diff --git a/Protocol/src/include/protocol/protocol.hxx b/Protocol/src/include/protocol/protocol.hxx
index 1494ae3..606a7c6 100644
--- a/Protocol/src/include/protocol/protocol.hxx
+++ b/Protocol/src/include/protocol/protocol.hxx
@@ -22,4 +22,13 @@ struct SignedMessage {
       bool valid(unsigned char pub_key[crypto_sign_PUBLICKEYBYTES]);
 };
 
+struct StunReplay {
+      uint32_t addr; // ipv4 only support!
+      uint16_t port;
+      bool is_behind_symmetric_nat = false;
+
+      StunReplay(std::string ip, uint16_t port);
+      StunReplay(uint32_t ip, uint16_t port);
+};
+
 } // namespace Protocol
diff --git a/Protocol/src/protocol.cxx b/Protocol/src/protocol.cxx
index 70572c2..61e99f3 100644
--- a/Protocol/src/protocol.cxx
+++ b/Protocol/src/protocol.cxx
@@ -1,6 +1,7 @@
 #include <chrono>
 #include <cstring>
 #include <protocol/protocol.hxx>
+#include <ranges>
 #include <sodium.h>
 
 namespace Protocol {
@@ -57,4 +58,29 @@ bool SignedMessage::valid(unsigned char pub_key[crypto_sign_PUBLICKEYBYTES]) {
       return true;
 }
 
+StunReplay::StunReplay(std::string ip, uint16_t port) : port(port) {
+      auto parts =
+          ip | std::views::split('.') | std::views::transform([](auto &&range) {
+                return std::string_view(range.cbegin(), range.cend());
+          });
+      if (std::ranges::distance(parts) != 4) {
+            goto invalid_addr;
+      }
+
+      for (auto part : parts) {
+            auto val = std::atoi(part.data());
+            if (val > 255 || val < 1) {
+                  goto invalid_addr;
+            }
+            addr = (addr << 8) | static_cast<uint32_t>(val);
+      }
+
+      goto end;
+invalid_addr:
+      throw std::runtime_error("Invalid ipv4 string");
+end:
+}
+
+StunReplay::StunReplay(uint32_t ip, uint16_t port) : addr(ip), port(port) {}
+
 } // namespace Protocol
diff --git a/Protocol/tests/test_protocol.cxx b/Protocol/tests/test_protocol.cxx
index c5454fd..6368104 100644
--- a/Protocol/tests/test_protocol.cxx
+++ b/Protocol/tests/test_protocol.cxx
@@ -3,7 +3,24 @@
 #include <protocol/protocol.hxx>
 #include <sodium.h>
 
-TEST_CASE("SignedMessage", "[protocol]") {
+TEST_CASE("Protocol::StunReplay", "[protocol]") {
+      SECTION("str to ipv4") {
+            auto replay = Protocol::StunReplay("1.1.255.255", 1337);
+            REQUIRE(replay.addr == 16908287);
+      }
+      SECTION("invalid ipv4 str (range)") {
+            REQUIRE_THROWS_AS(Protocol::StunReplay("1.1.255.256", 1337),
+                              std::runtime_error);
+            REQUIRE_THROWS_AS(Protocol::StunReplay("0.1.255.255", 1337),
+                              std::runtime_error);
+      }
+      SECTION("invalid ipv4 str (len)") {
+            REQUIRE_THROWS_AS(Protocol::StunReplay("1.1.1", 1337),
+                              std::runtime_error);
+      }
+}
+
+TEST_CASE("Protocol::SignedMessage", "[protocol]") {
       REQUIRE(sodium_init() >= 0);
 
       unsigned char pub_key[crypto_sign_PUBLICKEYBYTES];