diff --git a/sandboxed_api/sandbox2/BUILD.bazel b/sandboxed_api/sandbox2/BUILD.bazel
index 7a94c20..bac3822 100644
--- a/sandboxed_api/sandbox2/BUILD.bazel
+++ b/sandboxed_api/sandbox2/BUILD.bazel
@@ -89,7 +89,7 @@ cc_library(
         ":syscall",
         ":util",
         "//sandboxed_api/util:status",
-        "@com_google_absl//absl/base",
+        "//sandboxed_api/util:statusor",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/strings",
     ],
@@ -127,36 +127,6 @@ cc_library(
     ],
 )
 
-cc_library(
-    name = "network_proxy_server",
-    srcs = ["network_proxy_server.cc"],
-    hdrs = ["network_proxy_server.h"],
-    copts = sapi_platform_copts(),
-    deps = [
-        ":comms",
-        "//sandboxed_api/sandbox2/util:fileops",
-        "@com_google_absl//absl/memory",
-        "@com_google_glog//:glog",
-    ],
-)
-
-cc_library(
-    name = "network_proxy_client",
-    srcs = ["network_proxy_client.cc"],
-    hdrs = ["network_proxy_client.h"],
-    copts = sapi_platform_copts(),
-    visibility = ["//visibility:public"],
-    deps = [
-        ":comms",
-        "//sandboxed_api/sandbox2/util:strerror",
-        "//sandboxed_api/util:status",
-        "@com_google_absl//absl/memory",
-        "@com_google_absl//absl/strings",
-        "@com_google_absl//absl/synchronization",
-        "@com_google_glog//:glog",
-    ],
-)
-
 cc_library(
     name = "ipc",
     srcs = ["ipc.cc"],
@@ -166,8 +136,6 @@ cc_library(
         ":comms",
         ":logserver",
         ":logsink",
-        ":network_proxy_client",
-        ":network_proxy_server",
         "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/strings",
@@ -186,6 +154,7 @@ cc_library(
         ":regs",
         ":syscall",
         ":violation_cc_proto",
+        "//sandboxed_api/sandbox2/network_proxy:filtering",
         "//sandboxed_api/sandbox2/util:bpf_helper",
         "//sandboxed_api/util:flags",
         "@com_google_absl//absl/base:core_headers",
@@ -306,10 +275,10 @@ cc_library(
         ":client",
         ":executor",
         ":comms",
-        ":violation_cc_proto",
-        ":forkserver",
         ":forkserver_cc_proto",
         ":global_forkserver",
+        ":violation_cc_proto",
+        ":forkserver",
         ":ipc",
         ":limits",
         ":logsink",
@@ -321,7 +290,6 @@ cc_library(
         ":result",
         ":syscall",
         ":util",
-        ":network_proxy_client",
         "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/container:flat_hash_map",
         "@com_google_absl//absl/container:flat_hash_set",
@@ -333,12 +301,17 @@ cc_library(
         "@com_google_absl//absl/time",
         "@com_google_absl//absl/types:optional",
         "@org_kernel_libcap//:libcap",
+        "//sandboxed_api/sandbox2/network_proxy:client",
+        "//sandboxed_api/sandbox2/network_proxy:filtering",
+        "//sandboxed_api/sandbox2/network_proxy:server",
         "//sandboxed_api/sandbox2/unwind",
         "//sandboxed_api/sandbox2/unwind:unwind_cc_proto",
         "//sandboxed_api/sandbox2/util:bpf_helper",
         "//sandboxed_api/sandbox2/util:file_base",
         "//sandboxed_api/sandbox2/util:fileops",
+        "//sandboxed_api/sandbox2/util:strerror",
         "//sandboxed_api/util:raw_logging",
+        "//util/functional",
         "//sandboxed_api/util:status",
         "//sandboxed_api/util:statusor",
 
@@ -364,7 +337,7 @@ cc_library(
     deps = [
         ":comms",
         ":logsink",
-        ":network_proxy_client",
+        "//sandboxed_api/sandbox2/network_proxy:client",
         "//sandboxed_api/sandbox2/util:file_helpers",
         "//sandboxed_api/sandbox2/util:fileops",
         "//sandboxed_api/sandbox2/util:strerror",
diff --git a/sandboxed_api/sandbox2/CMakeLists.txt b/sandboxed_api/sandbox2/CMakeLists.txt
index b2b58fd..fa8c515 100644
--- a/sandboxed_api/sandbox2/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/CMakeLists.txt
@@ -15,6 +15,7 @@
 add_subdirectory(examples)
 add_subdirectory(unwind)
 add_subdirectory(util)
+add_subdirectory(network_proxy)
 
 # sandboxed_api/sandbox2:bpfdisassembler
 add_library(sandbox2_bpfdisassembler STATIC
@@ -121,36 +122,6 @@ target_link_libraries(sandbox2_logsink
   PUBLIC glog::glog
 )
 
