In 8.3 the default TCP keep alive settings introduced in https://github.com/elastic/elasticsearch/pull/59278 are not applied by default, therefore it uses the OS default values. See:

8.3.0:
```
cat connections-8.3.0.txt  | grep -e '930[01]' | head
ESTAB  0       0         [::ffff:127.0.0.1]:46818     [::ffff:127.0.0.1]:9301    timer:(keepalive,119min,0) uid:1038 ino:6837419 sk:a2 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37928     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834869 sk:a3 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46808   timer:(keepalive,119min,0) uid:1038 ino:6830957 sk:a4 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37942     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834871 sk:a5 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46828   timer:(keepalive,119min,0) uid:1038 ino:6834882 sk:a6 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37926     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834868 sk:a7 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46826   timer:(keepalive,119min,0) uid:1038 ino:6834881 sk:a8 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46824     [::ffff:127.0.0.1]:9301    timer:(keepalive,119min,0) uid:1038 ino:6837425 sk:a9 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37944     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834879 sk:aa <->
ESTAB  0       0         [::ffff:127.0.0.1]:46828     [::ffff:127.0.0.1]:9301    timer:(keepalive,119min,0) uid:1038 ino:6837430 sk:ab <->
```

8.2.2:
```
cat connections-8.2.2.txt  | grep -e '930[01]' | head
ESTAB  0       0         [::ffff:127.0.0.1]:46752     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833637 sk:6e <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46746   timer:(keepalive,4min52sec,0) uid:1038 ino:6831684 sk:6f <->
ESTAB  0       0         [::ffff:127.0.0.1]:46732     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833629 sk:70 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37876     [::ffff:127.0.0.1]:9300    timer:(keepalive,4min52sec,0) uid:1038 ino:6833618 sk:71 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46730   timer:(keepalive,4min52sec,0) uid:1038 ino:6831676 sk:72 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46748     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833640 sk:73 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46736     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833631 sk:74 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46732   timer:(keepalive,4min52sec,0) uid:1038 ino:6831677 sk:75 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37860     [::ffff:127.0.0.1]:9300    timer:(keepalive,4min52sec,0) uid:1038 ino:6833611 sk:76 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46734     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833630 sk:77 <->
```

It's possible that after moving `NetUtil` to the netty module https://github.com/elastic/elasticsearch/pull/85953 some of the internal details used are not available anymore.
modules/transport-netty4/src/test/java/org/elasticsearch/transport/netty4/SimpleNetty4TransportTests.java
};
    }
    public void testConnectException() throws UnknownHostException {
        try {
            connectToNode(
                serviceA,
                new DiscoveryNode(
                    "C",
                    new TransportAddress(InetAddress.getByName("localhost"), 9876),
                    emptyMap(),
                    emptySet(),
                    Version.CURRENT
                )
            );
            fail("Expected ConnectTransportException");
        } catch (ConnectTransportException e) {
            assertThat(e.getMessage(), containsString("connect_exception"));
            assertThat(e.getMessage(), containsString("[127.0.0.1:9876]"));
        }
    }
    public void testDefaultKeepAliveSettings() throws IOException {
        assumeTrue("setting default keepalive options not supported on this platform", (IOUtils.LINUX || IOUtils.MAC_OS_X));
        try (
            MockTransportService serviceC = buildService("TS_C", Version.CURRENT, Settings.EMPTY);
            MockTransportService serviceD = buildService("TS_D", Version.CURRENT, Settings.EMPTY)
        ) {
            try (Transport.Connection connection = openConnection(serviceC, serviceD.getLocalDiscoNode(), TestProfiles.LIGHT_PROFILE)) {
                assertThat(connection, instanceOf(StubbableTransport.WrappedConnection.class));
                Transport.Connection conn = ((StubbableTransport.WrappedConnection) connection).getConnection();
                assertThat(conn, instanceOf(TcpTransport.NodeChannels.class));