Merge pull request #884 from vgrebenschikov/feature/synlimit-pf-support

Add PF synlimit backend

docs/Config_params/CONFIG_PARAMS.en.md

@@ -2311,7 +2311,7 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
 | [`ip`](#ip) | `IpAddr` | — | `✘` |
 | [`port`](#port-serverlisteners) | `u16` | `server.port` | `✘` |
 | [`client_mss`](#client_mss-serverlisteners) | `String` | `[server].client_mss` | `✘` |
-| [`synlimit`](#synlimit-serverlisteners) | `false`, `"iptables"`, or `"nftables"` | `false` | `✔` |
+| [`synlimit`](#synlimit-serverlisteners) | `false`, `"iptables"`, `"nftables"`, or `"pf"` | `false` | `✔` |
 | [`synlimit_seconds`](#synlimit_seconds-serverlisteners) | `u32` | `60` | `✔` |
 | [`synlimit_hitcount`](#synlimit_hitcount-serverlisteners) | `u32` | `48` | `✔` |
 | [`synlimit_burst`](#synlimit_burst-serverlisteners) | `u32` | `1` | `✔` |
@@ -2356,8 +2356,8 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
     client_mss = "256"
     ```
 ## synlimit (server.listeners)
-  - **Constraints / validation**: `false`, `"iptables"`, or `"nftables"`. Omitted or `false` disables SYN limiting for this listener.
-  - **Description**: Installs per-listener Linux netfilter two-tier SYN-fix rules for the listener port. `"iptables"` uses `iptables`/`ip6tables` filter rules with the `hashlimit`, `length`, and TTL/hop-limit matches. `"nftables"` uses Telemt-owned tables with per-source `meter` rules and equivalent IPv4/IPv6 classifiers. Rules are inserted early in `INPUT`, accept under-limit SYN packets, and reject over-limit SYN packets with TCP RST so clients retry promptly instead of waiting for a silent DROP timeout. The generic bucket is controlled by `synlimit_seconds`, `synlimit_hitcount`, and `synlimit_burst`; the iOS-like TTL/length bucket is controlled by `synlimit_ios_*`. Rules are reconciled at runtime and removed during graceful Telemt shutdown; `SIGKILL` cannot be cleaned up by the process. Requires CAP_NET_ADMIN. `synlimit*` changes hot-reload for existing listener endpoints; changing listener `ip` or `port` still requires restart/rebind.
+  - **Constraints / validation**: `false`, `"iptables"`, `"nftables"`, or `"pf"`. Omitted or `false` disables SYN limiting for this listener.
+  - **Description**: Installs per-listener firewall rules for the listener port. `"iptables"` uses Linux `iptables`/`ip6tables` filter rules with the `hashlimit`, `length`, and TTL/hop-limit matches. `"nftables"` uses Linux Telemt-owned tables with per-source `meter` rules and equivalent IPv4/IPv6 classifiers. These Linux rules are inserted early in `INPUT`, accept under-limit SYN packets, and reject over-limit SYN packets with TCP RST so clients retry promptly instead of waiting for a silent DROP timeout. `"pf"` uses FreeBSD PF source tracking in a Telemt anchor with `max-src-conn-rate`; PF applies this rate after TCP three-way handshake completion, accepts under-limit connections, and rejects over-limit new connections until the source rate falls back below the configured window. The generic bucket is controlled by `synlimit_seconds`, `synlimit_hitcount`, and `synlimit_burst` on Linux; PF maps `synlimit_hitcount / synlimit_seconds` to `max-src-conn-rate` and has no direct equivalents for `synlimit_burst`, `synlimit_ios_*`, or `synlimit_hashlimit_*`. Rules are reconciled at runtime and removed during graceful Telemt shutdown; `SIGKILL` cannot be cleaned up by the process. Linux requires CAP_NET_ADMIN. FreeBSD requires root and a main PF ruleset hook such as `anchor "telemt_synlimit/*"`. `synlimit*` changes hot-reload for existing listener endpoints; changing listener `ip` or `port` still requires restart/rebind.
   - **Operator note**: Telemt does not persist rules with `iptables-persistent`, write `/etc/sysctl.d`, edit systemd limits, or modify `client_mss`. Apply host-level tuning manually if your deployment policy requires it.
   - **Example**:
 
