Dasar Networking dan TCP/IP

Memahami fundamental networking adalah kunci untuk menjadi network administrator yang kompeten.

Model OSI

OSI (Open Systems Interconnection) model terdiri dari 7 layers:

TCP/IP Stack

TCP/IP menggunakan 4 layers yang lebih sederhana:

1. Application Layer - HTTP, FTP, SMTP, DNS
2. Transport Layer - TCP, UDP
3. Internet Layer - IP, ICMP, ARP
4. Network Access Layer - Ethernet, Wi-Fi

IP Addressing

IPv4 Address Format

IPv4 address terdiri dari 32-bit, ditulis dalam 4 octet (0-255):

192.168.1.1
10.0.0.1
172.16.0.1

Kelas IP Address

IP Address Private

• Class A: 10.0.0.0 - 10.255.255.255
• Class B: 172.16.0.0 - 172.31.255.255
• Class C: 192.168.0.0 - 192.168.255.255

IP Address Khusus

• 127.0.0.1 - Loopback address (localhost)
• 0.0.0.0 - Default route
• 255.255.255.255 - Broadcast address
• 169.254.x.x - APIPA (Auto Configuration IP)

Subnetting

CIDR Notation

192.168.1.0/24  - 256 IP addresses
192.168.1.0/25  - 128 IP addresses
192.168.1.0/26  - 64 IP addresses
192.168.1.0/27  - 32 IP addresses

Cara Menghitung Subnet

Formula:

• Total IP = 2^(32 - subnet_bits)
• Usable IP = Total IP - 2 (network & broadcast)
• Subnet Mask = 255.255.255.(256 - 2^(32 - subnet_bits))

Contoh /26:

• Total IP = 2^6 = 64
• Usable IP = 62
• Subnet Mask = 255.255.255.192

Transport Layer Protocols

TCP (Transmission Control Protocol)

• Connection-oriented
• Reliable delivery
• Three-way handshake
• Flow control
• Error checking
• Contoh: HTTP, FTP, SMTP, SSH

Three-way Handshake:

1. SYN (Client -> Server)
2. SYN-ACK (Server -> Client)
3. ACK (Client -> Server)

UDP (User Datagram Protocol)

• Connectionless
• Unreliable (tanpa guarantee)
• Faster than TCP
• No flow control
• Contoh: DNS, DHCP, VoIP, Gaming

Port Numbers

Perintah Networking Dasar

Linux/Unix

ifconfig              # Cek interface network (deprecated)
ip addr show          # Cek interface network
ip route show         # Tampilkan routing table
ping host.example.com # Tes koneksi
traceroute host       # Trace path ke host
mtr host              # Combines ping & traceroute
netstat -tulpn        # Tampilkan listening ports
ss -tulpn             # Modern netstat
nslookup domain.com   # DNS lookup
dig domain.com        # Advanced DNS lookup

Windows

ipconfig              # Cek IP config
ipconfig /all         # Detail IP config
ping host.example.com # Tes koneksi
tracert host          # Trace path ke host
netstat -an           # Tampilkan connections
nslookup domain.com   # DNS lookup

ARP (Address Resolution Protocol)

ARP memetakan IP address ke MAC address.

# Lihat ARP table
arp -a

# Clear ARP cache
arp -d

DNS (Domain Name System)

DNS menerjemahkan domain name ke IP address.

Record Types

Tools

# Simple lookup
nslookup example.com

# Detailed lookup
dig example.com ANY

# Check MX record
dig example.com MX

# Reverse lookup
dig -x 192.0.2.1

Routing

Static Routing

# Linux
ip route add 192.168.2.0/24 via 192.168.1.254

# Windows
route add 192.168.2.0 mask 255.255.255.0 192.168.1.254

Default Gateway

# Set default gateway Linux
ip route add default via 192.168.1.1

# Set default gateway Windows
route add 0.0.0.0 mask 0.0.0.0 192.168.1.1

Firewall Basics

iptables

# List rules
iptables -L -n -v

# Allow HTTP
iptables -A INPUT -p tcp --dport 80 -j ACCEPT

# Drop all other
iptables -A INPUT -j DROP

UFW (Ubuntu)

ufw allow 22/tcp
ufw allow 80/tcp
ufw enable

Network Troubleshooting

Checklist

1. Cek kabel fisik
2. Cek IP configuration
3. Ping local gateway
4. Ping external IP (8.8.8.8)
5. Ping domain name
6. Cek DNS settings
7. Cek firewall rules
8. Cek routing table

Common Commands

# Check interface
ip link show

# Check IP address
ip addr show

# Test connectivity
ping -c 4 8.8.8.8

# Trace route
traceroute 8.8.8.8

# Check DNS
nslookup google.com

# Check listening ports
ss -tulpn

# Check connections
netstat -an

Kesimpulan

Memahami fundamental networking adalah pondasi penting untuk karir di IT. Latih konsep-konsep di atas dengan praktik langsung menggunakan lab virtual atau hardware yang tersedia.