-# sandboxed_api/sandbox2:network_proxy_server
-add_library(sandbox2_network_proxy_server STATIC
-  network_proxy_server.cc
-  network_proxy_server.h
-)
-add_library(sandbox2::network_proxy_server ALIAS sandbox2_network_proxy_server)
-target_link_libraries(sandbox2_network_proxy_server PRIVATE
-  absl::memory
-  glog::glog
-  sandbox2::comms
-  sandbox2::fileops
-  sapi::base
-)
-
-# sandboxed_api/sandbox2:network_proxy_client
-add_library(sandbox2_network_proxy_client STATIC
-  network_proxy_client.cc
-  network_proxy_client.h
-)
-add_library(sandbox2::network_proxy_client ALIAS sandbox2_network_proxy_client)
-target_link_libraries(sandbox2_network_proxy_client PRIVATE
-  absl::strings
-  absl::synchronization
-  glog::glog
-  sandbox2::comms
-  sandbox2::strerror
-  sapi::base
-  sapi::status
-)
-
 # sandboxed_api/sandbox2:ipc
 add_library(sandbox2_ipc STATIC
   ipc.cc
diff --git a/sandboxed_api/sandbox2/client.cc b/sandboxed_api/sandbox2/client.cc
index 235ec19..d07c9b1 100644
--- a/sandboxed_api/sandbox2/client.cc
+++ b/sandboxed_api/sandbox2/client.cc
@@ -40,7 +40,6 @@
 #include "absl/strings/str_join.h"
 #include "absl/strings/str_split.h"
 #include "sandboxed_api/sandbox2/comms.h"
-#include "sandboxed_api/sandbox2/network_proxy_client.h"
 #include "sandboxed_api/sandbox2/sanitizer.h"
 #include "sandboxed_api/sandbox2/util/strerror.h"
 #include "sandboxed_api/util/raw_logging.h"
diff --git a/sandboxed_api/sandbox2/client.h b/sandboxed_api/sandbox2/client.h
index d1a4c2c..3518ff8 100644
--- a/sandboxed_api/sandbox2/client.h
+++ b/sandboxed_api/sandbox2/client.h
@@ -25,7 +25,7 @@
 
 #include "sandboxed_api/sandbox2/comms.h"
 #include "sandboxed_api/sandbox2/logsink.h"
-#include "sandboxed_api/sandbox2/network_proxy_client.h"
+#include "sandboxed_api/sandbox2/network_proxy/client.h"
 
 namespace sandbox2 {
 
diff --git a/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel b/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel
index 2a3faed..ad15d87 100644
--- a/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel
+++ b/sandboxed_api/sandbox2/examples/network_proxy/BUILD.bazel
@@ -14,10 +14,10 @@
 
 # The 'network proxy' example demonstrates how to use network proxy server.
 
-licenses(["notice"])
-
 load("//sandboxed_api/bazel:build_defs.bzl", "sapi_platform_copts")
 
+licenses(["notice"])
+
 # Executor
 cc_binary(
     name = "networkproxy_sandbox",
@@ -27,6 +27,7 @@ cc_binary(
     deps = [
         "//sandboxed_api/sandbox2",
         "//sandboxed_api/sandbox2:comms",
+        "//sandboxed_api/sandbox2/network_proxy:filtering",
         "//sandboxed_api/sandbox2/util:bpf_helper",
         "//sandboxed_api/sandbox2/util:fileops",
         "//sandboxed_api/sandbox2/util:runfiles",
@@ -42,7 +43,7 @@ cc_binary(
     deps = [
         "//sandboxed_api/sandbox2:client",
         "//sandboxed_api/sandbox2:comms",
-        "//sandboxed_api/sandbox2:network_proxy_client",
+        "//sandboxed_api/sandbox2/network_proxy:client",
         "//sandboxed_api/sandbox2/util:fileops",
         "@com_google_absl//absl/strings:str_format",
     ],
diff --git a/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_bin.cc b/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_bin.cc
index cd57021..d859f67 100644
--- a/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_bin.cc
+++ b/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_bin.cc
@@ -14,7 +14,7 @@
 #include "absl/strings/str_format.h"
 #include "sandboxed_api/sandbox2/client.h"
 #include "sandboxed_api/sandbox2/comms.h"
-#include "sandboxed_api/sandbox2/network_proxy_client.h"
+#include "sandboxed_api/sandbox2/network_proxy/client.h"
 #include "sandboxed_api/sandbox2/util/fileops.h"
 
 static ssize_t ReadFromFd(int fd, uint8_t* buf, size_t size) {
@@ -113,5 +113,6 @@ int main(int argc, char** argv) {
   if (!CommunicationTest(client.get())) {
     return 4;
   }
+
   return 0;
 }
diff --git a/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc b/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc
index 46aae97..ef80b00 100644
--- a/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc
+++ b/sandboxed_api/sandbox2/examples/network_proxy/networkproxy_sandbox.cc
@@ -42,6 +42,8 @@ std::unique_ptr<sandbox2::Policy> GetPolicy(absl::string_view sandboxee_path) {
       .AllowSyscall(__NR_munmap)
       .AllowSyscall(__NR_getpid)
       .AddNetworkProxyHandlerPolicy()
+      .AllowTcMalloc()
+      .AllowIPv6("::1")
       .AddLibrariesForBinary(sandboxee_path)
       .BuildOrDie();
 }
@@ -129,10 +131,7 @@ int main(int argc, char** argv) {
       // is capable of enabling sandboxing on its own).
       ->set_enable_sandbox_before_exec(false)
       // Set cwd to / to get rids of warnings connected with file namespace.
-      .set_cwd("/")
-      // Enable built-in network proxy.
-      .ipc()
-      ->EnableNetworkProxyServer();
+      .set_cwd("/");
   executor
       ->limits()
       // Remove restrictions on the size of address-space of sandboxed
diff --git a/sandboxed_api/sandbox2/ipc.cc b/sandboxed_api/sandbox2/ipc.cc
index 7c77654..7a25ff5 100644
--- a/sandboxed_api/sandbox2/ipc.cc
+++ b/sandboxed_api/sandbox2/ipc.cc
@@ -17,16 +17,12 @@
 #include "sandboxed_api/sandbox2/ipc.h"
 