@@ -2371,10 +2371,15 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
     ip = "::"
     port = 443
     synlimit = "nftables"
+
+    [[server.listeners]]
+    ip = "0.0.0.0"
+    port = 443
+    synlimit = "pf"
     ```
 ## synlimit_seconds (server.listeners)
   - **Constraints / validation**: `u32`, must be `> 0`. Default is `60`.
-  - **Description**: Generic SYN-fix token-bucket interval. The rate is `synlimit_hitcount / synlimit_seconds` and is rendered to native netfilter rate units (`second`, `minute`, `hour`, or `day`). This bucket handles SYN packets that do not match the iOS-like TTL/length classifier.
+  - **Description**: Generic SYN-fix token-bucket interval. For Linux backends, the rate is `synlimit_hitcount / synlimit_seconds` and is rendered to native netfilter rate units (`second`, `minute`, `hour`, or `day`). This bucket handles SYN packets that do not match the iOS-like TTL/length classifier. For PF, the same pair is rendered as `max-src-conn-rate hitcount/seconds`.
   - **Example**:
 
     ```toml
@@ -2446,7 +2451,7 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
     ```
 ## synlimit_hashlimit_expire_ms (server.listeners)
   - **Constraints / validation**: `u32`, must be `> 0`. Default is `60000`.
-  - **Description**: Entry expiration in milliseconds for iptables/ip6tables hashlimit buckets. nftables meters use kernel-managed state and do not expose this exact knob.
+  - **Description**: Entry expiration in milliseconds for iptables/ip6tables hashlimit buckets. nftables meters and PF source tracking use kernel-managed state and do not expose this exact knob.
   - **Example**:
 
     ```toml
@@ -2458,7 +2463,7 @@ Note: This section also accepts the legacy alias `[server.admin_api]` (same sche
     ```
 ## synlimit_hashlimit_size (server.listeners)
   - **Constraints / validation**: `u32`, must be `> 0`. Default is `32768`.
-  - **Description**: Hash table size for iptables/ip6tables hashlimit buckets. nftables meters use kernel-managed state and do not expose this exact knob.
+  - **Description**: Hash table size for iptables/ip6tables hashlimit buckets. nftables meters and PF source tracking use kernel-managed state and do not expose this exact knob.
   - **Example**:
 
     ```toml

src/config/tests/load_basic_tests.rs

@@ -62,6 +62,26 @@ fn synlimit_synfix_defaults_are_loaded_for_listener() {
     assert_eq!(listener.synlimit_hashlimit_size, 32_768);
 }
 
+#[test]
+fn synlimit_pf_mode_is_loaded_for_listener() {
+    let cfg = load_config_from_temp_toml(
+        r#"
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+
+            [[server.listeners]]
+            ip = "0.0.0.0"
+            port = 443
+            synlimit = "pf"
+        "#,
+    );
+
+    assert_eq!(cfg.server.listeners[0].synlimit, SynLimitMode::Pf);
+}
+
 #[test]
 fn synlimit_synfix_zero_values_are_rejected() {
     for (field, expected) in [

src/config/types.rs

@@ -1471,6 +1471,8 @@ pub enum SynLimitMode {
     Iptables,
     /// Use nftables two-tier SYN-fix rules with per-source token-bucket meters.
     Nftables,
+    /// Use FreeBSD PF source tracking with connection-rate state limits.
+    Pf,
 }
 
