diff --git a/src/ICS02Client.sol b/src/ICS02Client.sol
index 51649ce..bb83be5 100644
--- a/src/ICS02Client.sol
+++ b/src/ICS02Client.sol
@@ -36,14 +36,27 @@ contract ICS02Client is IICS02Client, IICS02ClientErrors {
         return clients[clientId];
     }
 
-    function addClient(string calldata clientType, CounterpartyInfo calldata counterpartyInfo, address client) external returns (string memory) {
+    function addClient(
+        string calldata clientType,
+        CounterpartyInfo calldata counterpartyInfo,
+        address client
+    )
+        external
+        returns (string memory)
+    {
         string memory clientId = getNextClientId(clientType);
         clients[clientId] = ILightClient(client);
         counterpartyInfos[clientId] = counterpartyInfo;
         return clientId;
     }
 
-    function updateClient(string calldata clientId, bytes calldata updateMsg) external returns (ILightClient.UpdateResult) {
+    function updateClient(
+        string calldata clientId,
+        bytes calldata updateMsg
+    )
+        external
+        returns (ILightClient.UpdateResult)
+    {
         return clients[clientId].updateClient(updateMsg);
     }
 
diff --git a/src/ICS26Router.sol b/src/ICS26Router.sol
index 4240727..0b4e2d5 100644
--- a/src/ICS26Router.sol
+++ b/src/ICS26Router.sol
@@ -11,10 +11,12 @@ import { Strings } from "@openzeppelin/contracts/utils/Strings.sol";
 import { IBCIdentifiers } from "./utils/IBCIdentifiers.sol";
 import { IIBCAppCallbacks } from "./msgs/IIBCAppCallbacks.sol";
 import { ICS24Host } from "./utils/ICS24Host.sol";
+import { ILightClientMsgs } from "./msgs/ILightClientMsgs.sol";
+import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
 
 /// @title IBC Eureka Router
 /// @notice ICS26Router is the router for the IBC Eureka protocol
-contract ICS26Router is IICS26Router, IBCStore, Ownable, IICS26RouterErrors {
+contract ICS26Router is IICS26Router, IBCStore, Ownable, IICS26RouterErrors, ReentrancyGuard {
     mapping(string => IIBCApp) private apps;
     IICS02Client private ics02Client;
 
@@ -55,14 +57,12 @@ contract ICS26Router is IICS26Router, IBCStore, Ownable, IICS26RouterErrors {
     /// @notice Sends a packet
     /// @param msg_ The message for sending packets
     /// @return The sequence number of the packet
-    function sendPacket(MsgSendPacket calldata msg_) external returns (uint32) {
-        IIBCApp app = apps[msg_.sourcePort];
-
+    function sendPacket(MsgSendPacket calldata msg_) external nonReentrant returns (uint32) {
         string memory counterpartyId = ics02Client.getCounterparty(msg_.sourcePort).clientId;
 
         // TODO: validate all identifiers
         if (msg_.timeoutTimestamp <= block.timestamp) {
-            revert IBCInvalidTimeoutTimestamp(msg_.timeoutTimestamp);
+            revert IBCInvalidTimeoutTimestamp(msg_.timeoutTimestamp, block.timestamp);
         }
 
         uint32 sequence = IBCStore.nextSequenceSend(msg_.sourcePort, msg_.sourceChannel);
@@ -81,7 +81,7 @@ contract ICS26Router is IICS26Router, IBCStore, Ownable, IICS26RouterErrors {
         IIBCAppCallbacks.OnSendPacketCallback memory sendPacketCallback =
             IIBCAppCallbacks.OnSendPacketCallback({ packet: packet, sender: msg.sender });
 
-        app.onSendPacket(sendPacketCallback); // TODO: do not allow reentrancy
+        apps[msg_.sourcePort].onSendPacket(sendPacketCallback);
 
         IBCStore.commitPacket(packet);
 
@@ -91,7 +91,7 @@ contract ICS26Router is IICS26Router, IBCStore, Ownable, IICS26RouterErrors {
 
     /// @notice Receives a packet
     /// @param msg_ The message for receiving packets
-    function recvPacket(MsgRecvPacket calldata msg_) external {
+    function recvPacket(MsgRecvPacket calldata msg_) external nonReentrant {
         // TODO: implement
         IIBCApp app = apps[msg_.packet.destPort];
 