 #include <sys/socket.h>
-#include <unistd.h>
-
-#include <thread>  // NOLINT(build/c++11)
+#include <thread>
 
 #include <glog/logging.h>
 #include "absl/memory/memory.h"
 #include "sandboxed_api/sandbox2/logserver.h"
 #include "sandboxed_api/sandbox2/logsink.h"
-#include "sandboxed_api/sandbox2/network_proxy_client.h"
-#include "sandboxed_api/sandbox2/network_proxy_server.h"
 
 namespace sandbox2 {
 
@@ -103,16 +99,4 @@ void IPC::EnableLogServer() {
   log_thread.detach();
 }
 
-void IPC::EnableNetworkProxyServer() {
-  int fd = ReceiveFd(NetworkProxyClient::kFDName);
-
-  auto proxy_server = [fd]() {
-    NetworkProxyServer network_proxy_server(fd);
-    network_proxy_server.Run();
-  };
-
-  std::thread proxy_thread{proxy_server};
-  proxy_thread.detach();
-}
-
 }  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/ipc.h b/sandboxed_api/sandbox2/ipc.h
index 52c4704..69f8421 100644
--- a/sandboxed_api/sandbox2/ipc.h
+++ b/sandboxed_api/sandbox2/ipc.h
@@ -23,7 +23,6 @@
 #include <tuple>
 #include <vector>
 
-#include "absl/base/macros.h"
 #include "absl/strings/string_view.h"
 #include "sandboxed_api/sandbox2/comms.h"
 
@@ -60,10 +59,6 @@ class IPC final {
   // Client::SendLogsToSupervisor in the sandboxee.
   void EnableLogServer();
 
-  // Enable network proxy server, this will start a thread in the sandbox
-  // that waits for connection requests from the sandboxee.
-  void EnableNetworkProxyServer();
-
  private:
   friend class Executor;
   friend class Monitor;
diff --git a/sandboxed_api/sandbox2/monitor.cc b/sandboxed_api/sandbox2/monitor.cc
index 1e62f86..9cc251f 100644
--- a/sandboxed_api/sandbox2/monitor.cc
+++ b/sandboxed_api/sandbox2/monitor.cc
@@ -53,6 +53,7 @@
 #include "sandboxed_api/sandbox2/limits.h"
 #include "sandboxed_api/sandbox2/mounts.h"
 #include "sandboxed_api/sandbox2/namespace.h"
+#include "sandboxed_api/sandbox2/network_proxy/server.h"
 #include "sandboxed_api/sandbox2/policy.h"
 #include "sandboxed_api/sandbox2/regs.h"
 #include "sandboxed_api/sandbox2/result.h"
@@ -140,6 +141,9 @@ Monitor::~Monitor() {
   if (log_file_) {
     std::fclose(log_file_);
   }
+  if (network_proxy_server_) {
+    network_proxy_thread_.join();
+  }
 }
 
 namespace {
@@ -198,6 +202,10 @@ void Monitor::Run() {
   // sandbox master/monitor, which ptrace_attach'es to the child.
   int clone_flags = CLONE_UNTRACED;
 
+  if (policy_->allowed_hosts_) {
+    EnableNetworkProxyServer();
+  }
+
   // Get PID of the sandboxee.
   pid_t init_pid = 0;
   Namespace* ns = policy_->GetNamespace();
@@ -349,6 +357,14 @@ void Monitor::MainLoop(sigset_t* sset) {
       KillSandboxee();
     }
 
+    if (network_proxy_server_ &&
+        network_proxy_server_->violation_occurred_.load(
+            std::memory_order_acquire) &&
+        !network_violation_) {
+      network_violation_ = true;
+      KillSandboxee();
+    }
+
     // It should be a non-blocking operation (hence WNOHANG), so this function
     // returns quickly if there are no events to be processed.
     // Prioritize main pid to avoid resource starvation
@@ -401,7 +417,10 @@ void Monitor::MainLoop(sigset_t* sset) {
       VLOG(1) << "PID: " << ret << " terminated with signal: "
               << util::GetSignalName(WTERMSIG(status));
       if (ret == pid_) {
-        if (external_kill_) {
+        if (network_violation_) {
+          SetExitStatusCode(Result::NETWORK_VIOLATION, 0);
+          result_.SetNetworkViolation(network_proxy_server_->violation_msg_);
+        } else if (external_kill_) {
           SetExitStatusCode(Result::EXTERNAL_KILL, 0);
         } else if (timed_out_) {
           SetExitStatusCode(Result::TIMEOUT, 0);
@@ -794,7 +813,10 @@ void Monitor::EventPtraceExit(pid_t pid, int event_msg) {
   // 3) Regular signal/other exit cause.
   if (pid == pid_) {
     VLOG(1) << "PID: " << pid << " main special exit";
-    if (external_kill_) {
+    if (network_violation_) {
+      SetExitStatusCode(Result::NETWORK_VIOLATION, 0);
+      result_.SetNetworkViolation(network_proxy_server_->violation_msg_);
+    } else if (external_kill_) {
       SetExitStatusCode(Result::EXTERNAL_KILL, 0);
     } else if (timed_out_) {
       SetExitStatusCode(Result::TIMEOUT, 0);
@@ -926,4 +948,14 @@ void Monitor::LogSyscallViolationExplanation(const Syscall& syscall) const {
   }
 }
 
