2025/02/16

Topic 714: Basic BSD Network Administration

This topic covers network fundamentals and configuration on BSD systems. You will learn about IPv4 and IPv6 addressing, subnetting, and the roles of TCP, UDP, and ICMP. In addition, you'll see how to configure network interfaces (both statically and via DHCP), troubleshoot network issues, and set up client-side DNS. Detailed explanations and examples are provided below.

714.1: Basic BSD Network Administration

IPv4 Addressing

Concepts:
- Network address: The base address of a subnet (e.g., 192.168.1.0 in 192.168.1.0/24).
- Broadcast address: The address used to send data to all hosts on a subnet (e.g., 192.168.1.255 for 192.168.1.0/24).
- Subnetting: Dividing an IP network into smaller segments. With a /24 subnet mask (255.255.255.0), you have 256 addresses, typically 254 usable.
Example:
- For the network 192.168.1.0/24:
  - Network address: 192.168.1.0
  - Usable host range: 192.168.1.1 to 192.168.1.254
  - Broadcast address: 192.168.1.255

IPv6 Addressing

Concepts:
- Global address: Routable on the Internet (e.g., 2001:0db8:85a3::8a2e:0370:7334).
- Link-local address: Used for communication on the local network segment (typically starting with fe80::).
- Subnetting: Most IPv6 networks use a /64 subnet, which is standard.
Example:
- Global IPv6: 2001:0db8:85a3::8a2e:0370:7334
- Link-local: fe80::1
Note: IPv6 may use SLAAC or DHCPv6 for address assignment.

Network Protocols

TCP (Transmission Control Protocol):
Connection-oriented; ensures reliable, ordered delivery of data (e.g., HTTP, FTP).
UDP (User Datagram Protocol):
Connectionless; offers faster transmission with less overhead but no guarantee of delivery (e.g., DNS, streaming).
ICMP (Internet Control Message Protocol):
Used for sending error messages and operational information (e.g., ping for connectivity testing).

714.2: Basic Network Configuration

Static IP Assignment (FreeBSD Example)

Commands:

ifconfig em0 192.168.1.100 netmask 255.255.255.0
route add default 192.168.1.1

Explanation:
Sets the network interface em0 with a static IP (192.168.1.100) and a subnet mask of 255.255.255.0. The default gateway is set to 192.168.1.1 to enable external network access.

DHCP Configuration

Command:
```
dhclient em0
```
Explanation:
Requests an IP address from a DHCP server for the interface em0.

Persistent Configuration (FreeBSD)

File: /etc/rc.conf

ifconfig_em0="inet 192.168.1.100 netmask 255.255.255.0"
defaultrouter="192.168.1.1"

Explanation:
These settings ensure the static IP and default gateway are applied automatically at boot.

OpenBSD Configuration

Interface Configuration:
Edit /etc/hostname.em0 with:
```
inet 192.168.1.100 255.255.255.0
```
Default Gateway:
Edit /etc/mygate with:
```
192.168.1.1
```

714.3: Basic Network Troubleshooting

Checking Interfaces and Routing

Check interface status:
```
ifconfig
```
Displays status and configuration of all network interfaces.
View routing table:
```
netstat -rn
```
Shows the routing table in numeric format.

Testing Connectivity

Ping a host:
```
ping 8.8.8.8
```
Sends ICMP echo requests to test connectivity.
Traceroute:
```
traceroute 8.8.8.8
```
Traces the route packets take to reach the destination.

Checking Open Ports and Sockets

Nmap scan:
```
nmap localhost
```
Scans for open ports on the local system.
Netcat example:
```
nc -vz localhost 80
```
Checks if port 80 is open.
List listening sockets (FreeBSD/NetBSD):
```
sockstat -4
```
Lists all open IPv4 sockets.
IPv6 router solicitation:
```
rtsol em0
```
Sends an ICMPv6 Router Solicitation on interface em0 to discover routers.

Additional Troubleshooting

/etc/services file:
Contains mappings of port numbers to service names.
Router Solicitation Daemon (rtsol):
Automatically sends Router Solicitation messages to discover IPv6 routers.

714.4: Configure Client-Side DNS

DNS Resolver Configuration

Example /etc/resolv.conf:
```
nameserver 8.8.8.8
search example.com
```
Explanation:
Specifies the DNS server (8.8.8.8) and the default search domain (example.com).

Testing DNS Resolution

Using host:
```
host www.example.com
```
Resolves the IP address for www.example.com.
Using dig:
```
dig A www.example.com
```
Retrieves A records for www.example.com.
Using nslookup:
```
nslookup www.example.com
```
Another tool to query DNS records.

NSSwitch Configuration

Example /etc/nsswitch.conf:
```
hosts: files dns
```
Explanation:
Directs the system to first check local files (like /etc/hosts) then DNS for hostname resolution.

FreeBSD-Specific DNS Tools

drill:
A DNS lookup utility on FreeBSD that offers detailed output similar to dig.

Cristian Souza