Implement more detailed bandwidth monitoring

modules/nagios/files/check_bandwidth

 #!/usr/bin/env python
 
 import os, re, subprocess, sys, socket, struct, fcntl
 
 INTERVAL = 5
 
 def format_bandwidth(bits):
   if bits >= 1000000:
     return "%.2f Mbit/s" % (bits / 1000000)
   elif bits >= 1000:
     return "%.2f kbit/s" % (bits / 1000)
   else:
     return "%.2f bit/s" % bits
 
 def getmacaddress():
-  # We are calling SIOCGIFHWADDR (0x8927 according to man ioctl_list) here. See
-  # man netdevice for the request structure: it has to start with 16 bytes
+  # See man netdevice for the request structure: it has to start with 16 bytes
   # containing the interface name, the OS will write 8 bytes after that (2 bytes
   # family name and 6 bytes actual MAC address).
   s = socket.socket()
-  return fcntl.ioctl(s.fileno(), 0x8927, struct.pack("24s", "eth0"))[18:24]
-
-def readtime(time):
-  hour, minute, second = time.split(":")
-  return int(hour) * 3600 + int(minute) * 60 + float(second)
+  SIOCGIFHWADDR = 0x8927   # see man ioctl_list
+  return fcntl.ioctl(s.fileno(), SIOCGIFHWADDR, struct.pack("24s", "eth0"))[18:24]
 
 if __name__ == "__main__":
   if len(sys.argv) != 3:
     script_name = os.path.basename(sys.argv[0])
     print "Usage: %s WARN CRIT" % script_name
     sys.exit(0)
 
   (warn, crit) = sys.argv[1:3]
   warn = int(sys.argv[1])
   crit = int(sys.argv[2])
 
-  process = subprocess.Popen(["sudo", "tcpdump", "-q", "-n", "-s", "64", "-w", "-"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-  starttime = None
+  process = subprocess.Popen(
+    ["sudo", "tcpdump", "-q", "-s", "64", "-G", str(INTERVAL), "-W", "1", "-w", "-"],
+    stdout=subprocess.PIPE, stderr=subprocess.PIPE)
   mac = getmacaddress()
 
   total = {"rx": 0, "tx": 0}
   http = {"rx": 0, "tx": 0}
   https = {"rx": 0, "tx": 0}
   ssh = {"rx": 0, "tx": 0}
   dns = {"rx": 0, "tx": 0}
   other = {"rx": 0, "tx": 0}
   other_detailed = {}
 
   # See http://wiki.wireshark.org/Development/LibpcapFileFormat for libpcap format description
-  magic_number, _, _, _, _, _, _ = struct.unpack("IHHiIII", process.stdout.read(24))
+  global_header = process.stdout.read(24)
+  magic_number, _, _, _, _, _, _ = struct.unpack("IHHiIII", global_header)
   if magic_number != 0xa1b2c3d4:
     raise Exception("Unexpected format")
   while True:
-    sec, usec, incl_len, orig_len = struct.unpack("IIII", process.stdout.read(16))
+    record_header = process.stdout.read(16)
+    if record_header == "":
+      break;
+    _, _, incl_len, orig_len = struct.unpack("IIII", record_header)
 
     # Convert bytes to bits and normalize to seconds
-    length = float(orig_len * 8) / INTERVAL
-
-    time = sec + float(usec) / 1000000
-    if starttime == None:
-      starttime = time
-    if time - starttime > INTERVAL:
-      break
+    bps = float(orig_len * 8) / INTERVAL
 
     def add_other(description):
-      other[direction] += length
-      other_detailed[description] = other_detailed.get(description, 0) + length
+      other[direction] += bps
+      other_detailed[description] = other_detailed.get(description, 0) + bps
 
     payload = process.stdout.read(incl_len)
 
     # Unpack Ethernet frame, http://en.wikipedia.org/wiki/Ethernet_frame#Structure
+    # Note that tcpdump doesn't capture the preamble, start of frame delimiter
+    # and the interframe gap, these are handled internally by the network card.
     destination, source, protocol = struct.unpack("!6s6sH", payload[:14])
     payload = payload[14:]
     direction = "rx" if destination == mac else "tx"
-    total[direction] += length
+    total[direction] += bps
 
     # Check Level 3 protocol
     if protocol == 0x0800:     # IPv4, http://en.wikipedia.org/wiki/Internet_Protocol_version_4#Header
       ihl = ord(payload[0]) & 0xF
       protocol = ord(payload[9])
       payload = payload[ihl * 4:]
     elif protocol == 0x86DD:   # IPv6, http://en.wikipedia.org/wiki/IPv6_packet#Fixed_header
       protocol = ord(payload[6])
       payload = payload[40:]
     else:
       add_other("L3 0x%04X" % protocol)
       continue
 
     # Check Level 4 protocol
     if protocol in (0x06, 0x11):    # TCP, UDP
+      source_port, destination_port = struct.unpack('!HH', payload[:4])
+      protocol = "TCP" if protocol == 0x06 else "UDP"
+
       # The lower port number should be the real port, the other one will be
       # the ephemeral port.
-      source_port, destination_port = struct.unpack('!HH', payload[:4])
-      protocol = "TCP" if protocol == 0x06 else "UDP"
       port = min(source_port, destination_port)
     else:
       add_other("L4 0x%02X" % protocol)
       continue
 
     if protocol == "TCP" and port == 80:
-      http[direction] += length
+      http[direction] += bps
     elif protocol == "TCP" and port == 443:
-      https[direction] += length
+      https[direction] += bps
     elif protocol == "TCP" and port == 22:
-      ssh[direction] += length
+      ssh[direction] += bps
     elif port == 53:
-      dns[direction] += length
+      dns[direction] += bps
     else:
       add_other("Port %i" % port)
       continue
 
   status = []
   perfdata = []
   def add_status(id, values):
     rx = values["rx"]
     tx = values["tx"]
     status.append("%srx %s %stx %s" % (id, format_bandwidth(rx), id, format_bandwidth(tx)))
@@ skipping 15 matching lines @@
 
   if total["rx"] >= crit or total["tx"] >= crit:
     print "CRITICAL - " + output
     sys.exit(2)
 
   if total["rx"] >= warn or total["tx"] >= warn:
     print "WARNING - " + output
     sys.exit(1)
 
   print "OK - " + output