PacketBatch>,
     unioned_dest_sockets: Arc<ArcSwap<Vec<SocketAddr>>>,
@@ -313,7 +318,7 @@ pub fn start_multicast_forwarder_thread(
         let reconstruct_tx = reconstruct_tx.clone();
         let exit = exit.clone();
 
-
+        let ifname_opt = maybe_multicast_ifname.clone();
 
         let send_thread = Builder::new()
             .name(format!("ssPxyTxMulticast_{thread_id}"))
@@ -326,6 +331,11 @@ pub fn start_multicast_forwarder_thread(
                     match try_create_ipv6_socket(ipv6_addr) {
                         Ok(socket) => {
                             info!("Successfully bound send socket to IPv6 dual-stack address.");
+                            if let Some(ifname) = &ifname_opt {
+                                if let Ok(Some(idx)) = ifindex_for_device(ifname) {
+                                    let _ = socket.set_multicast_if_v6(idx);
+                                }
+                            }
                             socket.set_multicast_loop_v6(false)
                               .expect("Failed to disable IPv6 multicast loopback");
                             socket
@@ -337,6 +347,19 @@ pub fn start_multicast_forwarder_thread(
                             let socket = UdpSocket::bind(ipv4_addr)
                                 .expect("Failed to bind to IPv4 socket after IPv6 failed");
                             socket.set_multicast_ttl_v4(IP_MULTICAST_TTL).expect("IP_MULTICAST_TTL_V4");
+
+                            if let Some(ifname) = &ifname_opt {
+                                match ipv4_addr_for_device(ifname) {
+                                    Ok(Some(device_ip)) => {
+                                        info!("Binding multicast output for {} to interface IP: {}", ifname, device_ip);
+                                        socket.set_multicast_if_v4(&device_ip)
+                                            .expect("Failed to set multicast output interface");
+                                    }
+                                    Ok(None) => warn!("Interface {} has no IPv4 address; skipping set_multicast_if_v4", ifname),
+                                    Err(e) => warn!("Failed to resolve interface {}: {}", ifname, e),
+                                }
+                            }
+
                             socket.set_multicast_loop_v4(false)
                                 .expect("Failed to disable IPv4 multicast loopback");
                             socket

proxy/src/main.rs

@@ -348,6 +348,7 @@ fn main() -> Result<(), ShredstreamProxyError> {
         args.src_bind_port,
         maybe_multicast_socket,
         maybe_triton_multicast_socket,
+        maybe_multicast_ifname,
         args.num_threads,
         deduper.clone(),
         args.grpc_service_port.is_some(),