diff --git a/crates/wzp-client/src/featherchat.rs b/crates/wzp-client/src/featherchat.rs
index 4fe27c9..428a27b 100644
--- a/crates/wzp-client/src/featherchat.rs
+++ b/crates/wzp-client/src/featherchat.rs
@@ -110,6 +110,9 @@ pub fn signal_to_call_type(signal: &SignalMessage) -> CallSignalType {
         SignalMessage::SessionForward { .. } => CallSignalType::Offer, // reuse
         SignalMessage::SessionForwardAck { .. } => CallSignalType::Offer, // reuse
         SignalMessage::RoomUpdate { .. } => CallSignalType::Offer, // reuse
+        SignalMessage::FederationRoomJoin { .. }
+        | SignalMessage::FederationRoomLeave { .. }
+        | SignalMessage::FederationParticipantUpdate { .. } => CallSignalType::Offer, // relay-only
     }
 }
 
diff --git a/crates/wzp-proto/src/packet.rs b/crates/wzp-proto/src/packet.rs
index 1e3909e..2352f54 100644
--- a/crates/wzp-proto/src/packet.rs
+++ b/crates/wzp-proto/src/packet.rs
@@ -656,6 +656,25 @@ pub enum SignalMessage {
         /// List of participants currently in the room.
         participants: Vec<RoomParticipant>,
     },
+
+    // ── Federation signals (relay-to-relay) ──
+
+    /// Federation: a room exists on the sending relay with active local participants.
+    FederationRoomJoin {
+        room: String,
+        participants: Vec<RoomParticipant>,
+    },
+
+    /// Federation: a room is now empty on the sending relay.
+    FederationRoomLeave {
+        room: String,
+    },
+
+    /// Federation: local participant list changed for a federated room.
+    FederationParticipantUpdate {
+        room: String,
+        participants: Vec<RoomParticipant>,
+    },
 }
 
 /// A participant entry in a RoomUpdate message.
diff --git a/crates/wzp-relay/Cargo.toml b/crates/wzp-relay/Cargo.toml
index 9e85240..6014314 100644
--- a/crates/wzp-relay/Cargo.toml
+++ b/crates/wzp-relay/Cargo.toml
@@ -29,6 +29,7 @@ axum = { version = "0.7", default-features = false, features = ["tokio", "http1"
 tower-http = { version = "0.6", features = ["fs"] }
 futures-util = "0.3"
 dirs = "6"
+sha2 = { workspace = true }
 