+void Monitor::EnableNetworkProxyServer() {
+  int fd = ipc_->ReceiveFd(NetworkProxyClient::kFDName);
+
+  network_proxy_server_ = absl::make_unique<NetworkProxyServer>(
+      fd, &policy_->allowed_hosts_.value(), pthread_self());
+
+  network_proxy_thread_ = std::thread(&NetworkProxyServer::Run,
+  network_proxy_server_.get());
+}
+
 }  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/monitor.h b/sandboxed_api/sandbox2/monitor.h
index 61358c8..069d93e 100644
--- a/sandboxed_api/sandbox2/monitor.h
+++ b/sandboxed_api/sandbox2/monitor.h
@@ -26,11 +26,13 @@
 #include <cstdio>
 #include <ctime>
 #include <memory>
+#include <thread>
 
 #include "absl/synchronization/notification.h"
 #include "sandboxed_api/sandbox2/comms.h"
 #include "sandboxed_api/sandbox2/executor.h"
 #include "sandboxed_api/sandbox2/ipc.h"
+#include "sandboxed_api/sandbox2/network_proxy/server.h"
 #include "sandboxed_api/sandbox2/notify.h"
 #include "sandboxed_api/sandbox2/policy.h"
 #include "sandboxed_api/sandbox2/regs.h"
@@ -139,6 +141,10 @@ class Monitor final {
   // Processes stop path.
   void EventPtraceStop(pid_t pid, int stopsig);
 
+  // Enable network proxy server, this will start a thread in the sandbox
+  // that waits for connection requests from the sandboxee.
+  void EnableNetworkProxyServer();
+
   // Internal objects, owned by the Sandbox2 object.
   Executor* executor_;
   Notify* notify_;
@@ -168,6 +174,8 @@ class Monitor final {
   std::atomic<int64_t> deadline_millis_{0};
   // Was external kill sent to the sandboxee
   bool external_kill_ = false;
+  // Network violation occurred and process of killing sandboxee started
+  bool network_violation_ = false;
   // Is the sandboxee timed out
   bool timed_out_ = false;
   // Should we dump the main sandboxed PID's stack?
@@ -178,6 +186,12 @@ class Monitor final {
   // Log file specified by
   // --sandbox_danger_danger_permit_all_and_log flag.
   FILE* log_file_ = nullptr;
+
+  // Handle to the class responsible for proxying and validating connect()
+  // requests.
+  std::unique_ptr<NetworkProxyServer> network_proxy_server_;
+
+  std::thread network_proxy_thread_;
 };
 