 impl Serialize for SynLimitMode {
@@ -1482,6 +1484,7 @@ impl Serialize for SynLimitMode {
             Self::Off => serializer.serialize_bool(false),
             Self::Iptables => serializer.serialize_str("iptables"),
             Self::Nftables => serializer.serialize_str("nftables"),
+            Self::Pf => serializer.serialize_str("pf"),
         }
     }
 }
@@ -1497,7 +1500,7 @@ impl<'de> Deserialize<'de> for SynLimitMode {
             type Value = SynLimitMode;
 
             fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-                formatter.write_str("false, iptables, or nftables")
+                formatter.write_str("false, iptables, nftables, or pf")
             }
 
             fn visit_bool<E>(self, value: bool) -> std::result::Result<Self::Value, E>
@@ -1506,7 +1509,7 @@ impl<'de> Deserialize<'de> for SynLimitMode {
             {
                 if value {
                     Err(E::custom(
-                        "synlimit=true is ambiguous; use \"iptables\" or \"nftables\"",
+                        "synlimit=true is ambiguous; use \"iptables\", \"nftables\", or \"pf\"",
                     ))
                 } else {
                     Ok(SynLimitMode::Off)
@@ -1521,8 +1524,9 @@ impl<'de> Deserialize<'de> for SynLimitMode {
                     "false" | "off" | "disabled" | "none" => Ok(SynLimitMode::Off),
                     "iptables" => Ok(SynLimitMode::Iptables),
                     "nftables" => Ok(SynLimitMode::Nftables),
+                    "pf" => Ok(SynLimitMode::Pf),
                     _ => Err(E::custom(
-                        "synlimit must be false, \"iptables\", or \"nftables\"",
+                        "synlimit must be false, \"iptables\", \"nftables\", or \"pf\"",
                     )),
                 }
             }

src/maestro/mod.rs

@@ -987,7 +987,9 @@ async fn run_telemt_core(
         std::process::exit(1);
     }
 
-    // On Unix, caller supplies privilege drop after bind (may require root for port < 1024).
+    synlimit_control::reconcile_synlimit_rules(&config).await;
+
+    // On Unix, caller supplies privilege drop after bind and privileged firewall setup.
     drop_after_bind();
 
     let synlimit_controller = synlimit_control::spawn_synlimit_controller(runtime_watch_rx);

src/synlimit_control/command.rs

@@ -74,7 +74,7 @@ fn resolve_command(binary: &str) -> Option<PathBuf> {
         .find(|candidate| candidate.exists() && candidate.is_file())
 }
 
-pub(super) fn has_cap_net_admin() -> bool {
+pub(super) fn has_firewall_privileges() -> bool {
     #[cfg(target_os = "linux")]
     {
         let Ok(status) = std::fs::read_to_string("/proc/self/status") else {
@@ -91,7 +91,11 @@ pub(super) fn has_cap_net_admin() -> bool {
         }
         false
     }
-    #[cfg(not(target_os = "linux"))]
+    #[cfg(all(unix, not(target_os = "linux")))]
+    {
+        nix::unistd::Uid::effective().is_root()
+    }
+    #[cfg(not(unix))]
     {
         false
     }

src/synlimit_control/iptables.rs

@@ -321,6 +321,7 @@ mod tests {
             nft_table: "telemt_synlimit_test".to_string(),
             iptables_chain: "TMT_SYN_TEST".to_string(),
             iptables_hashlimit_prefix: "TMTTEST".to_string(),
+            pf_anchor: "telemt_synlimit/test".to_string(),
         }
     }
 

src/synlimit_control/mod.rs

@@ -4,15 +4,16 @@ use tokio::sync::watch;
 use tokio_util::sync::CancellationToken;
 use tracing::warn;
 
-use crate::config::{ProxyConfig, SynLimitMode};
+use crate::config::ProxyConfig;
 use crate::maestro::generation::RuntimeWatchState;
 
 mod command;
 mod iptables;
 mod model;
 mod nftables;
+mod pf;
 