 [[bin]]
 name = "wzp-relay"
diff --git a/crates/wzp-relay/src/federation.rs b/crates/wzp-relay/src/federation.rs
new file mode 100644
index 0000000..a51dd31
--- /dev/null
+++ b/crates/wzp-relay/src/federation.rs
@@ -0,0 +1,284 @@
+//! Relay federation — connects to peer relays and bridges rooms with matching names.
+//!
+//! Each federated peer is represented as a virtual participant in shared rooms.
+//! Media from local participants is forwarded to the peer via room-tagged datagrams.
+//! Media from the peer is received, demuxed by room hash, and forwarded to local participants.
+
+use std::collections::HashMap;
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::time::Duration;
+
+use bytes::Bytes;
+use sha2::{Sha256, Digest};
+use tokio::sync::Mutex;
+use tracing::{error, info, warn};
+
+use wzp_proto::{MediaTransport, SignalMessage};
+use wzp_transport::QuinnTransport;
+
+use crate::config::PeerConfig;
+use crate::room::{self, ParticipantSender, RoomManager};
+
+/// Compute 8-byte room hash for federation datagram tagging.
+pub fn room_hash(room_name: &str) -> [u8; 8] {
+    let h = Sha256::digest(room_name.as_bytes());
+    let mut out = [0u8; 8];
+    out.copy_from_slice(&h[..8]);
+    out
+}
+
+/// Manages federation connections to peer relays.
+pub struct FederationManager {
+    peers: Vec<PeerConfig>,
+    room_mgr: Arc<Mutex<RoomManager>>,
+    endpoint: quinn::Endpoint,
+    local_tls_fp: String,
+}
+
+impl FederationManager {
+    pub fn new(
+        peers: Vec<PeerConfig>,
+        room_mgr: Arc<Mutex<RoomManager>>,
+        endpoint: quinn::Endpoint,
+        local_tls_fp: String,
+    ) -> Self {
+        Self {
+            peers,
+            room_mgr,
+            endpoint,
+            local_tls_fp,
+        }
+    }
+
+    /// Start federation — spawns one task per configured peer.
+    pub async fn run(self: Arc<Self>) {
+        if self.peers.is_empty() {
+            return;
+        }
+        info!(peers = self.peers.len(), "federation starting");
+        let mut handles = Vec::new();
+        for peer in &self.peers {
+            let this = self.clone();
+            let peer = peer.clone();
+            handles.push(tokio::spawn(async move {
+                run_peer_loop(this, peer).await;
+            }));
+        }
+        for h in handles {
+            let _ = h.await;
+        }
+    }
+
+    /// Handle an inbound federation connection from a peer that we recognize.
+    pub async fn handle_inbound(
+        self: &Arc<Self>,
+        transport: Arc<QuinnTransport>,
+        peer_config: PeerConfig,
+    ) {
+        let addr: SocketAddr = peer_config.url.parse().unwrap_or_else(|_| "0.0.0.0:0".parse().unwrap());
+        info!(peer = ?peer_config.label, %addr, "inbound federation link active");
+        if let Err(e) = run_federation_link(self.clone(), transport, addr, &peer_config).await {
+            warn!(peer = ?peer_config.label, "inbound federation link ended: {e}");
+        }
+    }
+
+    /// Find a configured peer by TLS fingerprint.
+    pub fn find_peer_by_fingerprint(&self, fp: &str) -> Option<&PeerConfig> {
+        self.peers.iter().find(|p| normalize_fp(&p.fingerprint) == normalize_fp(fp))
+    }
+}
+
+/// Normalize a fingerprint string (remove colons, lowercase).
+fn normalize_fp(fp: &str) -> String {
+    fp.replace(':', "").to_lowercase()
+}
+
+/// Persistent connection loop for one peer — reconnects with backoff.
+async fn run_peer_loop(fm: Arc<FederationManager>, peer: PeerConfig) {
+    let mut backoff = Duration::from_secs(5);
+    loop {
+        info!(peer_url = %peer.url, label = ?peer.label, "federation: connecting to peer...");
+        match connect_to_peer(&fm, &peer).await {
+            Ok(transport) => {
+                backoff = Duration::from_secs(5); // reset on success
+                let addr: SocketAddr = peer.url.parse().unwrap_or_else(|_| "0.0.0.0:0".parse().unwrap());
+                if let Err(e) = run_federation_link(fm.clone(), transport, addr, &peer).await {
+                    warn!(peer_url = %peer.url, "federation link ended: {e}");
+                }
+            }
+            Err(e) => {
+                warn!(peer_url = %peer.url, backoff_s = backoff.as_secs(), "federation connect failed: {e}");
+            }
+        }
+        tokio::time::sleep(backoff).await;
+        backoff = (backoff * 2).min(Duration::from_secs(300));
+    }
+}
+
+/// Connect to a peer relay.
+async fn connect_to_peer(fm: &FederationManager, peer: &PeerConfig) -> Result<Arc<QuinnTransport>, anyhow::Error> {
+    let addr: SocketAddr = peer.url.parse()?;
+    let client_cfg = wzp_transport::client_config();
+    let conn = wzp_transport::connect(&fm.endpoint, addr, "_federation", client_cfg).await?;
+    // TODO: verify peer TLS fingerprint once we have cert access
+    let transport = Arc::new(QuinnTransport::new(conn));
+    info!(peer_url = %peer.url, label = ?peer.label, "federation: connected to peer");
+    Ok(transport)
+}
+
+/// Run the federation link: exchange room info and forward media.
+async fn run_federation_link(
+    fm: Arc<FederationManager>,
+    transport: Arc<QuinnTransport>,
+    peer_addr: SocketAddr,
+    peer: &PeerConfig,
+) -> Result<(), anyhow::Error> {
+    // Announce our active rooms to the peer
+    let rooms = {
+        let mgr = fm.room_mgr.lock().await;
+        mgr.active_rooms()
+    };
+    for room_name in &rooms {
+        let participants = {
+            let mgr = fm.room_mgr.lock().await;
+            mgr.local_participants(room_name)
+        };
+        let msg = SignalMessage::FederationRoomJoin {
+            room: room_name.clone(),
+            participants,
+        };
+        transport.send_signal(&msg).await?;
+    }
+
+    // Track virtual participants we create on behalf of this peer
+    let mut peer_room_participants: HashMap<String, room::ParticipantId> = HashMap::new();
+    // Map room_hash -> room_name for incoming media demux
+    let mut hash_to_room: HashMap<[u8; 8], String> = HashMap::new();
+
+    // Run two tasks: recv signals + recv media datagrams
+    let signal_transport = transport.clone();
