add script to test max MTU

2026-01-19 08:59:23 +01:00
parent bd3f6c0b17
commit 111c1437be
4 changed files with 91 additions and 17 deletions
@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+
+import sys
+import subprocess
+
+
+def ping(host, packet_size, is_ipv6=False):
+    if is_ipv6:
+        header_size = 48  # 40 bytes IPv6 header + 8 bytes ICMPv6 header
+        cmd = ['ping', '-6', '-c', '2', '-M', 'do', '-s', str(packet_size - header_size), host]
+    else:
+        header_size = 28  # 20 bytes IP header + 8 bytes ICMP header
+        cmd = ['ping', '-4', '-c', '2', '-M', 'do', '-s', str(packet_size - header_size), host]
+
+    try:
+        result = subprocess.run(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        return result.returncode == 0
+    except Exception:
+        return False
+
+
+def bin_search_mtu(host, min_mtu, max_mtu, is_ipv6=False):
+    l = min_mtu
+    h = max_mtu
+    ret = 0
+
+    print(f"Testing {'IPv6' if is_ipv6 else 'IPv4'} MTU for {host}...")
+
+    if not ping(host, l, is_ipv6):
+        print(f"  Cannot reach host even with MTU {l}.")
+        return None
+
+    while l <= h:
+        m = (l + h) // 2
+        if ping(host, m, is_ipv6):
+            ret = m
+            print(f"  MTU {m} OK")
+            l = m + 1
+        else:
+            print(f"  MTU {m} Failed")
+            h = m - 1
+
+    return ret
+
+
+def main():
+    if len(sys.argv) < 2 or len(sys.argv) == 3 or len(sys.argv) > 4:
+        print(f"Usage: {sys.argv[0]} <domain> [min_mtu max_mtu]")
+        sys.exit(1)
+
+    domain = sys.argv[1]
+    min_search = sys.argv[2] if len(sys.argv) >= 4 else 1000
+    max_search = sys.argv[3] if len(sys.argv) >= 4 else 1500
+
+    ipv4_mtu = bin_search_mtu(domain, min_search, max_search, is_ipv6=False)
+    if ipv4_mtu:
+        print(f"Max IPv4 MTU: {ipv4_mtu}")
+    else:
+        print("Could not determine IPv4 MTU.")
+
+    print("-" * 20)
+
+    ipv6_mtu = bin_search_mtu(domain, min_search, max_search, is_ipv6=True)
+    if ipv6_mtu:
+        print(f"Max IPv6 MTU: {ipv6_mtu}")
+    else:
+        print("Could not determine IPv6 MTU.")
+
+
+if __name__ == "__main__":
+    main()