diff --git a/Cargo.lock b/Cargo.lock
index 69bb23c9af..9fdb238265 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -8582,6 +8582,11 @@ checksum = "a156c684c91ea7d62626509bce3cb4e1d9ed5c4d978f7b4352658f96a4c26b4a"
 [[package]]
 name = "unused_port"
 version = "0.1.0"
+dependencies = [
+ "lazy_static",
+ "lru_cache",
+ "parking_lot 0.12.1",
+]
 
 [[package]]
 name = "url"
diff --git a/book/src/database-migrations.md b/book/src/database-migrations.md
index ef7e95cc7a..d2b7b518d7 100644
--- a/book/src/database-migrations.md
+++ b/book/src/database-migrations.md
@@ -28,6 +28,7 @@ validator client or the slasher**.
 | v3.3.0             | Nov 2022     | v13            | yes                  |
 | v3.4.0             | Jan 2023     | v13            | yes                  |
 | v3.5.0             | Feb 2023     | v15            | yes before Capella   |
+| v4.0.1             | Mar 2023     | v16            | yes before Capella   |
 
 > **Note**: All point releases (e.g. v2.3.1) are schema-compatible with the prior minor release
 > (e.g. v2.3.0).
diff --git a/common/unused_port/Cargo.toml b/common/unused_port/Cargo.toml
index 06c1ca8f58..2dd041ff07 100644
--- a/common/unused_port/Cargo.toml
+++ b/common/unused_port/Cargo.toml
@@ -6,3 +6,6 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+lru_cache = { path = "../lru_cache" }
+lazy_static = "1.4.0"
+parking_lot = "0.12.0"
diff --git a/common/unused_port/src/lib.rs b/common/unused_port/src/lib.rs
index a5d0817211..386f08a739 100644
--- a/common/unused_port/src/lib.rs
+++ b/common/unused_port/src/lib.rs
@@ -1,4 +1,8 @@
-use std::net::{TcpListener, UdpSocket};
+use lazy_static::lazy_static;
+use lru_cache::LRUTimeCache;
+use parking_lot::Mutex;
+use std::net::{SocketAddr, TcpListener, UdpSocket};
+use std::time::Duration;
 
 #[derive(Copy, Clone)]
 pub enum Transport {
@@ -12,6 +16,13 @@ pub enum IpVersion {
     Ipv6,
 }
 
+pub const CACHED_PORTS_TTL: Duration = Duration::from_secs(300);
+
+lazy_static! {
+    static ref FOUND_PORTS_CACHE: Mutex<LRUTimeCache<u16>> =
+        Mutex::new(LRUTimeCache::new(CACHED_PORTS_TTL));
+}
+
 /// A convenience wrapper over [`zero_port`].
 pub fn unused_tcp4_port() -> Result<u16, String> {
     zero_port(Transport::Tcp, IpVersion::Ipv4)
@@ -48,6 +59,20 @@ pub fn zero_port(transport: Transport, ipv: IpVersion) -> Result<u16, String> {
         IpVersion::Ipv6 => std::net::Ipv6Addr::LOCALHOST.into(),
     };
     let socket_addr = std::net::SocketAddr::new(localhost, 0);
+    let mut unused_port: u16;
+    loop {
+        unused_port = find_unused_port(transport, socket_addr)?;
+        let mut cache_lock = FOUND_PORTS_CACHE.lock();
+        if !cache_lock.contains(&unused_port) {
+            cache_lock.insert(unused_port);
+            break;
+        }
+    }
+
+    Ok(unused_port)
+}
+
+fn find_unused_port(transport: Transport, socket_addr: SocketAddr) -> Result<u16, String> {
     let local_addr = match transport {
         Transport::Tcp => {
             let listener = TcpListener::bind(socket_addr).map_err(|e| {
diff --git a/scripts/local_testnet/README.md b/scripts/local_testnet/README.md
index c9fb387681..c4050ac934 100644
--- a/scripts/local_testnet/README.md
+++ b/scripts/local_testnet/README.md
@@ -20,7 +20,7 @@ Modify `vars.env` as desired.
 Start a local eth1 ganache server plus boot node along with `BN_COUNT`
 number of beacon nodes and `VC_COUNT` validator clients.
 
-The `start_local_testnet.sh` script takes three options `-v VC_COUNT`, `-d DEBUG_LEVEL` and `-h` for help.
+The `start_local_testnet.sh` script takes four options `-v VC_COUNT`, `-d DEBUG_LEVEL`, `-p` to enable builder proposals and `-h` for help.
 The options may be in any order or absent in which case they take the default value specified.
 - VC_COUNT: the number of validator clients to create, default: `BN_COUNT`
 - DEBUG_LEVEL: one of { error, warn, info, debug, trace }, default: `info`
diff --git a/scripts/local_testnet/start_local_testnet.sh b/scripts/local_testnet/start_local_testnet.sh
index a188a1458b..ce36966e27 100755
--- a/scripts/local_testnet/start_local_testnet.sh
+++ b/scripts/local_testnet/start_local_testnet.sh
@@ -28,7 +28,7 @@ while getopts "v:d:ph" flag; do
         echo "Options:"
         echo "   -v: VC_COUNT    default: $VC_COUNT"
         echo "   -d: DEBUG_LEVEL default: info"
-        echo "   -p:             enable private tx proposals"
+        echo "   -p:             enable builder proposals"
         echo "   -h:             this help"
         exit
         ;;