+    let media_transport = transport.clone();
+    let fm_signal = fm.clone();
+    let fm_media = fm.clone();
+    let peer_label = peer.label.clone().unwrap_or_else(|| peer.url.clone());
+
+    let signal_task = async move {
+        loop {
+            match signal_transport.recv_signal().await {
+                Ok(Some(msg)) => {
+                    match msg {
+                        SignalMessage::FederationRoomJoin { room, participants } => {
+                            info!(peer = %peer_label, room = %room, count = participants.len(), "federation: peer room join");
+                            let rh = room_hash(&room);
+                            hash_to_room.insert(rh, room.clone());
+
+                            let sender = ParticipantSender::Federation {
+                                transport: signal_transport.clone(),
+                                room_hash: rh,
+                            };
+                            let (pid, update, senders) = {
+                                let mut mgr = fm_signal.room_mgr.lock().await;
+                                mgr.join_federated(&room, peer_addr, sender, participants)
+                            };
+                            peer_room_participants.insert(room, pid);
+                            room::broadcast_signal(&senders, &update).await;
+                        }
+                        SignalMessage::FederationRoomLeave { room } => {
+                            info!(peer = %peer_label, room = %room, "federation: peer room leave");
+                            if let Some(pid) = peer_room_participants.remove(&room) {
+                                let result = {
+                                    let mut mgr = fm_signal.room_mgr.lock().await;
+                                    mgr.leave(&room, pid)
+                                };
+                                if let Some((update, senders)) = result {
+                                    room::broadcast_signal(&senders, &update).await;
+                                }
+                            }
+                            hash_to_room.retain(|_, v| v != &room);
+                        }
+                        SignalMessage::FederationParticipantUpdate { room, participants } => {
+                            let result = {
+                                let mut mgr = fm_signal.room_mgr.lock().await;
+                                mgr.update_federated_participants(&room, peer_addr, participants)
+                            };
+                            if let Some((update, senders)) = result {
+                                room::broadcast_signal(&senders, &update).await;
+                            }
+                        }
+                        _ => {} // ignore other signals
+                    }
+                }
+                Ok(None) => break,
+                Err(e) => {
+                    error!(peer = %peer_label, "federation signal recv error: {e}");
+                    break;
+                }
+            }
+        }
+        // Cleanup: remove all virtual participants for this peer
+        for (room, pid) in &peer_room_participants {
+            let result = {
+                let mut mgr = fm_signal.room_mgr.lock().await;
+                mgr.leave(room, *pid)
+            };
+            if let Some((update, senders)) = result {
+                room::broadcast_signal(&senders, &update).await;
+            }
+        }
+        info!(peer = %peer_label, "federation signal task ended");
+    };
+
+    let media_task = async move {
+        loop {
+            match media_transport.connection().read_datagram().await {
+                Ok(data) => {
+                    if data.len() < 8 + 4 {
+                        continue; // too short (need room_hash + min header)
+                    }
+                    let mut rh = [0u8; 8];
+                    rh.copy_from_slice(&data[..8]);
+                    let media_bytes = &data[8..];
+
+                    // Deserialize media packet
+                    let pkt = match wzp_proto::MediaPacket::from_bytes(Bytes::copy_from_slice(media_bytes)) {
+                        Some(pkt) => pkt,
+                        None => continue,
+                    };
+
+                    // Look up room by hash — we need to get the room name from the signal task's hash_to_room
+                    // For simplicity, we forward to all local participants via the room manager
+                    // The virtual participant approach means we don't need the room name here —
+                    // the SFU loop handles it. But since inbound media doesn't go through run_participant,
+                    // we need to manually fan out.
+
+                    // For now, just use the room manager to find local participants
+                    // This is a simplified approach — full implementation would maintain
+                    // a shared hash_to_room map between signal and media tasks
+                    let mgr = fm_media.room_mgr.lock().await;
+                    for room_name in mgr.active_rooms() {
+                        if room_hash(&room_name) == rh {
+                            // Forward to all local participants in this room
+                            let locals: Vec<_> = mgr.local_senders(&room_name);
+                            drop(mgr); // release lock before sending
+                            for sender in &locals {
+                                if let ParticipantSender::Quic(t) = sender {
+                                    let _ = t.send_media(&pkt).await;
+                                }
+                            }
+                            break;
+                        }
+                    }
+                }
+                Err(_) => break,
+            }
+        }
+    };
+
+    tokio::select! {
+        _ = signal_task => {}
+        _ = media_task => {}
+    }
+
+    Ok(())
+}
diff --git a/crates/wzp-relay/src/lib.rs b/crates/wzp-relay/src/lib.rs
index a798c3a..48e7688 100644
--- a/crates/wzp-relay/src/lib.rs
+++ b/crates/wzp-relay/src/lib.rs
@@ -9,6 +9,7 @@
 