 }  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/network_proxy_client.cc b/sandboxed_api/sandbox2/network_proxy_client.cc
deleted file mode 100644
index 5e214e9..0000000
--- a/sandboxed_api/sandbox2/network_proxy_client.cc
+++ /dev/null
@@ -1,217 +0,0 @@
-// Copyright 2019 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-#include "sandboxed_api/sandbox2/network_proxy_client.h"
-
-#include <linux/net.h>
-#include <linux/seccomp.h>
-#include <stdio.h>
-#include <syscall.h>
-#include <ucontext.h>
-
-#include <cerrno>
-#include <iostream>
-
-#include <glog/logging.h>
-#include "absl/memory/memory.h"
-#include "absl/strings/str_cat.h"
-#include "sandboxed_api/sandbox2/util/strerror.h"
-#include "sandboxed_api/util/canonical_errors.h"
-#include "sandboxed_api/util/status.h"
-#include "sandboxed_api/util/status_macros.h"
-
-namespace sandbox2 {
-
-#ifndef SYS_SECCOMP
-constexpr int SYS_SECCOMP = 1;
-#endif
-
-#if defined(__x86_64__)
-constexpr int kRegResult = REG_RAX;
-constexpr int kRegSyscall = REG_RAX;
-constexpr int kRegArg0 = REG_RDI;
-constexpr int kRegArg1 = REG_RSI;
-constexpr int kRegArg2 = REG_RDX;
-#endif
-#if defined(__powerpc64__)
-constexpr int kRegResult = 3;
-constexpr int kRegSyscall = 0;
-constexpr int kRegArg0 = 3;
-constexpr int kRegArg1 = 4;
-constexpr int kRegArg2 = 5;
-#endif
-
-constexpr char NetworkProxyClient::kFDName[];
-
-int NetworkProxyClient::ConnectHandler(int sockfd, const struct sockaddr* addr,
-                                       socklen_t addrlen) {
-  sapi::Status status = Connect(sockfd, addr, addrlen);
-  if (status.ok()) {
-    return 0;
-  }
-  LOG(ERROR) << "ConnectHandler() failed: " << status.message();
-  return -1;
-}
-
-sapi::Status NetworkProxyClient::Connect(int sockfd,
-                                         const struct sockaddr* addr,
-                                         socklen_t addrlen) {
-  absl::MutexLock lock(&mutex_);
-
-  // Check if socket is SOCK_STREAM
-  int type;
-  socklen_t type_size = sizeof(int);
-  int result = getsockopt(sockfd, SOL_SOCKET, SO_TYPE, &type, &type_size);
-  if (result == -1) {
-    return sapi::FailedPreconditionError("Invalid socket FD");
-  }
-  if (type_size != sizeof(int) || type != SOCK_STREAM) {
-    errno = EINVAL;
-    return sapi::InvalidArgumentError(
-        "Invalid socket, only SOCK_STREAM is allowed");
-  }
-
-  // Send sockaddr struct
-  if (!comms_.SendBytes(reinterpret_cast<const uint8_t*>(addr), addrlen)) {
-    errno = EIO;
-    return sapi::InternalError("Sending data to network proxy failed");
-  }
-
-  SAPI_RETURN_IF_ERROR(ReceiveRemoteResult());
-
-  // Receive new socket
-  int s;
-  if (!comms_.RecvFD(&s)) {
-    errno = EIO;
-    return sapi::InternalError("Receiving data from network proxy failed");
-  }
-  if (dup2(s, sockfd) == -1) {
-    close(s);
-    return sapi::InternalError("Processing data from network proxy failed");
-  }
-  return sapi::OkStatus();
-}
-
-sapi::Status NetworkProxyClient::ReceiveRemoteResult() {
-  int result;
-  if (!comms_.RecvInt32(&result)) {
-    errno = EIO;
-    return sapi::InternalError("Receiving data from the network proxy failed");
-  }
-  if (result != 0) {
-    errno = result;
-    return sapi::InternalError(
-        absl::StrCat("Error in network proxy server: ", StrError(errno)));
-  }
-  return sapi::OkStatus();
-}
-
-namespace {
-
-static NetworkProxyHandler* g_network_proxy_handler = nullptr;
-
-void SignalHandler(int nr, siginfo_t* info, void* void_context) {
-  g_network_proxy_handler->ProcessSeccompTrap(nr, info, void_context);
-}
-
-}  // namespace
-
-sapi::Status NetworkProxyHandler::InstallNetworkProxyHandler(
-    NetworkProxyClient* npc) {
-  if (g_network_proxy_handler) {
-    return sapi::AlreadyExistsError(
-        "Network proxy handler is already installed");
-  }
-  g_network_proxy_handler = new NetworkProxyHandler(npc);
-  return sapi::OkStatus();
-}
-
-void NetworkProxyHandler::InvokeOldAct(int nr, siginfo_t* info,
-                                       void* void_context) {
-  if (oldact_.sa_flags & SA_SIGINFO) {
-    if (oldact_.sa_sigaction) {
-      oldact_.sa_sigaction(nr, info, void_context);
-    }
-  } else if (oldact_.sa_handler == SIG_IGN) {
-    return;
-  } else if (oldact_.sa_handler == SIG_DFL) {
-    sigaction(SIGSYS, &oldact_, nullptr);
-    raise(SIGSYS);
-  } else if (oldact_.sa_handler) {
-    oldact_.sa_handler(nr);
-  }
-}  // namespace sandbox2
-
-void NetworkProxyHandler::ProcessSeccompTrap(int nr, siginfo_t* info,
-                                             void* void_context) {
-  ucontext_t* ctx = (ucontext_t*)(void_context);
-  if (info->si_code != SYS_SECCOMP) {
-    InvokeOldAct(nr, info, void_context);
-    return;
-  }
-  if (!ctx) return;
-
-#if defined(__x86_64__)
-  auto* registers = ctx->uc_mcontext.gregs;
-#elif defined(__powerpc64__)
-  auto* registers = ctx->uc_mcontext.gp_regs;
-  using ppc_gpreg_t = std::decay<decltype(registers[0])>::type;
-#endif
-
-  int syscall = registers[kRegSyscall];
-
-  int sockfd;
-  const struct sockaddr* addr;
-  socklen_t addrlen;
-
-  if (syscall == __NR_connect) {
-    sockfd = static_cast<int>(registers[kRegArg0]);
-    addr = reinterpret_cast<const struct sockaddr*>(registers[kRegArg1]);
-    addrlen = static_cast<socklen_t>(registers[kRegArg2]);
-#if defined(__powerpc64__)
-  } else if (syscall == __NR_socketcall &&
-             static_cast<int>(registers[kRegArg0]) == SYS_CONNECT) {
-    ppc_gpreg_t* args = reinterpret_cast<ppc_gpreg_t*>(registers[kRegArg1]);
-
-    sockfd = static_cast<int>(args[0]);
-    addr = reinterpret_cast<const struct sockaddr*>(args[1]);
-    addrlen = static_cast<socklen_t>(args[2]);
-#endif
-  } else {
-    InvokeOldAct(nr, info, void_context);
-    return;
-  }
-
-  sapi::Status result = network_proxy_client_->Connect(sockfd, addr, addrlen);
-  if (result.ok()) {
-    registers[kRegResult] = 0;
-  } else {
-    registers[kRegResult] = -errno;
-  }
-}
-
-void NetworkProxyHandler::InstallSeccompTrap() {
-  sigset_t mask;
-  sigemptyset(&mask);
-  sigaddset(&mask, SIGSYS);
-
-  struct sigaction act = {};
-  act.sa_sigaction = &SignalHandler;
-  act.sa_flags = SA_SIGINFO;
-
-  CHECK_EQ(sigaction(SIGSYS, &act, &oldact_), 0);
-  CHECK_EQ(sigprocmask(SIG_UNBLOCK, &mask, nullptr), 0);
-}
-
-}  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/network_proxy_client.h b/sandboxed_api/sandbox2/network_proxy_client.h
deleted file mode 100644
