Add week 7 materials

2026-10-21 23:03:28 +03:00
parent 4bb38fb0a8
commit a987b82834
22 changed files with 1265 additions and 0 deletions
@@ -0,0 +1,31 @@
+"""Obtain four real DNS failure/absence results, including a silent UDP endpoint."""
+import socket
+import subprocess
+
+
+def query(server, name, kind="A", port=53):
+    command = ["dig", "@" + server, "-p", str(port), name, kind,
+               "+tries=1", "+time=2", "+noall", "+comments", "+answer", "+authority"]
+    print("\n$ " + " ".join(command), flush=True)
+    result = subprocess.run(command, capture_output=True, text=True)
+    print(result.stdout, end="", flush=True)
+    return result
+
+
+def main():
+    nx = query("resolver", "missing.lab.test")
+    nodata = query("resolver", "orders.lab.test", "AAAA")
+    failed = query("resolver", "name.broken.test")
+    # A bound UDP socket receives packets but sends nothing back: no ICMP port-unreachable.
+    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as silent:
+        silent.bind(("127.0.0.1", 0))
+        timeout = query("127.0.0.1", "orders.lab.test", port=silent.getsockname()[1])
+    assert "status: NXDOMAIN" in nx.stdout
+    assert "status: NOERROR" in nodata.stdout and "ANSWER: 0" in nodata.stdout
+    assert "status: SERVFAIL" in failed.stdout
+    assert timeout.returncode == 9 and "timed out" in timeout.stdout
+    print("PASS: NXDOMAIN / NODATA / SERVFAIL / timeout")
+
+
+if __name__ == "__main__":
+    main()