 pub mod auth;
 pub mod config;
+pub mod federation;
 pub mod handshake;
 pub mod metrics;
 pub mod pipeline;
diff --git a/crates/wzp-relay/src/main.rs b/crates/wzp-relay/src/main.rs
index 8f2c6b7..d45ee50 100644
--- a/crates/wzp-relay/src/main.rs
+++ b/crates/wzp-relay/src/main.rs
@@ -320,6 +320,21 @@ async fn main() -> anyhow::Result<()> {
     // Room manager (room mode only)
     let room_mgr = Arc::new(Mutex::new(RoomManager::new()));
 
+    // Federation manager
+    let federation_mgr = if !config.peers.is_empty() {
+        let fm = Arc::new(wzp_relay::federation::FederationManager::new(
+            config.peers.clone(),
+            room_mgr.clone(),
+            endpoint.clone(),
+            tls_fp.clone(),
+        ));
+        let fm_run = fm.clone();
+        tokio::spawn(async move { fm_run.run().await });
+        Some(fm)
+    } else {
+        None
+    };
+
     // Session manager — enforces max concurrent sessions
     let session_mgr = Arc::new(Mutex::new(SessionManager::new(config.max_sessions)));
 
@@ -375,6 +390,7 @@ async fn main() -> anyhow::Result<()> {
         let trunking_enabled = config.trunking_enabled;
         let presence = presence.clone();
         let route_resolver = route_resolver.clone();
+        let federation_mgr = federation_mgr.clone();
 
         tokio::spawn(async move {
             let addr = connection.remote_address();
@@ -482,6 +498,38 @@ async fn main() -> anyhow::Result<()> {
                 return;
             }
 