-use self::command::has_cap_net_admin;
+use self::command::has_firewall_privileges;
 use self::model::{SynLimitNamespace, synlimit_namespace, synlimit_targets};
 
 static ACTIVE_SYNLIMIT_NAMESPACE: Mutex<Option<SynLimitNamespace>> = Mutex::new(None);
@@ -36,27 +37,13 @@ pub(crate) fn spawn_synlimit_controller(
     runtime_watch_rx: watch::Receiver<Option<RuntimeWatchState>>,
 ) -> SynlimitController {
     let shutdown = CancellationToken::new();
-    let join = if !cfg!(target_os = "linux") {
-        tokio::spawn(watch_active_runtime_configs(
-            runtime_watch_rx,
-            shutdown.clone(),
-            |_generation_id, cfg| async move {
-                if has_synlimit_config(&cfg) {
-                    warn!(
-                        "SYN limiter is configured but unsupported on this OS; skipping netfilter rules"
-                    );
-                }
-            },
-        ))
-    } else {
-        tokio::spawn(watch_active_runtime_configs(
-            runtime_watch_rx,
-            shutdown.clone(),
-            |_generation_id, cfg| async move {
-                reconcile_synlimit_rules(&cfg).await;
-            },
-        ))
-    };
+    let join = tokio::spawn(watch_active_runtime_configs(
+        runtime_watch_rx,
+        shutdown.clone(),
+        |_generation_id, cfg| async move {
+            reconcile_synlimit_rules(&cfg).await;
+        },
+    ));
     SynlimitController { shutdown, join }
 }
 
@@ -176,10 +163,8 @@ pub(crate) async fn reconcile_synlimit_rules(cfg: &ProxyConfig) {
     let Some(namespace) = namespace else {
         return;
     };
-    if !has_cap_net_admin() {
-        warn!(
-            "SYN limiter configured but CAP_NET_ADMIN is not available; netfilter rules not applied"
-        );
+    if !has_firewall_privileges() {
+        warn!("SYN limiter configured but firewall privileges are not available; rules not applied");
         return;
     }
 
@@ -193,15 +178,20 @@ pub(crate) async fn reconcile_synlimit_rules(cfg: &ProxyConfig) {
         }
     }
 
-    if targets.has_iptables_targets()
-        && let Err(error) = iptables::apply_synlimit_rules(&targets, &namespace).await
-    {
-        warn!(error = %error, "Failed to apply iptables SYN limiter rules");
+    if targets.has_iptables_targets() {
+        if let Err(error) = iptables::apply_synlimit_rules(&targets, &namespace).await {
+            warn!(error = %error, "Failed to apply iptables SYN limiter rules");
+        }
     }
-    if targets.has_nft_targets()
-        && let Err(error) = nftables::apply_synlimit_rules(&targets, &namespace).await
-    {
-        warn!(error = %error, "Failed to apply nftables SYN limiter rules");
+    if targets.has_nft_targets() {
+        if let Err(error) = nftables::apply_synlimit_rules(&targets, &namespace).await {
+            warn!(error = %error, "Failed to apply nftables SYN limiter rules");
+        }
+    }
+    if targets.has_pf_targets() {
+        if let Err(error) = pf::apply_synlimit_rules(&targets, &namespace).await {
+            warn!(error = %error, "Failed to apply PF SYN limiter rules");
+        }
     }
 }
 
@@ -213,7 +203,7 @@ pub(crate) async fn clear_synlimit_rules_all_backends() -> Result<bool, String>
 }
 
 async fn clear_synlimit_rules_for_namespace(namespace: &SynLimitNamespace) -> Result<bool, String> {
-    if !has_cap_net_admin() {
+    if !has_firewall_privileges() {
         return Ok(false);
     }
 
@@ -243,6 +233,14 @@ async fn clear_synlimit_rules_for_namespace(namespace: &SynLimitNamespace) -> Re
             errors.push(error);
         }
     }
+    match pf::clear_rules(namespace).await {
+        Ok(value) => {
+            removed |= value;
+        }
+        Err(error) => {
+            errors.push(error);
+        }
+    }
 
     if errors.is_empty() {
         Ok(removed)
@@ -277,13 +275,6 @@ fn take_active_synlimit_namespace() -> Option<SynLimitNamespace> {
     }
 }
 
