Optimal Network Traffic Monitoring Solutions for Enterprise T3 Line Bottlenecks: A Programmer’s Guide to Bandwidth Analysis


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When 28 users share a T3 line (45 Mbps) and experience daytime slowdowns, the culprit is typically one of these scenarios:

  • Background updates (Windows Update, Dropbox sync)
  • P2P traffic from unaware users
  • Video streaming during work hours
  • Malware/compromised devices

1. SNMP-Based Monitoring (Quick Setup)

# Python example using PySNMP
from pysnmp.hlapi import *

for (errorIndication,
     errorStatus,
     errorIndex,
     varBinds) in nextCmd(SnmpEngine(),
                          CommunityData('public'),
                          UdpTransportTarget(('router_ip', 161)),
                          ContextData(),
                          ObjectType(ObjectIdentity('IF-MIB', 'ifInOctets')),
                          lexicographicMode=False):
    if errorIndication:
        print(errorIndication)
    elif errorStatus:
        print(errorStatus)
    else:
        for varBind in varBinds:
            print(varBind)

2. Deep Packet Inspection (DPI)

For protocol-level analysis:

// C++ example using libpcap
pcap_t *handle = pcap_open_live("eth0", BUFSIZ, 1, 1000, errbuf);
struct pcap_pkthdr header;
const u_char *packet = pcap_next(handle, &header);
// Analyze packet headers here
pcap_close(handle);

Recommended Tools:

Tool Best For Protocols Supported
PRTG SNMP monitoring HTTP, FTP, VoIP
Wireshark Packet analysis All Layer 7 protocols
ntopng Real-time traffic 2000+ application protocols

Sample Cisco IOS QoS configuration:

class-map match-any P2P-TRAFFIC
 match protocol bittorrent
 match protocol edonkey
 
policy-map LIMIT-P2P
 class P2P-TRAFFIC
  police 1000000 conform-action transmit exceed-action drop

interface FastEthernet0/0
 service-policy output LIMIT-P2P

Python script for threshold-based alerts:

import psutil, smtplib

def check_bandwidth(interface, threshold=70):
    stats = psutil.net_io_counters(pernic=True)[interface]
    total = stats.bytes_sent + stats.bytes_recv
    time.sleep(1)
    new_stats = psutil.net_io_counters(pernic=True)[interface]
    new_total = new_stats.bytes_sent + new_stats.bytes_recv
    usage = ((new_total - total) / 1000000) * 8  # Mbps
    
    if usage > threshold:
        send_alert(f"Bandwidth threshold exceeded: {usage} Mbps")

def send_alert(message):
    server = smtplib.SMTP('smtp.example.com', 587)
    server.starttls()
    server.login("admin@example.com", "password")
    server.sendmail("admin@example.com", "it-team@example.com", message)

When a T3 line (45 Mbps) slows to a crawl for 28 users, the culprit is often hidden in the traffic patterns. Common offenders include:

  • Cloud backup services saturating upload
  • Automatic Windows updates during work hours
  • Streaming media consumption (Spotify/YouTube)
  • P2P file sharing applications

Here's a Python script using Scapy to capture bandwidth hogs:


from scapy.all import *
from collections import defaultdict
import time

bandwidth = defaultdict(int)

def packet_handler(pkt):
    if IP in pkt:
        src = pkt[IP].src
        dst = pkt[IP].dst
        bandwidth[(src, dst)] += len(pkt)

sniff(prn=packet_handler, timeout=60)

# Print top talkers
for flow, bytes in sorted(bandwidth.items(), key=lambda x: x[1], reverse=True)[:5]:
    print(f"{flow[0]} -> {flow[1]}: {bytes/1024:.2f} KB")

For deep protocol analysis, these Wireshark display filters are invaluable:


# Find large transfers
tcp.len > 1000 and frame.time >= "09:00:00" and frame.time <= "17:00:00"

# Detect video streaming
http.request.uri matches "googlevideo|videoplayback"

# Identify torrent traffic
bittorrent or dht or udp.port in {6881 6889 6969}

On enterprise routers (Cisco example):


class-map match-any NON_ESSENTIAL
 match protocol bittorrent
 match protocol netflix
 match dscp cs1

policy-map OFFICE_QOS
 class NON_ESSENTIAL
  bandwidth remaining percent 5
 class class-default
  bandwidth remaining percent 95

For those preferring GUI tools:

Tool Best For License
PRTG Historical trending Free (100 sensors)
ntopng Real-time flows Open source
Darkstat Lightweight BSD

Remember to check for:

  • Chromecasts auto-updating 4K screensavers
  • Dropbox/OneDrive continuous sync
  • VoIP calls using excessive bandwidth