+            // Federation connections use SNI "_federation"
+            if room_name == "_federation" {
+                if let Some(ref fm) = federation_mgr {
+                    // Check if we recognize this peer by TLS fingerprint
+                    let peer_fp = wzp_transport::tls_fingerprint(
+                        &transport.connection()
+                            .peer_identity()
+                            .and_then(|id| id.downcast::<Vec<rustls::pki_types::CertificateDer>>().ok())
+                            .and_then(|certs| certs.first().cloned())
+                            .map(|c| c.to_vec())
+                            .unwrap_or_default()
+                    );
+                    if let Some(peer_config) = fm.find_peer_by_fingerprint(&peer_fp) {
+                        let peer_config = peer_config.clone();
+                        let fm = fm.clone();
+                        info!(%addr, label = ?peer_config.label, "inbound federation connection accepted");
+                        fm.handle_inbound(transport, peer_config).await;
+                    } else {
+                        warn!(%addr, "unknown relay wants to federate");
+                        info!("  to accept, add to relay.toml:");
+                        info!("  [[peers]]");
+                        info!("  url = \"{addr}\"");
+                        info!("  fingerprint = \"{peer_fp}\"");
+                        transport.close().await.ok();
+                    }
+                } else {
+                    info!(%addr, "federation connection rejected (no peers configured)");
+                    transport.close().await.ok();
+                }
+                return;
+            }
+
             // Auth check: if --auth-url is set, expect first signal message to be a token
             // Auth: if --auth-url is set, expect AuthToken as first signal
             let authenticated_fp: Option<String> = if let Some(ref url) = auth_url {
diff --git a/crates/wzp-relay/src/room.rs b/crates/wzp-relay/src/room.rs
index 70850ad..2bfaab0 100644
--- a/crates/wzp-relay/src/room.rs
+++ b/crates/wzp-relay/src/room.rs
@@ -27,11 +27,25 @@ fn next_id() -> ParticipantId {
     NEXT_PARTICIPANT_ID.fetch_add(1, Ordering::Relaxed)
 }
 
+/// Tracks where a participant originates from (for loop prevention).
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum ParticipantOrigin {
+    /// Connected directly to this relay.
+    Local,
+    /// Virtual participant representing a federated peer relay.
+    Federated { relay_addr: std::net::SocketAddr },
+}
+
 /// How to send data to a participant — either via QUIC transport or WebSocket channel.
 #[derive(Clone)]
 pub enum ParticipantSender {
     Quic(Arc<wzp_transport::QuinnTransport>),
     WebSocket(tokio::sync::mpsc::Sender<Bytes>),
+    /// Federated peer relay — media is prefixed with an 8-byte room hash.
+    Federation {
+        transport: Arc<wzp_transport::QuinnTransport>,
+        room_hash: [u8; 8],
+    },
 }
 
 impl ParticipantSender {
@@ -50,6 +64,14 @@ impl ParticipantSender {
                 };
                 transport.send_media(&pkt).await.map_err(|e| format!("quic send: {e}"))
             }
+            ParticipantSender::Federation { transport, room_hash } => {
+                // Prefix media data with room hash for demuxing on the peer relay
+                let mut tagged = Vec::with_capacity(8 + data.len());
+                tagged.extend_from_slice(room_hash);
+                tagged.extend_from_slice(data);
+                transport.send_raw_datagram(&tagged)
+                    .map_err(|e| format!("federation send: {e}"))
+            }
         }
     }
 
@@ -85,17 +107,21 @@ struct Participant {
     sender: ParticipantSender,
     fingerprint: Option<String>,
     alias: Option<String>,
+    origin: ParticipantOrigin,
 }
 
 /// A room holding multiple participants.
 struct Room {
     participants: Vec<Participant>,
+    /// Remote participants from federated peers (for merged RoomUpdate).
+    federated_participants: HashMap<std::net::SocketAddr, Vec<wzp_proto::packet::RoomParticipant>>,
 }
 
 impl Room {
     fn new() -> Self {
         Self {
             participants: Vec::new(),
+            federated_participants: HashMap::new(),
         }
     }
 
@@ -105,10 +131,11 @@ impl Room {
         sender: ParticipantSender,
         fingerprint: Option<String>,
         alias: Option<String>,
+        origin: ParticipantOrigin,
     ) -> ParticipantId {
         let id = next_id();
-        info!(room_size = self.participants.len() + 1, participant = id, %addr, "joined room");
-        self.participants.push(Participant { id, _addr: addr, sender, fingerprint, alias });
+        info!(room_size = self.participants.len() + 1, participant = id, %addr, ?origin, "joined room");
+        self.participants.push(Participant { id, _addr: addr, sender, fingerprint, alias, origin });
         id
     }
 
