diff --git a/Cargo.lock b/Cargo.lock
index 317af86ff..7a00e0de1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5467,6 +5467,7 @@ dependencies = [
  "rustc_version 0.4.1",
  "serde",
  "serde_json",
+ "slab",
  "socket2 0.5.7",
  "tokio",
  "tokio-util",
diff --git a/Cargo.toml b/Cargo.toml
index b5853f489..c33219f46 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -158,6 +158,7 @@ serde = { version = "1.0.210", default-features = false, features = [
 ] } # Default features are disabled due to usage in no_std crates
 serde_json = "1.0.128"
 serde_yaml = "0.9.34"
+slab = "0.4.9"
 static_init = "1.0.3"
 stabby = "36.1.1"
 sha3 = "0.10.8"
diff --git a/zenoh/Cargo.toml b/zenoh/Cargo.toml
index 94f6d6eb4..1bc323095 100644
--- a/zenoh/Cargo.toml
+++ b/zenoh/Cargo.toml
@@ -86,6 +86,7 @@ phf = { workspace = true }
 rand = { workspace = true, features = ["default"] }
 serde = { workspace = true, features = ["default"] }
 serde_json = { workspace = true }
+slab = { workspace = true }
 socket2 = { workspace = true }
 uhlc = { workspace = true, features = ["default"] }
 vec_map = { workspace = true }
diff --git a/zenoh/src/net/routing/dispatcher/face.rs b/zenoh/src/net/routing/dispatcher/face.rs
index 6e1db6bbf..0b3078a80 100644
--- a/zenoh/src/net/routing/dispatcher/face.rs
+++ b/zenoh/src/net/routing/dispatcher/face.rs
@@ -19,12 +19,13 @@ use std::{
     time::Duration,
 };
 
+use slab::Slab;
 use tokio_util::sync::CancellationToken;
 use zenoh_protocol::{
     core::{ExprId, Reliability, WhatAmI, ZenohIdProto},
     network::{
         interest::{InterestId, InterestMode, InterestOptions},
-        Mapping, Push, Request, RequestId, Response, ResponseFinal,
+        Mapping, Push, Request, Response, ResponseFinal,
     },
     zenoh::RequestBody,
 };
@@ -70,8 +71,7 @@ pub struct FaceState {
         HashMap<InterestId, (Arc<CurrentInterest>, CancellationToken)>,
     pub(crate) local_mappings: HashMap<ExprId, Arc<Resource>>,
     pub(crate) remote_mappings: HashMap<ExprId, Arc<Resource>>,
-    pub(crate) next_qid: RequestId,
-    pub(crate) pending_queries: HashMap<RequestId, (Arc<Query>, CancellationToken)>,
+    pub(crate) pending_queries: Slab<(Arc<Query>, CancellationToken)>,
     pub(crate) mcast_group: Option<TransportMulticast>,
     pub(crate) in_interceptors: Option<Arc<InterceptorsChain>>,
     pub(crate) hat: Box<dyn Any + Send + Sync>,
@@ -102,8 +102,7 @@ impl FaceState {
             pending_current_interests: HashMap::new(),
             local_mappings: HashMap::new(),
             remote_mappings: HashMap::new(),
-            next_qid: 0,
-            pending_queries: HashMap::new(),
+            pending_queries: Slab::new(),
             mcast_group,
             in_interceptors,
             hat,
diff --git a/zenoh/src/net/routing/dispatcher/queries.rs b/zenoh/src/net/routing/dispatcher/queries.rs
index f8a9f1f12..e62a912c4 100644
--- a/zenoh/src/net/routing/dispatcher/queries.rs
+++ b/zenoh/src/net/routing/dispatcher/queries.rs
@@ -290,13 +290,11 @@ pub(crate) fn update_matches_query_routes(tables: &Tables, res: &Arc<Resource>)
 #[inline]
 fn insert_pending_query(outface: &mut Arc<FaceState>, query: Arc<Query>) -> RequestId {
     let outface_mut = get_mut_unchecked(outface);
-    outface_mut.next_qid += 1;
-    let qid = outface_mut.next_qid;
-    outface_mut.pending_queries.insert(
-        qid,
-        (query, outface_mut.task_controller.get_cancellation_token()),
-    );
-    qid
+    outface_mut
+        .pending_queries
+        .insert((query, outface_mut.task_controller.get_cancellation_token()))
+        .try_into()
+        .expect("too many pending queries")
 }
 
 #[inline]
@@ -381,7 +379,7 @@ impl QueryCleanup {
             qid,
             timeout,
         };
-        if let Some((_, cancellation_token)) = face.pending_queries.get(&qid) {
+        if let Some((_, cancellation_token)) = face.pending_queries.get(qid as usize) {
             let c_cancellation_token = cancellation_token.clone();
             face.task_controller
                 .spawn_with_rt(zenoh_runtime::ZRuntime::Net, async move {
@@ -422,7 +420,7 @@ impl Timed for QueryCleanup {
             let queries_lock = zwrite!(self.tables.queries_lock);
             if let Some(query) = get_mut_unchecked(&mut face)
                 .pending_queries
-                .remove(&self.qid)
+                .try_remove(self.qid as usize)
             {
                 drop(queries_lock);
                 tracing::warn!(
@@ -682,7 +680,7 @@ pub(crate) fn route_send_response(
         inc_res_stats!(face, rx, admin, body)
     }
 
-    match face.pending_queries.get(&qid) {
+    match face.pending_queries.get(qid as usize) {
         Some((query, _)) => {
             drop(queries_lock);
 
@@ -717,7 +715,10 @@ pub(crate) fn route_send_response_final(
     qid: RequestId,
 ) {
     let queries_lock = zwrite!(tables_ref.queries_lock);
-    match get_mut_unchecked(face).pending_queries.remove(&qid) {
+    match get_mut_unchecked(face)
+        .pending_queries
+        .try_remove(qid as usize)
+    {
         Some(query) => {
             drop(queries_lock);
             tracing::debug!(
@@ -735,7 +736,7 @@ pub(crate) fn route_send_response_final(
 
 pub(crate) fn finalize_pending_queries(tables_ref: &TablesLock, face: &mut Arc<FaceState>) {
     let queries_lock = zwrite!(tables_ref.queries_lock);
-    for (_, query) in get_mut_unchecked(face).pending_queries.drain() {
+    for query in get_mut_unchecked(face).pending_queries.drain() {
         finalize_pending_query(query);
     }
     drop(queries_lock);
diff --git a/zenoh/src/net/runtime/mod.rs b/zenoh/src/net/runtime/mod.rs
index 301698eea..225b7e64a 100644
--- a/zenoh/src/net/runtime/mod.rs
+++ b/zenoh/src/net/runtime/mod.rs
@@ -70,7 +70,7 @@ use crate::{
 pub(crate) struct RuntimeState {
     zid: ZenohId,
     whatami: WhatAmI,
-    next_id: AtomicU32,
+    next_id: AtomicU32, // @TODO: manage rollover and uniqueness
     router: Arc<Router>,
     config: Notifier<Config>,
     manager: TransportManager,