-fn has_synlimit_config(cfg: &ProxyConfig) -> bool {
-    cfg.server
-        .listeners
-        .iter()
-        .any(|listener| !matches!(listener.synlimit, SynLimitMode::Off))
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;

src/synlimit_control/model.rs

@@ -22,6 +22,7 @@ pub(super) struct SynLimitNamespace {
     pub(super) nft_table: String,
     pub(super) iptables_chain: String,
     pub(super) iptables_hashlimit_prefix: String,
+    pub(super) pf_anchor: String,
 }
 
 #[derive(Default)]
@@ -30,6 +31,8 @@ pub(super) struct SynLimitTargets {
     pub(super) iptables_v6: Vec<SynLimitRule>,
     pub(super) nft_v4: Vec<SynLimitRule>,
     pub(super) nft_v6: Vec<SynLimitRule>,
+    pub(super) pf_v4: Vec<SynLimitRule>,
+    pub(super) pf_v6: Vec<SynLimitRule>,
 }
 
 impl SynLimitTargets {
@@ -38,6 +41,8 @@ impl SynLimitTargets {
             && self.iptables_v6.is_empty()
             && self.nft_v4.is_empty()
             && self.nft_v6.is_empty()
+            && self.pf_v4.is_empty()
+            && self.pf_v6.is_empty()
     }
 
     pub(super) fn has_iptables_targets(&self) -> bool {
@@ -47,6 +52,10 @@ impl SynLimitTargets {
     pub(super) fn has_nft_targets(&self) -> bool {
         !self.nft_v4.is_empty() || !self.nft_v6.is_empty()
     }
+
+    pub(super) fn has_pf_targets(&self) -> bool {
+        !self.pf_v4.is_empty() || !self.pf_v6.is_empty()
+    }
 }
 
 struct SynLimitNamespaceHasher {
@@ -92,6 +101,8 @@ pub(super) fn synlimit_targets(cfg: &ProxyConfig) -> SynLimitTargets {
     let mut iptables_v6 = BTreeSet::new();
     let mut nft_v4 = BTreeSet::new();
     let mut nft_v6 = BTreeSet::new();
+    let mut pf_v4 = BTreeSet::new();
+    let mut pf_v6 = BTreeSet::new();
 
     for listener in &cfg.server.listeners {
         let backend = listener.synlimit;
@@ -124,6 +135,12 @@ pub(super) fn synlimit_targets(cfg: &ProxyConfig) -> SynLimitTargets {
             (SynLimitMode::Nftables, false) => {
                 nft_v6.insert(target);
             }
+            (SynLimitMode::Pf, true) => {
+                pf_v4.insert(target);
+            }
+            (SynLimitMode::Pf, false) => {
+                pf_v6.insert(target);
+            }
             (SynLimitMode::Off, _) => {}
         }
     }
@@ -133,6 +150,8 @@ pub(super) fn synlimit_targets(cfg: &ProxyConfig) -> SynLimitTargets {
         iptables_v6: iptables_v6.into_iter().collect(),
         nft_v4: nft_v4.into_iter().collect(),
         nft_v6: nft_v6.into_iter().collect(),
+        pf_v4: pf_v4.into_iter().collect(),
+        pf_v6: pf_v6.into_iter().collect(),
     }
 }
 
