diff --git a/include/protocol.h b/include/protocol.h
index 461ed55..cb7e191 100644
--- a/include/protocol.h
+++ b/include/protocol.h
@@ -10,9 +10,11 @@
 #define OWD_DATA_LEN(HDR) (offsetof(__typeof__(HDR), _data_end))
 
 enum owd_msg_type {
-  OWD_MSG_ERR,
-  OWD_MSG_SYNC_REQUEST,
-  OWD_MSG_SYNC_RESPONSE,
+  OWD_MSG_ERR           = 0,
+  OWD_MSG_PING          = 1,
+  OWD_MSG_PONG          = 2,
+  OWD_MSG_SYNC_REQUEST  = 3,
+  OWD_MSG_SYNC_RESPONSE = 4,
 };
 
 enum owd_error_code {
@@ -30,6 +32,7 @@ struct owdhdr {
   uint8_t version;
   uint8_t msg_type;
   uint16_t length;
+  uint32_t tid;
 };
 
 struct owd_msg_err {
@@ -44,9 +47,25 @@ struct owd_msg_sync_response {
   OWD_DECL_DATA_END;
 };
 
-static inline void owd_hdr_populate(struct owdhdr *hdr, uint8_t msg_type, uint16_t length) {
+static inline void owd_hdr_populate(
+  struct owdhdr *hdr,
+  uint8_t msg_type,
+  uint16_t length,
+  uint32_t tid)
+{
   hdr->magic = htonl(OWD_MAGIC);
   hdr->version = OWD_VERSION;
   hdr->msg_type = msg_type;
   hdr->length = htons(length);
+  hdr->tid = htonl(tid);
+}
+
+static inline int owd_hdr_validate(struct owdhdr *hdr, ssize_t len) {
+  if (len < sizeof(struct owdhdr))
+    return 1;
+  if (hdr->magic != ntohl(OWD_MAGIC))
+    return 1;
+  if (hdr->version != OWD_VERSION)
+    return 1;
+  return 0;
 }
diff --git a/src/server.c b/src/server.c
index b901fff..018528c 100644
--- a/src/server.c
+++ b/src/server.c
@@ -8,6 +8,7 @@
 #include <netinet/in.h>
 
 #include "server.h"
+#include "io.h"
 #include "util.h"
 #include "protocol.h"
 
@@ -19,16 +20,13 @@ struct rx_info {
   const void *name;
   socklen_t namelen;
   struct timeval tv;
+  uint32_t tid;
   uint8_t tv_set : 1;
 };
 
-static int setsockopt_int(int fd, int level, int option, int val) {
-  return setsockopt(fd, level, option, &val, sizeof(val));
-}
-
 static int server_init(const struct server_conf *conf, struct server_ctx *ctx) {
   struct sockaddr_in6 server_addr = { 0 };
-  int sock_fd;
+  FD_SCOPED(sock_fd);
 
   server_addr.sin6_family = AF_INET6;
   server_addr.sin6_addr = in6addr_any;
@@ -39,17 +37,15 @@ static int server_init(const struct server_conf *conf, struct server_ctx *ctx) {
 
   if (setsockopt_int(sock_fd, SOL_SOCKET, SO_REUSEADDR, 1))
     FAIL("failed to set SO_REUSEADDR: %s", strerror(errno));
-
   if (setsockopt_int(sock_fd, SOL_SOCKET, SO_TIMESTAMP, 1))
     FAIL("failed to set SO_TIMESTAMP: %s", strerror(errno));
-
   if (setsockopt_int(sock_fd, IPPROTO_IPV6, IPV6_V6ONLY, 0))
     FAIL("failed to set IPV6_V6ONLY: %s", strerror(errno));
 
   if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)))
     FAIL("failed to bind: %s", strerror(errno));
 
-  ctx->fd = sock_fd;
+  ctx->fd = FD_RELEASE(&sock_fd);
   return 0;
 }
 
@@ -79,12 +75,21 @@ static void send_error_msg(
 {
   struct owd_msg_err msg;
 
-  owd_hdr_populate(&msg.hdr, OWD_MSG_ERR, OWD_DATA_LEN(msg));
+  owd_hdr_populate(&msg.hdr, OWD_MSG_ERR, OWD_DATA_LEN(msg), rx->tid);
   msg.err = (uint8_t)err;
   if (send_to_client(ctx, rx, &msg, OWD_DATA_LEN(msg)))
     LOG_ERR("failed to send error message");
 }
 
+static int handle_ping(struct server_ctx *ctx, const struct rx_info *rx) {
+  struct owdhdr hdr;
+
+  owd_hdr_populate(&hdr, OWD_MSG_PONG, sizeof(hdr), rx->tid);
+  if (send_to_client(ctx, rx, &hdr, sizeof(hdr)))
+    FAIL("failed to send pong");
+  return 0;
+}
+
 static int handle_sync_request(struct server_ctx *ctx, const struct rx_info *rx) {
   if (!rx->tv_set)
     FAIL("no rx timestamp available");
@@ -99,6 +104,7 @@ static int handle_msg(struct server_ctx *ctx, char *buf, ssize_t buf_len, struct
   struct rx_info rx;
 
   rx.tv_set = false;
+  rx.tid = 0;
   rx.name = msg_hdr->msg_name;
   rx.namelen = msg_hdr->msg_namelen;
 
@@ -116,18 +122,18 @@ static int handle_msg(struct server_ctx *ctx, char *buf, ssize_t buf_len, struct
     }
   }
 
-  if (rx.tv_set) {
-    printf("  tv_sec=%lld tv_usec=%lld\n", (long long)rx.tv.tv_sec, (long long)rx.tv.tv_usec);
-  }
-
-  if (buf_len < sizeof(struct owdhdr)) {
+  hdr = (struct owdhdr *)buf;
+  if (owd_hdr_validate(hdr, buf_len)) {
     send_error_msg(ctx, &rx, OWD_ERR_BAD_HEADER);
-    FAIL("invalid packet: too short");
+    FAIL("invalid packet: bad header");
   }
 
-  hdr = (struct owdhdr *)buf;
+  rx.tid = ntohl(hdr->tid);
 
   switch (hdr->msg_type) {
+    case OWD_MSG_PING:
+      return handle_ping(ctx, &rx);
+    
     case OWD_MSG_SYNC_REQUEST:
       return handle_sync_request(ctx, &rx);
 
@@ -157,8 +163,6 @@ static int server_loop(struct server_ctx *ctx) {
     msg_hdr.msg_control = ctrl_buf;
     msg_hdr.msg_controllen = sizeof(ctrl_buf);
 
-    printf("namelen_before=%zu\n", (size_t)msg_hdr.msg_namelen);
-
     if ((recv_res = recvmsg(ctx->fd, &msg_hdr, 0)) < 0) {
       if ((errno == EINTR) || (errno == EAGAIN) || (errno == EWOULDBLOCK))
         continue;
@@ -167,8 +171,6 @@ static int server_loop(struct server_ctx *ctx) {
       continue;
     }
 
-    printf("namelen_after=%zu\n", (size_t)msg_hdr.msg_namelen);
-
     handle_msg(ctx, msg_buf, recv_res, &msg_hdr);
   }
 }