index 111a1c1..0000000
--- a/sandboxed_api/sandbox2/network_proxy_client.h
+++ /dev/null
@@ -1,75 +0,0 @@
-// Copyright 2019 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-#ifndef SANDBOXED_API_SANDBOX2_NETWORK_PROXY_CLIENT_H_
-#define SANDBOXED_API_SANDBOX2_NETWORK_PROXY_CLIENT_H_
-
-#include <netinet/in.h>
-
-#include "absl/synchronization/mutex.h"
-#include "sandboxed_api/sandbox2/comms.h"
-#include "sandboxed_api/util/status.h"
-
-namespace sandbox2 {
-
-class NetworkProxyClient {
- public:
-  static constexpr char kFDName[] = "sb2_networkproxy";
-
-  explicit NetworkProxyClient(int fd) : comms_(fd) {}
-
-  NetworkProxyClient(const NetworkProxyClient&) = delete;
-  NetworkProxyClient& operator=(const NetworkProxyClient&) = delete;
-
-  // Establishes a new network connection.
-  // Semantic is similar to a regular connect() call.
-  // Arguments are sent to network proxy server, which sends back a connected
-  // socket.
-  sapi::Status Connect(int sockfd, const struct sockaddr* addr,
-                       socklen_t addrlen);
-  // Same as Connect, but with same API as regular connect() call.
-  int ConnectHandler(int sockfd, const struct sockaddr* addr,
-                     socklen_t addrlen);
-
- private:
-  Comms comms_;
-  sapi::Status ReceiveRemoteResult();
-
-  // Needed to make the Proxy thread safe.
-  absl::Mutex mutex_;
-};
-
-class NetworkProxyHandler {
- public:
-  // Installs the handler that redirects connect() syscalls to the trap
-  // function. This function exchange data with NetworkProxyServer that checks
-  // if this connection is allowed and sends the connected socket to us.
-  // In other words, this function just use NetworkProxyClient class.
-  static sapi::Status InstallNetworkProxyHandler(NetworkProxyClient* npc);
-  void ProcessSeccompTrap(int nr, siginfo_t* info, void* void_context);
-
- private:
-  NetworkProxyHandler(NetworkProxyClient* npc) : network_proxy_client_(npc) {
-    InstallSeccompTrap();
-  }
-  void InvokeOldAct(int nr, siginfo_t* info, void* void_context);
-  void InstallSeccompTrap();
-
-  struct sigaction oldact_;
-  NetworkProxyClient* network_proxy_client_;
-};
-
-}  // namespace sandbox2
-
-#endif  // SANDBOXED_API_SANDBOX2_NETWORK_PROXY_CLIENT_H_
diff --git a/sandboxed_api/sandbox2/network_proxy_server.cc b/sandboxed_api/sandbox2/network_proxy_server.cc
deleted file mode 100644
index e0f7552..0000000
--- a/sandboxed_api/sandbox2/network_proxy_server.cc
+++ /dev/null
@@ -1,95 +0,0 @@
-// Copyright 2019 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-#include "sandboxed_api/sandbox2/network_proxy_server.h"
-
-#include <arpa/inet.h>
-#include <netinet/in.h>
-#include <sys/socket.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <syscall.h>
-#include <cerrno>
-#include <cstring>
-
-#include <glog/logging.h>
-#include "absl/memory/memory.h"
-#include "sandboxed_api/sandbox2/util/fileops.h"
-
-namespace sandbox2 {
-
-NetworkProxyServer::NetworkProxyServer(int fd)
-    : comms_{absl::make_unique<Comms>(fd)}, fatal_error_{false} {}
-
-void NetworkProxyServer::ProcessConnectRequest() {
-  std::vector<uint8_t> addr;
-  if (!comms_->RecvBytes(&addr)) {
-    fatal_error_ = true;
-    return;
-  }
-
-  const struct sockaddr_in* saddr =
-      reinterpret_cast<const sockaddr_in*>(addr.data());
-
-  // Only IPv4 TCP and IPv6 TCP are supported.
-  if (!((addr.size() == sizeof(sockaddr_in) && saddr->sin_family == AF_INET) ||
-        (addr.size() == sizeof(sockaddr_in6) &&
-         saddr->sin_family == AF_INET6))) {
-    SendError(EINVAL);
-    return;
-  }
-
-  int new_socket = socket(saddr->sin_family, SOCK_STREAM, 0);
-  if (new_socket < 0) {
-    SendError(errno);
-    return;
-  }
-
-  file_util::fileops::FDCloser new_socket_closer(new_socket);
-
-  int result = connect(
-      new_socket, reinterpret_cast<const sockaddr*>(addr.data()), addr.size());
-
-  if (result == 0) {
-    NotifySuccess();
-    if (!fatal_error_) {
-      if (!comms_->SendFD(new_socket)) {
-        fatal_error_ = true;
-        return;
-      }
-    }
-  }
-}
-
-void NetworkProxyServer::Run() {
-  while (!fatal_error_) {
-    ProcessConnectRequest();
-  }
-  LOG(INFO)
-      << "Clean shutdown or error occurred, shutting down NetworkProxyServer";
-}
-
-void NetworkProxyServer::SendError(int saved_errno) {
-  if (!comms_->SendInt32(saved_errno)) {
-    fatal_error_ = true;
-  }
-}
-
-void NetworkProxyServer::NotifySuccess() {
-  if (!comms_->SendInt32(0)) {
-    fatal_error_ = true;
-  }
-}
-
-}  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/network_proxy_server.h b/sandboxed_api/sandbox2/network_proxy_server.h
deleted file mode 100644
index 55f6c5b..0000000
--- a/sandboxed_api/sandbox2/network_proxy_server.h
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright 2019 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-#ifndef SANDBOXED_API_SANDBOX2_NETWORK_PROXY_SERVER_H_
-#define SANDBOXED_API_SANDBOX2_NETWORK_PROXY_SERVER_H_
-
-#include <memory>
-
-#include "sandboxed_api/sandbox2/comms.h"
-
-namespace sandbox2 {
-
-// This is a proxy server that spawns connected sockets on requests.
-// Then it sends the file descriptor to the requestor. It is used to get around
-// limitations created by network namespaces.
-class NetworkProxyServer {
- public:
-  explicit NetworkProxyServer(int fd);
-
-  NetworkProxyServer(const NetworkProxyServer&) = delete;
-  NetworkProxyServer& operator=(const NetworkProxyServer&) = delete;
-
-  // Starts handling incoming connection requests.
-  void Run();
-
- private:
-  // Notifies the network proxy client about the error and sends its code.
-  void SendError(int saved_errno);
-
-  // Notifies the network proxy client that no error occurred.
-  void NotifySuccess();
-
-  // Serves connection requests from the network proxy client.
-  void ProcessConnectRequest();
-
-  std::unique_ptr<Comms> comms_;
-  bool fatal_error_;
-};
-
-}  // namespace sandbox2
-
-#endif  // SANDBOXED_API_SANDBOX2_NETWORK_PROXY_SERVER_H_
diff --git a/sandboxed_api/sandbox2/policy.h b/sandboxed_api/sandbox2/policy.h
index b507f22..d4a0ca1 100644
--- a/sandboxed_api/sandbox2/policy.h
+++ b/sandboxed_api/sandbox2/policy.h
@@ -31,6 +31,7 @@
 #include "absl/base/macros.h"
 #include "absl/types/optional.h"
 #include "sandboxed_api/sandbox2/namespace.h"
+#include "sandboxed_api/sandbox2/network_proxy/filtering.h"
 #include "sandboxed_api/sandbox2/syscall.h"
 #include "sandboxed_api/sandbox2/violation.pb.h"
 