@@ -146,6 +165,8 @@ pub(super) fn synlimit_namespace(targets: &SynLimitTargets) -> Option<SynLimitNa
     write_namespace_rule_group(&mut hasher, b"iptables-v6", &targets.iptables_v6);
     write_namespace_rule_group(&mut hasher, b"nft-v4", &targets.nft_v4);
     write_namespace_rule_group(&mut hasher, b"nft-v6", &targets.nft_v6);
+    write_namespace_rule_group(&mut hasher, b"pf-v4", &targets.pf_v4);
+    write_namespace_rule_group(&mut hasher, b"pf-v6", &targets.pf_v6);
 
     let suffix = format!("{:016x}", hasher.finish());
     let iptables_suffix = &suffix[..12];
@@ -154,6 +175,7 @@ pub(super) fn synlimit_namespace(targets: &SynLimitTargets) -> Option<SynLimitNa
         nft_table: format!("telemt_synlimit_{suffix}"),
         iptables_chain: format!("TMT_SYN_{iptables_suffix}"),
         iptables_hashlimit_prefix: format!("TMT{hashlimit_suffix}"),
+        pf_anchor: format!("telemt_synlimit/{suffix}"),
     })
 }
 
@@ -307,6 +329,16 @@ mod tests {
                 Some(444),
                 SynLimitMode::Nftables,
             ),
+            listener(
+                IpAddr::V4(Ipv4Addr::new(203, 0, 113, 3)),
+                Some(445),
+                SynLimitMode::Pf,
+            ),
+            listener(
+                IpAddr::V6(Ipv6Addr::UNSPECIFIED),
+                Some(445),
+                SynLimitMode::Pf,
+            ),
         ];
 
         let targets = synlimit_targets(&cfg);
@@ -315,6 +347,8 @@ mod tests {
         assert_eq!(targets.iptables_v6.len(), 1);
         assert_eq!(targets.nft_v4.len(), 1);
         assert_eq!(targets.nft_v6.len(), 1);
+        assert_eq!(targets.pf_v4.len(), 1);
+        assert_eq!(targets.pf_v6.len(), 1);
         assert_eq!(
             targets.iptables_v4[0].ip,
             Some(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 1)))
@@ -328,6 +362,11 @@ mod tests {
             Some(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 2)))
         );
         assert_eq!(targets.nft_v6[0].ip, None);
+        assert_eq!(
+            targets.pf_v4[0].ip,
+            Some(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 3)))
+        );
+        assert_eq!(targets.pf_v6[0].ip, None);
     }
 
     #[test]
@@ -353,6 +392,7 @@ mod tests {
         assert!(first.iptables_chain.starts_with("TMT_SYN_"));
         assert!(first.iptables_chain.len() <= 28);
         assert!(first.iptables_hashlimit_prefix.starts_with("TMT"));
+        assert!(first.pf_anchor.starts_with("telemt_synlimit/"));
     }
 
     #[test]

src/synlimit_control/nftables.rs

@@ -236,6 +236,7 @@ mod tests {
             nft_table: table.to_string(),
             iptables_chain: "TMT_SYN_TEST".to_string(),
             iptables_hashlimit_prefix: "TMTTEST".to_string(),
+            pf_anchor: "telemt_synlimit/test".to_string(),
         }
     }
 

