Network slowdowns manifest in various ways - from delayed file transfers to sluggish intranet browsing. Before diving into solutions, let's establish proper monitoring first.

Start with these terminal commands to gather baseline metrics:

# Continuous ping test
ping -t [server_IP] 

# Network interface statistics
netstat -i 

# TCP connection details
netstat -s -t

Add DNS lookup timing to your diagnostics. Here's a Python example:

import dns.resolver
import time

def check_dns(hostname):
    start = time.time()
    answers = dns.resolver.resolve(hostname)
    return time.time() - start
    
print(f"DNS resolution time: {check_dns('your-intranet-site.com')} seconds")

For Windows environments, capture traffic with PowerShell:

# Start packet capture
New-NetCaptureSession -CaptureType Physical -LocalIP Any -RemoteIP Any -SaveOnStop

# After reproduction period
Stop-NetCaptureSession

Implement connection pooling for HTTP requests. Node.js example:

const http = require('http');
const agent = new http.Agent({
  keepAlive: true,
  maxSockets: 10,
  maxFreeSockets: 5,
  timeout: 60000
});

const options = {
  hostname: 'intranet-server',
  port: 80,
  path: '/resource',
  method: 'GET',
  agent: agent
};

For SMB/CIFS shares, adjust these registry settings:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters]
"DisableBandwidthThrottling"=dword:00000001
"FileInfoCacheEntriesMax"=dword:00000100
"DirectoryCacheEntriesMax"=dword:00000100

Create a simple bandwidth test script:

# PowerShell bandwidth test
$source = "\\server\share\testfile.dat"
$dest = "C:\temp\testfile.dat"
Measure-Command { Copy-Item $source $dest } | Select-Object TotalSeconds

For web applications, implement proper caching headers:

// Express.js middleware example
app.use((req, res, next) => {
  res.set('Cache-Control', 'public, max-age=3600');
  next();
});

When users report sluggish network performance, we typically see symptoms like:

• File transfers stalling at particular percentages
• Inconsistent ping response times (e.g., alternating between 2ms and 500ms)
• TCP retransmissions visible in packet captures

Start with these command-line utilities that every developer should have in their toolkit:

# Continuous ping test (Linux/Mac)
ping -i 0.2 -c 100 destination_host | tee ping_results.log

# Windows equivalent
Test-NetConnection -ComputerName server -TraceRoute -InformationLevel Detailed

# Bandwidth measurement with iPerf3
iperf3 -c server.example.com -t 30 -P 8  # 8 parallel streams for 30 seconds

Wireshark filters for common network issues:

# High latency between SYN and SYN-ACK
tcp.flags.syn==1 && tcp.flags.ack==0 && frame.time_delta > 0.5

# Retransmissions
tcp.analysis.retransmission || tcp.analysis.fast_retransmission

# Window size issues
tcp.window_size < 1460 && tcp.len > 0

Here's a Python script to test HTTP request latency:

import requests
import time

def test_endpoint(url, iterations=10):
    latencies = []
    for _ in range(iterations):
        start = time.time()
        try:
            r = requests.get(url, timeout=5)
            latency = (time.time() - start) * 1000
            latencies.append(latency)
            print(f"Status {r.status_code} - {latency:.2f}ms")
        except Exception as e:
            print(f"Error: {str(e)}")
    
    if latencies:
        avg = sum(latencies)/len(latencies)
        print(f"\nAverage latency: {avg:.2f}ms")

test_endpoint("http://intranet/internal_api")

Common DNS issues can masquerade as network problems:

# Check DNS resolution times
dig +stats intranet.example.com
nslookup -debug intranet.example.com

# Flush local DNS cache (Windows)
ipconfig /flushdns

# Linux systemd-resolved
sudo systemd-resolve --flush-caches

For Linux servers handling many connections, consider these sysctl tweaks:

# Increase TCP window sizes
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216

# Improve congestion control
net.ipv4.tcp_congestion_control = bbr

# Reuse TIME-WAIT sockets
net.ipv4.tcp_tw_reuse = 1

For Wi-Fi networks, these commands help identify issues:

# Linux wireless tools
iwconfig wlan0
iw dev wlan0 scan | grep -i signal

# Windows equivalent
netsh wlan show interfaces
netsh wlan show networks mode=bssid

A simple bash script to monitor interface traffic:

#!/bin/bash

IFACE="eth0"
INTERVAL=5

while true; do
    RX1=$(cat /sys/class/net/$IFACE/statistics/rx_bytes)
    TX1=$(cat /sys/class/net/$IFACE/statistics/tx_bytes)
    sleep $INTERVAL
    RX2=$(cat /sys/class/net/$IFACE/statistics/rx_bytes)
    TX2=$(cat /sys/class/net/$IFACE/statistics/tx_bytes)
    
    RX=$(( (RX2 - RX1) / INTERVAL / 1024 ))
    TX=$(( (TX2 - TX1) / INTERVAL / 1024 ))
    
    echo "RX: $RX KB/s | TX: $TX KB/s | $(date)"
done