@@ -101,24 +101,52 @@ contract ICS26Router is IICS26Router, IBCStore, Ownable, IICS26RouterErrors {
         }
 
         bytes memory commitmentPath = ICS24Host.packetCommitmentPathCalldata(
-            msg_.packet.sourcePort,
-            msg_.packet.sourceChannel,
-            msg_.packet.sequence
+            msg_.packet.sourcePort, msg_.packet.sourceChannel, msg_.packet.sequence
         );
         bytes32 commitmentBz = ICS24Host.packetCommitmentBytes32(msg_.packet);
+
+        ILightClientMsgs.MsgMembership memory membershipMsg = ILightClientMsgs.MsgMembership({
+            proof: msg_.proofCommitment,
+            proofHeight: msg_.proofHeight,
+            kvPair: ILightClientMsgs.KVPair({ path: commitmentPath, value: abi.encodePacked(commitmentBz) })
+        });
+
+        uint32 proofTimestamp = ics02Client.getClient(msg_.packet.destChannel).verifyMembership(membershipMsg);
+        if (msg_.packet.timeoutTimestamp <= proofTimestamp) {
+            revert IBCInvalidTimeoutTimestamp(proofTimestamp, msg_.packet.timeoutTimestamp);
+        }
+        if (msg_.packet.timeoutTimestamp <= block.timestamp) {
+            revert IBCInvalidTimeoutTimestamp(msg_.packet.timeoutTimestamp, block.timestamp);
+        }
+
+        bytes memory ack =
+            app.onRecvPacket(IIBCAppCallbacks.OnRecvPacketCallback({ packet: msg_.packet, relayer: msg.sender }));
+        if (ack.length == 0) {
+            revert IBCAsyncAcknowledgementNotSupported();
+        }
+
+        writeAcknowledgement(msg_.packet, ack);
+
+        emit RecvPacket(msg_.packet);
     }
 
     /// @notice Acknowledges a packet
     /// @param msg_ The message for acknowledging packets
-    function ackPacket(MsgAckPacket calldata msg_) external {
+    function ackPacket(MsgAckPacket calldata msg_) external nonReentrant {
         // TODO: implement
         // IIBCApp app = IIBCApp(apps[msg.packet.sourcePort]);
     }
 
     /// @notice Timeouts a packet
     /// @param msg_ The message for timing out packets
-    function timeoutPacket(MsgTimeoutPacket calldata msg_) external {
+    function timeoutPacket(MsgTimeoutPacket calldata msg_) external nonReentrant {
         // TODO: implement
         // IIBCApp app = IIBCApp(apps[msg.packet.sourcePort]);
     }
+
+    /// @notice Writes a packet acknowledgement and emits an event
+    function writeAcknowledgement(Packet calldata packet, bytes memory ack) private {
+        IBCStore.commitPacketAcknowledgement(packet, ack);
+        emit WriteAcknowledgement(packet, ack);
+    }
 }
diff --git a/src/errors/IICS26RouterErrors.sol b/src/errors/IICS26RouterErrors.sol
index b4b1658..8881565 100644
--- a/src/errors/IICS26RouterErrors.sol
+++ b/src/errors/IICS26RouterErrors.sol
@@ -9,9 +9,11 @@ interface IICS26RouterErrors {
     error IBCInvalidPortIdentifier(string portId);
 
     /// @param timeoutTimestamp timeout timestamp in seconds
-    error IBCInvalidTimeoutTimestamp(uint32 timeoutTimestamp);
+    error IBCInvalidTimeoutTimestamp(uint256 timeoutTimestamp, uint256 comparedTimestamp);
 
     /// @param expected expected counterparty identifier
     /// @param actual actual counterparty identifier
     error IBCInvalidCounterparty(string expected, string actual);
+
+    error IBCAsyncAcknowledgementNotSupported();
 }
diff --git a/src/interfaces/IICS02Client.sol b/src/interfaces/IICS02Client.sol
index d099c33..1e921a8 100644
--- a/src/interfaces/IICS02Client.sol
+++ b/src/interfaces/IICS02Client.sol
@@ -22,7 +22,13 @@ interface IICS02Client is IICS02ClientMsgs {
     /// @param counterpartyInfo The counterparty client information
     /// @param client The address of the client contract
     /// @return The client identifier
-    function addClient(string calldata clientType, CounterpartyInfo calldata counterpartyInfo, address client) external returns (string memory);
+    function addClient(
+        string calldata clientType,
+        CounterpartyInfo calldata counterpartyInfo,
+        address client
+    )
+        external
+        returns (string memory);
 
