רשת מאפס: IP, Subnet, Gateway

Every computer on a network needs an address. Like a house on a street — without an address you can't send it mail. This address is called an IP Address.

Four fundamental concepts

IP Address — the computer's address on the network, e.g. 192.168.10.25.
Subnet Mask — determines which part of the address is the 'street' (the network) and which part is the 'house number' (the computer).
Default Gateway — the router through which traffic goes to other networks and the internet.
DNS Server — translates names (dc01.lab.local) into IP addresses.

Checking the settings on a computer

# Display IP address, Gateway and DNS
ipconfig /all

# Check connectivity to the Gateway
Test-NetConnection 192.168.10.1

# Check that the Domain name resolves to an IP
Resolve-DnsName lab.local

powershell

Architecture and Theory — Under the Hood

Every device on the network is identified by three addresses: MAC (hardware, L2), IP (logical, L3), and sometimes also a DNS name. Subnet Mask defines which part of the IP is the 'street' (Network) and which 'house' (Host). Gateway = exit to other streets.

IPv4 = 32 bits (4 bytes). Example: 192.168.10.25/24 → network 192.168.10.0, hosts 1-254, broadcast .255.
Private networks (RFC1918): 10/8, 172.16/12, 192.168/16 — not routed on the internet.
When a device needs to contact an IP in the same subnet — it sends directly (ARP). For a different IP — via the Gateway.

Practical Configuration (PowerShell / GUI)

# Windows - All information in one screen
ipconfig /all
Get-NetIPConfiguration
Get-NetRoute -AddressFamily IPv4

# Set static IP
New-NetIPAddress -InterfaceAlias 'Ethernet' -IPAddress 10.0.0.20 -PrefixLength 24 -DefaultGateway 10.0.0.1
Set-DnsClientServerAddress -InterfaceAlias 'Ethernet' -ServerAddresses 10.0.0.10

# Basic checks
Test-NetConnection dc01 -Port 445
Resolve-DnsName dc01.corp.local

powershell

Real-world Scenarios in an Organization

User reports 'no internet' — order: ipconfig → ping Gateway → ping 8.8.8.8 → nslookup.
At home: The Router is DHCP + DNS + NAT + Firewall — everything on the same device.
In an organization: Each role runs on a separate server.

Troubleshooting and Diagnosis

APIPA (169.254.x.x) → no DHCP response.
Valid IP but no internet → ping to Gateway, then to 8.8.8.8, then nslookup — determine at which stage it broke.
Duplicate IP → Event 4198/4199, arp -a will show two MAC addresses for the same IP.

Glossary and Quick Command Line

/24 = 256 (254 hosts).
/30 = 4 (2 hosts) - Point-to-Point.
ping = L3, telnet <ip> <port> = L4, nslookup = DNS.
MAC does not leave the Subnet, IP does.

Networking from zero: IP, Subnet, Gateway

What you will learn here

Four fundamental concepts

Checking the settings on a computer

Check yourself