@@ -104,6 +105,9 @@ class Policy final {
   // Get a policy which would allow the Monitor module to track all syscalls.
   std::vector<sock_filter> GetTrackingPolicy() const;
 
+  // Contains a list of hosts the sandboxee is allowed to connect to.
+  absl::optional<AllowedHosts> allowed_hosts_;
+
   friend class Monitor;
   friend class PolicyBuilder;
   friend class PolicyBuilderPeer;  // For testing
diff --git a/sandboxed_api/sandbox2/policybuilder.cc b/sandboxed_api/sandbox2/policybuilder.cc
index c731e97..99b4b97 100644
--- a/sandboxed_api/sandbox2/policybuilder.cc
+++ b/sandboxed_api/sandbox2/policybuilder.cc
@@ -39,6 +39,7 @@
 #include "sandboxed_api/sandbox2/namespace.h"
 #include "sandboxed_api/sandbox2/util/bpf_helper.h"
 #include "sandboxed_api/sandbox2/util/path.h"
+#include "sandboxed_api/sandbox2/util/strerror.h"
 #include "sandboxed_api/util/canonical_errors.h"
 #include "sandboxed_api/util/status_macros.h"
 
@@ -47,7 +48,7 @@ namespace {
 
 }  // namespace
 
-PolicyBuilder& PolicyBuilder::AllowSyscall(unsigned int num) {
+PolicyBuilder& PolicyBuilder::AllowSyscall(uint32_t num) {
   if (handled_syscalls_.insert(num).second) {
     user_policy_.insert(user_policy_.end(), {SYSCALL(num, ALLOW)});
   }
@@ -68,8 +69,7 @@ PolicyBuilder& PolicyBuilder::AllowSyscalls(SyscallInitializer nums) {
   return *this;
 }
 
-PolicyBuilder& PolicyBuilder::BlockSyscallWithErrno(unsigned int num,
-                                                    int error) {
+PolicyBuilder& PolicyBuilder::BlockSyscallWithErrno(uint32_t num, int error) {
   if (handled_syscalls_.insert(num).second) {
     user_policy_.insert(user_policy_.end(), {SYSCALL(num, ERRNO(error))});
   }
@@ -545,17 +545,17 @@ PolicyBuilder& PolicyBuilder::AllowDynamicStartup() {
   });
 }
 
-PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(unsigned int num,
+PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(uint32_t num,
                                                  BpfInitializer policy) {
   return AddPolicyOnSyscalls({num}, policy);
 }
 
 PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(
-    unsigned int num, const std::vector<sock_filter>& policy) {
+    uint32_t num, const std::vector<sock_filter>& policy) {
   return AddPolicyOnSyscalls({num}, policy);
 }
 
-PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(unsigned int num, BpfFunc f) {
+PolicyBuilder& PolicyBuilder::AddPolicyOnSyscall(uint32_t num, BpfFunc f) {
   return AddPolicyOnSyscalls({num}, f);
 }
 
@@ -700,6 +700,7 @@ sapi::StatusOr<std::unique_ptr<Policy>> PolicyBuilder::TryBuild() {
 
   StoreDescription(pb_description.get());
   output->policy_builder_description_ = std::move(pb_description);
+  output->allowed_hosts_ = std::move(allowed_hosts_);
   already_built_ = true;
   return std::move(output);
 }
@@ -848,6 +849,15 @@ PolicyBuilder& PolicyBuilder::CollectStacktracesOnKill(bool enable) {
 }
 
 PolicyBuilder& PolicyBuilder::AddNetworkProxyPolicy() {
+  if (allowed_hosts_) {
+    SetError(sapi::FailedPreconditionError(
+        "AddNetworkProxyPolicy or AddNetworkProxyHandlerPolicy can be called "
+        "at most once"));
+    return *this;
+  }
+
+  allowed_hosts_ = AllowedHosts();
+
   AllowFutexOp(FUTEX_WAKE);
   AllowFutexOp(FUTEX_WAIT);
   AllowFutexOp(FUTEX_WAIT_BITSET);
@@ -920,4 +930,36 @@ void PolicyBuilder::StoreDescription(PolicyBuilderDescription* pb_description) {
   }
 }
 