     /// @notice Updates the client given the client identifier.
     /// @param clientId The client identifier
diff --git a/test/IbcIdentifiers.t.sol b/test/IbcIdentifiers.t.sol
index 442fd53..cce3637 100644
--- a/test/IbcIdentifiers.t.sol
+++ b/test/IbcIdentifiers.t.sol
@@ -15,68 +15,29 @@ contract IBCIdentifiersTest is Test {
         // The following test cases are based on the test cases of ibc-go:
         // https://github.com/cosmos/ibc-go/blob/e443a88e0f2c84c131c5a1de47945a5733ff9c91/modules/core/24-host/validate_test.go#L57
         ValidatePortIdentifierTestCase[] memory testCases = new ValidatePortIdentifierTestCase[](12);
-        testCases[0] = ValidatePortIdentifierTestCase({
-            m: "valid lowercase",
-            id: "transfer",
-            expPass: true
-        });
-        testCases[1] = ValidatePortIdentifierTestCase({
-            m: "valid id special chars",
-            id: "._+-#[]<>._+-#[]<>",
-            expPass: true
-        });
+        testCases[0] = ValidatePortIdentifierTestCase({ m: "valid lowercase", id: "transfer", expPass: true });
+        testCases[1] =
+            ValidatePortIdentifierTestCase({ m: "valid id special chars", id: "._+-#[]<>._+-#[]<>", expPass: true });
         testCases[2] = ValidatePortIdentifierTestCase({
             m: "valid id lower and special chars",
             id: "lower._+-#[]<>",
             expPass: true
         });
-        testCases[3] = ValidatePortIdentifierTestCase({
-            m: "numeric id",
-            id: "1234567890",
-            expPass: true
-        });
-        testCases[4] = ValidatePortIdentifierTestCase({
-            m: "uppercase id",
-            id: "NOTLOWERCASE",
-            expPass: true
-        });
-        testCases[5] = ValidatePortIdentifierTestCase({
-            m: "numeric id",
-            id: "1234567890",
-            expPass: true
-        });
-        testCases[6] = ValidatePortIdentifierTestCase({
-            m: "blank id",
-            id: "               ",
-            expPass: false
-        });
-        testCases[7] = ValidatePortIdentifierTestCase({
-            m: "id length out of range",
-            id: "1",
-            expPass: false
-        });
+        testCases[3] = ValidatePortIdentifierTestCase({ m: "numeric id", id: "1234567890", expPass: true });
+        testCases[4] = ValidatePortIdentifierTestCase({ m: "uppercase id", id: "NOTLOWERCASE", expPass: true });
+        testCases[5] = ValidatePortIdentifierTestCase({ m: "numeric id", id: "1234567890", expPass: true });
+        testCases[6] = ValidatePortIdentifierTestCase({ m: "blank id", id: "               ", expPass: false });
+        testCases[7] = ValidatePortIdentifierTestCase({ m: "id length out of range", id: "1", expPass: false });
         testCases[8] = ValidatePortIdentifierTestCase({
             m: "id is too long",
             id: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis eros neque, ultricies vel ligula ac, convallis porttitor elit. Maecenas tincidunt turpis elit, vel faucibus nisl pellentesque sodales",
             expPass: false
         });
-        testCases[9] = ValidatePortIdentifierTestCase({
-            m: "path-like id",
-            id: "lower/case/id",
-            expPass: false
-        });
-        testCases[10] = ValidatePortIdentifierTestCase({
-            m: "invalid id",
-            id: "(clientid)",
-            expPass: false
-        });
-        testCases[11] = ValidatePortIdentifierTestCase({
-            m: "empty string",
-            id: "",
-            expPass: false
-        });
+        testCases[9] = ValidatePortIdentifierTestCase({ m: "path-like id", id: "lower/case/id", expPass: false });
+        testCases[10] = ValidatePortIdentifierTestCase({ m: "invalid id", id: "(clientid)", expPass: false });
+        testCases[11] = ValidatePortIdentifierTestCase({ m: "empty string", id: "", expPass: false });
 
-        for (uint i = 0; i < testCases.length; i++) {
+        for (uint256 i = 0; i < testCases.length; i++) {
             ValidatePortIdentifierTestCase memory tc = testCases[i];
             bool res = IBCIdentifiers.validatePortIdentifier(bytes(tc.id));
             if (tc.expPass) {