@@ -125,15 +152,38 @@ impl Room {
             .collect()
     }
 
-    /// Build a RoomUpdate participant list.
-    fn participant_list(&self) -> Vec<wzp_proto::packet::RoomParticipant> {
+    /// Get senders with loop prevention for federation.
+    ///
+    /// - Media from a **local** participant → send to ALL others (local + federated)
+    /// - Media from a **federated** participant → send to LOCAL participants only
+    ///   (the source relay already forwarded to its own locals and other peers)
+    fn others_for_origin(&self, exclude_id: ParticipantId, source_origin: &ParticipantOrigin) -> Vec<ParticipantSender> {
         self.participants
             .iter()
+            .filter(|p| p.id != exclude_id)
+            .filter(|p| match source_origin {
+                ParticipantOrigin::Local => true,
+                ParticipantOrigin::Federated { .. } => p.origin == ParticipantOrigin::Local,
+            })
+            .map(|p| p.sender.clone())
+            .collect()
+    }
+
+    /// Build a RoomUpdate participant list (local + federated).
+    fn participant_list(&self) -> Vec<wzp_proto::packet::RoomParticipant> {
+        let mut list: Vec<_> = self.participants
+            .iter()
+            .filter(|p| p.origin == ParticipantOrigin::Local)
             .map(|p| wzp_proto::packet::RoomParticipant {
                 fingerprint: p.fingerprint.clone().unwrap_or_default(),
                 alias: p.alias.clone(),
             })
-            .collect()
+            .collect();
+        // Merge federated participants from all peer relays
+        for remote in self.federated_participants.values() {
+            list.extend(remote.iter().cloned());
+        }
+        list
     }
 
     /// Get all senders (for broadcasting to everyone including the joiner).
@@ -214,7 +264,7 @@ impl RoomManager {
             return Err("not authorized for this room".to_string());
         }
         let room = self.rooms.entry(room_name.to_string()).or_insert_with(Room::new);
-        let id = room.add(addr, sender, fingerprint.map(|s| s.to_string()), alias.map(|s| s.to_string()));
+        let id = room.add(addr, sender, fingerprint.map(|s| s.to_string()), alias.map(|s| s.to_string()), ParticipantOrigin::Local);
         let update = wzp_proto::SignalMessage::RoomUpdate {
             count: room.len() as u32,
             participants: room.participant_list(),
@@ -235,6 +285,83 @@ impl RoomManager {
         Ok(id)
     }
 
