Afternoon Session: Networking Basics

1. IP Addressing, Subnetting, and DNS Configuration

IPv4 Basics:
- An IP address is a unique identifier for a device on a network.
- It consists of four octets (e.g., 192.168.1.1) and follows the format of X.X.X.X, where X ranges from 0 to 255.
- Classes: A (1.0.0.0 to 126.255.255.255), B (128.0.0.0 to 191.255.255.255), C (192.0.0.0 to 223.255.255.255), D (Multicast), E (Experimental).
- Private IP Ranges:
  - 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
- Public vs. Private IPs: Private IPs are used within local networks, while public IPs are routable over the internet.
IPv6 Basics:
- A 128-bit address written in hexadecimal format (e.g., 2001:0db8:85a3::8a2e:0370:7334).
- Supports a much larger number of unique addresses.
- Designed to replace IPv4 due to address exhaustion.

Subnet Mask:
- Defines which portion of the IP address is the network and which is the host.
- Example: 255.255.255.0 means the first three octets represent the network, and the last octet represents hosts.
CIDR Notation:
- Written as IP/Prefix (e.g., 192.168.1.0/24).
- /24 means the first 24 bits are for the network, leaving 8 bits for host addresses.
Subnetting Example:
- If we divide 192.168.1.0/24 into two subnets:
  - 192.168.1.0/25 (First half: 192.168.1.1 to 192.168.1.126)
  - 192.168.1.128/25 (Second half: 192.168.1.129 to 192.168.1.254)
- This allows better allocation of IPs within large networks.

How DNS Works:
- Translates domain names (e.g., google.com) into IP addresses.
- Uses a hierarchy of DNS servers (Root, TLD, and Authoritative).
Types of DNS Records:
- A (Address Record) – Maps a domain to an IPv4 address.
- AAAA – Maps a domain to an IPv6 address.
- CNAME (Canonical Name) – Redirects one domain to another.
- MX (Mail Exchange) – Defines mail servers for a domain.
- PTR (Pointer Record) – Reverse DNS lookup.
Setting Up a Local DNS Server:
- Install a DNS server package (bind9 on Linux).
- Configure /etc/bind/named.conf.local to define zones.
- Add zone files (/var/named/example.com.zone) with DNS records.
- Restart the DNS service and test using nslookup or dig.

At least two computers (or virtual machines).
A router or switch (or software-defined networking tools like VirtualBox’s NAT).
Network cables (if using physical machines).

Assign Static IPs (or use DHCP for automatic IP assignment).
- Example:
  - PC1: 192.168.1.10/24
  - PC2: 192.168.1.11/24
  - Gateway (Router): 192.168.1.1/24
Enable DHCP Server on one machine (if required):
- Install isc-dhcp-server on Linux.
- Configure /etc/dhcp/dhcpd.conf:
```
subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.50 192.168.1.100;
    option routers 192.168.1.1;
    option domain-name-servers 8.8.8.8;
}
```
- Restart the DHCP service: sudo systemctl restart isc-dhcp-server.
Enable DNS Resolution:
- Set primary DNS server to 192.168.1.1 on all devices.
- Verify DNS resolution using nslookup example.com.
Network Connectivity Test:
- Ping test between machines: ping 192.168.1.11 from 192.168.1.10.
- Check default gateway: ip route show.

Disable firewall temporarily: sudo ufw disable (Linux) or netsh advfirewall set allprofiles state off (Windows).
Add firewall rules to allow necessary traffic.