diff --git a/lab3/demos/Makefile b/lab3/demos/Makefile
new file mode 100644
index 0000000..a2f0f6c
--- /dev/null
+++ b/lab3/demos/Makefile
@@ -0,0 +1,10 @@
+all: server client
+
+server: server.c
+	gcc -Wall -Wextra -Werror -D_POSIX_C_SOURCE=201112L -o server server.c
+
+client: client.c
+	gcc -Wall -Wextra -Werror -D_POSIX_C_SOURCE=201112L -o client client.c
+
+clean:
+	rm -f server client
diff --git a/lab3/demos/client.c b/lab3/demos/client.c
new file mode 100644
index 0000000..5d5c9c9
--- /dev/null
+++ b/lab3/demos/client.c
@@ -0,0 +1,90 @@
+#include <netdb.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define PORT "1025"
+#define HOST "localhost"
+#define SOURCE_PORT "1026"
+
+int create_client_sock(char* port, char* host, char* source_port) {
+    struct addrinfo hints = {
+        .ai_family = AF_INET6,
+        .ai_socktype = SOCK_STREAM,
+        .ai_flags = AI_V4MAPPED,
+    };
+
+    struct addrinfo* res;
+    int err = getaddrinfo(host, port, &hints, &res);
+    if (err != 0) {
+        fprintf(stderr, "%s\n", gai_strerror(err));
+        _exit(1);
+    }
+
+    struct addrinfo *self;
+    err = getaddrinfo(NULL, source_port, &hints, &self);
+    if (err != 0) {
+        fprintf(stderr, "%s\n", gai_strerror(err));
+        _exit(1);
+    }
+
+    int sfd;
+    struct addrinfo* cur = res;
+
+    for (; cur != NULL; cur = cur->ai_next) {
+        // socket
+        sfd = socket(cur->ai_family, cur->ai_socktype, cur->ai_protocol);
+        if (sfd == -1) {
+            perror("socket");
+            continue;
+        }
+
+        int val = 1;
+        err = setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
+        if (err == -1) {
+            perror("setsockopt");
+            close(sfd);
+            continue;
+        }
+
+        // Bind
+        err = bind(sfd, self->ai_addr, self->ai_addrlen);
+        if (err == -1) {
+            perror("bind");
+            close(sfd);
+            continue;
+        }
+
+        // Connect
+        err = connect(sfd, res->ai_addr, res->ai_addrlen);
+        if (err == -1) {
+            perror("connect");
+            close(sfd);
+            continue;
+        }
+
+        break;
+    }
+
+    freeaddrinfo(res);
+    freeaddrinfo(self);
+
+    if (cur == NULL) {
+        fprintf(stderr, "failed to connect to the server\n");
+        _exit(1);
+    }
+
+    return sfd;
+}
+
+int main() {
+    int cfd = create_client_sock(PORT, HOST, SOURCE_PORT);
+
+    char* msg = "This is a test message!\n";
+    write(cfd, msg, strlen(msg));
+    printf("message send: \"%s\"\n", msg);
+
+    close(cfd);
+}
diff --git a/lab3/demos/server.c b/lab3/demos/server.c
new file mode 100644
index 0000000..d9cc649
--- /dev/null
+++ b/lab3/demos/server.c
@@ -0,0 +1,103 @@
+#include <netdb.h>
+#include <stdio.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define PORT "1025"
+#define BACKLOG 4
+#define BUF_SIZE 20
+
+int create_server_sock(char* port) {
+    struct addrinfo hints = {
+        .ai_family = AF_INET6,
+        .ai_socktype = SOCK_STREAM,
+        .ai_flags = AI_PASSIVE || AI_V4MAPPED
+    };
+
+    struct addrinfo *res;
+    int err = getaddrinfo(NULL, port, &hints, &res);
+    if (err != 0) {
+        fprintf(stderr, "gai_err %s\n", gai_strerror(err));
+        _exit(1);
+    }
+
+    int sfd;
+    struct addrinfo* cur = res;
+
+    for (; cur != NULL; cur = cur->ai_next) {
+        // create socket
+        sfd = socket(cur->ai_family, cur->ai_socktype, cur->ai_protocol);
+        if (sfd == -1) {
+            perror("socket");
+            continue;
+        }
+
+        int val = 1;
+        err = setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
+        if (err == -1) {
+            perror("setsockopt");
+            close(sfd);
+            continue;
+        }
+
+        // Bind
+        err = bind(sfd, cur->ai_addr, cur->ai_addrlen);
+        if (err == -1) {
+            perror("bind");
+            close(sfd);
+            continue;
+        }
+
+        // Listen
+        err = listen(sfd, BACKLOG);
+        if (err == -1) {
+            perror("listen");
+            close(sfd);
+            continue;
+        }
+
+        break;
+    }
+
+    freeaddrinfo(res);
+
+    if (cur == NULL) {
+        fprintf(stderr, "failed to create socket\n");
+        close(sfd);
+        _exit(1);
+    }
+
+    return sfd;
+}
+
+int main() {
+    int sfd = create_server_sock(PORT);
+
+    struct sockaddr_storage client_addr;
+    socklen_t client_addr_len = sizeof(client_addr);
+
+    int cfd = accept(sfd, (struct sockaddr*) &client_addr, &client_addr_len);
+    if (cfd == -1) {
+        perror("accept");
+        _exit(1);
+    }
+
+    int n;
+    uint8_t buf[BUF_SIZE];
+
+    while ((n = read(cfd, buf, BUF_SIZE)) > 0) {
+        if (n == -1) {
+            perror("read");
+            _exit(1);
+        }
+        if (write(STDOUT_FILENO, buf, n) == -1) {
+            perror("read");
+            _exit(1);
+        }
+    }
+
+    close(sfd);
+
+    return 0;
+}