+    /// Join a room as a federated virtual participant.
+    pub fn join_federated(
+        &mut self,
+        room_name: &str,
+        relay_addr: std::net::SocketAddr,
+        sender: ParticipantSender,
+        remote_participants: Vec<wzp_proto::packet::RoomParticipant>,
+    ) -> (ParticipantId, wzp_proto::SignalMessage, Vec<ParticipantSender>) {
+        let room = self.rooms.entry(room_name.to_string()).or_insert_with(Room::new);
+        room.federated_participants.insert(relay_addr, remote_participants);
+        let id = room.add(
+            relay_addr, sender, None, Some("(federated)".to_string()),
+            ParticipantOrigin::Federated { relay_addr },
+        );
+        let update = wzp_proto::SignalMessage::RoomUpdate {
+            count: room.len() as u32,
+            participants: room.participant_list(),
+        };
+        let senders = room.all_senders();
+        (id, update, senders)
+    }
+
+    /// Update federated participant list for a room (from FederationParticipantUpdate).
+    pub fn update_federated_participants(
+        &mut self,
+        room_name: &str,
+        relay_addr: std::net::SocketAddr,
+        participants: Vec<wzp_proto::packet::RoomParticipant>,
+    ) -> Option<(wzp_proto::SignalMessage, Vec<ParticipantSender>)> {
+        if let Some(room) = self.rooms.get_mut(room_name) {
+            room.federated_participants.insert(relay_addr, participants);
+            let update = wzp_proto::SignalMessage::RoomUpdate {
+                count: room.len() as u32,
+                participants: room.participant_list(),
+            };
+            let senders = room.all_senders();
+            Some((update, senders))
+        } else {
+            None
+        }
+    }
+
+    /// Get the origin of a participant by ID.
+    pub fn participant_origin(&self, room_name: &str, participant_id: ParticipantId) -> Option<ParticipantOrigin> {
+        self.rooms.get(room_name)
+            .and_then(|room| room.participants.iter().find(|p| p.id == participant_id))
+            .map(|p| p.origin.clone())
+    }
+
+    /// Get list of active room names (for federation room announcements).
+    pub fn active_rooms(&self) -> Vec<String> {
+        self.rooms.keys().cloned().collect()
+    }
+
+    /// Get local participant list for a room (excludes federated virtual participants).
+    pub fn local_participants(&self, room_name: &str) -> Vec<wzp_proto::packet::RoomParticipant> {
+        self.rooms.get(room_name)
+            .map(|room| room.participants.iter()
+                .filter(|p| p.origin == ParticipantOrigin::Local)
+                .map(|p| wzp_proto::packet::RoomParticipant {
+                    fingerprint: p.fingerprint.clone().unwrap_or_default(),
+                    alias: p.alias.clone(),
+                })
+                .collect())
+            .unwrap_or_default()
+    }
+
+    /// Get senders for local-only participants in a room (for federation inbound media).
+    pub fn local_senders(&self, room_name: &str) -> Vec<ParticipantSender> {
+        self.rooms.get(room_name)
+            .map(|room| room.participants.iter()
+                .filter(|p| p.origin == ParticipantOrigin::Local)
+                .map(|p| p.sender.clone())
+                .collect())
+            .unwrap_or_default()
+    }
+
     /// Leave a room. Returns (room_update_msg, remaining_senders) for broadcasting, or None if room is now empty.
     pub fn leave(&mut self, room_name: &str, participant_id: ParticipantId) -> Option<(wzp_proto::SignalMessage, Vec<ParticipantSender>)> {
         if let Some(room) = self.rooms.get_mut(room_name) {
@@ -467,6 +594,19 @@ async fn run_participant_plain(
                 ParticipantSender::WebSocket(_) => {
                     let _ = other.send_raw(&pkt.payload).await;
                 }
+                ParticipantSender::Federation { transport, room_hash } => {
+                    // Send room-tagged datagram to federated peer
+                    let data = pkt.to_bytes();
+                    let mut tagged = Vec::with_capacity(8 + data.len());
+                    tagged.extend_from_slice(room_hash);
+                    tagged.extend_from_slice(&data);
+                    if let Err(e) = transport.send_raw_datagram(&tagged) {
+                        send_errors += 1;
+                        if send_errors <= 5 {
+                            warn!(room = %room_name, "federation forward error: {e}");
+                        }
+                    }
+                }
             }
         }
         let fwd_ms = fwd_start.elapsed().as_millis() as u64;
@@ -634,6 +774,13 @@ async fn run_participant_trunked(
                         ParticipantSender::WebSocket(_) => {
                             let _ = other.send_raw(&pkt.payload).await;
                         }
+                        ParticipantSender::Federation { transport, room_hash } => {
+                            let data = pkt.to_bytes();
+                            let mut tagged = Vec::with_capacity(8 + data.len());
+                            tagged.extend_from_slice(room_hash);
+                            tagged.extend_from_slice(&data);
+                            let _ = transport.send_raw_datagram(&tagged);
+                        }
                     }
                 }
                 let fwd_ms = fwd_start.elapsed().as_millis() as u64;
diff --git a/crates/wzp-transport/src/quic.rs b/crates/wzp-transport/src/quic.rs
index 40c0cea..580d118 100644
--- a/crates/wzp-transport/src/quic.rs
+++ b/crates/wzp-transport/src/quic.rs
@@ -33,6 +33,13 @@ impl QuinnTransport {
         &self.connection
     }
 
+    /// Send raw bytes as a QUIC datagram (no MediaPacket framing).
+    pub fn send_raw_datagram(&self, data: &[u8]) -> Result<(), TransportError> {
+        self.connection
+            .send_datagram(bytes::Bytes::copy_from_slice(data))
+            .map_err(|e| TransportError::Internal(format!("datagram: {e}")))
+    }
+
     /// Close the QUIC connection immediately (synchronous, no async needed).
     /// The relay will detect the close and remove this participant from the room.
     pub fn close_now(&self) {