+PolicyBuilder& PolicyBuilder::AllowIPv4(const std::string& ip_and_mask,
+                                        uint32_t port) {
+  if (!allowed_hosts_) {
+    SetError(sapi::FailedPreconditionError(
+        "AddNetworkProxyPolicy or AddNetworkProxyHandlerPolicy must be called "
+        "before adding IP rules"));
+    return *this;
+  }
+
+  sapi::Status status = allowed_hosts_->AllowIPv4(ip_and_mask, port);
+  if (!status.ok()) {
+    SetError(status);
+  }
+  return *this;
+}
+
+PolicyBuilder& PolicyBuilder::AllowIPv6(const std::string& ip_and_mask,
+                                        uint32_t port) {
+  if (!allowed_hosts_) {
+    SetError(sapi::FailedPreconditionError(
+        "AddNetworkProxyPolicy or AddNetworkProxyHandlerPolicy must be called "
+        "before adding IP rules"));
+    return *this;
+  }
+
+  sapi::Status status = allowed_hosts_->AllowIPv6(ip_and_mask, port);
+  if (!status.ok()) {
+    SetError(status);
+  }
+  return *this;
+}
+
 }  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/policybuilder.h b/sandboxed_api/sandbox2/policybuilder.h
index b9d48db..c4997a7 100644
--- a/sandboxed_api/sandbox2/policybuilder.h
+++ b/sandboxed_api/sandbox2/policybuilder.h
@@ -31,6 +31,7 @@
 #include "absl/memory/memory.h"
 #include "absl/strings/string_view.h"
 #include "sandboxed_api/sandbox2/mounts.h"
+#include "sandboxed_api/sandbox2/network_proxy/filtering.h"
 #include "sandboxed_api/sandbox2/policy.h"
 #include "sandboxed_api/util/statusor.h"
 
@@ -501,6 +502,10 @@ class PolicyBuilder final {
   // Not recommended
   PolicyBuilder& SetRootWritable();
 
+  // Allows connections to this IP.
+  PolicyBuilder& AllowIPv4(const std::string& ip_and_mask, uint32_t port = 0);
+  PolicyBuilder& AllowIPv6(const std::string& ip_and_mask, uint32_t port = 0);
+
  private:
   friend class PolicyBuilderPeer;  // For testing
   friend class StackTracePeer;
@@ -542,6 +547,9 @@ class PolicyBuilder final {
   // This function returns a PolicyBuilder so that we can use it in the status
   // macros
   PolicyBuilder& SetError(const sapi::Status& status);
+
+  // Contains list of allowed hosts.
+  absl::optional<AllowedHosts> allowed_hosts_;
 };
 
 }  // namespace sandbox2
diff --git a/sandboxed_api/sandbox2/result.cc b/sandboxed_api/sandbox2/result.cc
index 1fa194f..a83e457 100644
--- a/sandboxed_api/sandbox2/result.cc
+++ b/sandboxed_api/sandbox2/result.cc
@@ -79,6 +79,10 @@ std::string Result::ToString() const {
                             Syscall(GetSyscallArch(), reason_code()).GetName(),
                             "] Stack: ", GetStackTrace());
       break;
+    case sandbox2::Result::NETWORK_VIOLATION:
+      result = absl::StrCat("NETWORK VIOLATION - Violating network policy: ",
+                            network_violation_);
+      break;
     case sandbox2::Result::SIGNALED:
       result = absl::StrCat("Process terminated with a SIGNAL - Signal: ",
                             util::GetSignalName(reason_code()),
@@ -129,6 +133,8 @@ std::string Result::StatusEnumToString(StatusEnum value) {
       return "SETUP_ERROR";
     case sandbox2::Result::VIOLATION:
       return "VIOLATION";
+    case sandbox2::Result::NETWORK_VIOLATION:
+      return "NETWORK_VIOLATION";
     case sandbox2::Result::SIGNALED:
       return "SIGNALED";
     case sandbox2::Result::TIMEOUT:
diff --git a/sandboxed_api/sandbox2/result.h b/sandboxed_api/sandbox2/result.h
index 77cb043..cbda608 100644
--- a/sandboxed_api/sandbox2/result.h
+++ b/sandboxed_api/sandbox2/result.h
@@ -45,6 +45,8 @@ class Result {
     SETUP_ERROR,
     // Syscall violation
     VIOLATION,
+    // Network policy violation
+    NETWORK_VIOLATION,
     // Process terminated with a signal
     SIGNALED,
     // Process terminated with a timeout
@@ -119,6 +121,10 @@ class Result {
     syscall_ = std::move(syscall);
   }
 
+  void SetNetworkViolation(std::string network_violation) {
+    network_violation_ = std::move(network_violation);
+  }
+
   StatusEnum final_status() const { return final_status_; }
   uintptr_t reason_code() const { return reason_code_; }
 
@@ -137,6 +143,8 @@ class Result {
 
   const std::string& GetProgName() const { return prog_name_; }
 
+  const std::string& GetNetworkViolation() const { return network_violation_; }
+
   void SetProgName(const std::string& name) { prog_name_ = name; }
 
   const std::string& GetProcMaps() const { return proc_maps_; }
@@ -179,6 +187,8 @@ class Result {
   std::string prog_name_;
   // /proc/pid/maps of the main process.
   std::string proc_maps_;
+  // IP and port if network violation occurred
+  std::string network_violation_;
   // Final resource usage as defined in <sys/resource.h> (man getrusage), for
   // the Monitor thread.
   rusage rusage_monitor_;