src/synlimit_control/pf.rs

@@ -0,0 +1,124 @@
+use std::net::IpAddr;
+
+use super::command::{run_command, run_command_stdout};
+use super::model::{SynLimitNamespace, SynLimitRule, SynLimitTargets};
+
+const PF_ANCHOR_ROOT: &str = "telemt_synlimit";
+
+pub(super) async fn apply_synlimit_rules(
+    targets: &SynLimitTargets,
+    namespace: &SynLimitNamespace,
+) -> Result<(), String> {
+    if !has_pf_anchor_hook().await? {
+        return Err(format!(
+            "PF anchor hook is not installed; add anchor \"{PF_ANCHOR_ROOT}/*\" to pf.conf"
+        ));
+    }
+
+    let script = pf_synlimit_script(targets);
+    run_command("pfctl", &["-a", namespace.pf_anchor.as_str(), "-f", "-"], Some(script)).await
+}
+
+async fn has_pf_anchor_hook() -> Result<bool, String> {
+    let rules = run_command_stdout("pfctl", &["-s", "rules"]).await?;
+    Ok(rules.lines().any(is_pf_anchor_hook_line))
+}
+
+fn is_pf_anchor_hook_line(line: &str) -> bool {
+    line.trim().contains("anchor \"telemt_synlimit/*\"")
+}
+
+fn pf_synlimit_script(targets: &SynLimitTargets) -> String {
+    let mut script = String::new();
+    for target in &targets.pf_v4 {
+        push_pf_rules(&mut script, target);
+    }
+    for target in &targets.pf_v6 {
+        push_pf_rules(&mut script, target);
+    }
+    script
+}
+
+fn push_pf_rules(script: &mut String, target: &SynLimitRule) {
+    let destination = pf_destination(target.ip);
+    script.push_str(&format!(
+        "pass in quick proto tcp from any to {destination} port {port} flags S/SA keep state (max-src-conn-rate {rate}/{seconds})\n",
+        port = target.port,
+        rate = target.generic_hitcount,
+        seconds = target.generic_seconds,
+    ));
+    script.push_str(&format!(
+        "block return-rst in quick proto tcp from any to {destination} port {port}\n",
+        port = target.port,
+    ));
+}
+
+fn pf_destination(ip: Option<IpAddr>) -> String {
+    ip.map(|ip| ip.to_string())
+        .unwrap_or_else(|| "any".to_string())
+}
+
+pub(super) async fn clear_rules(namespace: &SynLimitNamespace) -> Result<bool, String> {
+    match run_command(
+        "pfctl",
+        &["-a", namespace.pf_anchor.as_str(), "-F", "rules"],
+        None,
+    )
+    .await
+    {
+        Ok(()) => Ok(true),
+        Err(error) if is_missing_command_or_pf_anchor(&error) => Ok(false),
+        Err(error) => return Err(format!("pfctl flush anchor rules failed: {error}")),
+    }
+}
+
+fn is_missing_command_or_pf_anchor(error: &str) -> bool {
+    error.contains("pfctl is not available") || error.contains("Anchor does not exist")
+}
+
+#[cfg(test)]
+mod tests {
+    use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+
+    use super::*;
+    use crate::synlimit_control::model::test_rule;
+
+    #[test]
+    fn pf_script_uses_rate_limited_pass_before_reject() {
+        let mut targets = SynLimitTargets::default();
+        targets.pf_v4 = vec![test_rule(Some(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 7))), 443)];
+        let script = pf_synlimit_script(&targets);
+
+        assert!(script.contains(
+            "pass in quick proto tcp from any to 203.0.113.7 port 443 flags S/SA keep state (max-src-conn-rate 48/60)"
+        ));
+        assert!(script.contains(
+            "block return-rst in quick proto tcp from any to 203.0.113.7 port 443"
+        ));
+        let pass_idx = script
+            .find("pass in quick proto tcp from any to 203.0.113.7 port 443")
+            .expect("rate-limited pass rule must be rendered");
+        let block_idx = script
+            .find("block return-rst in quick proto tcp from any to 203.0.113.7 port 443")
+            .expect("reject fallback rule must be rendered");
+        assert!(pass_idx < block_idx);
+    }
+
+    #[test]
+    fn pf_script_supports_wildcard_and_ipv6_destinations() {
+        let mut targets = SynLimitTargets::default();
+        targets.pf_v4 = vec![test_rule(None, 443)];
+        targets.pf_v6 = vec![test_rule(Some(IpAddr::V6(Ipv6Addr::LOCALHOST)), 8443)];
+        let script = pf_synlimit_script(&targets);
+
+        assert!(script.contains("to any port 443"));
+        assert!(script.contains("to ::1 port 8443"));
+    }
+
+    #[test]
+    fn pf_anchor_hook_detection_requires_wildcard_hook() {
+        assert!(is_pf_anchor_hook_line("anchor \"telemt_synlimit/*\" all"));
+        assert!(!is_pf_anchor_hook_line("anchor \"telemt_synlimit\" all"));
+        assert!(!is_pf_anchor_hook_line("anchor \"other\" all"));
+    }
+}