Networking Review

Ping

Tests if a host is reachable

ifconfig/ip a

Shows IP addresses of network interfaces

ip route

Shows routing table which contains paths to network destinations for IP traffic.

traceroute

Traces path packets take to reach host

netstat/ss

View open ports, connections, and listening services

nslookup/dig

Look up DNS info for a domain

hostname/hostname -I

Show the system’s hostname and IP addresses

curl/wget

Test HTTP requests

telnet

Test connectivity on a port

DCSP (Differentiated Services Code Point)

A field in the IP header used to label packets with priority levels so routers and switches know how to handle different types of network (Part of QoS)

Value 0 in IP packet header

No priority, normal traffic

Value 46 in IP packet header

Expedited Forwarding (EF)

Values 10-40 in IP packet header

Assured Forwarding (AF) prioritized but non-critical traffic

Value 8 in IP packet header

Low priority (CS1) background tasks

3 types of DNS queries

recursive, iterative, and non-recursive

Recursive DNS Query

DNS server (resolver) does all the work for you

If it cant find the IP, it sends back an error

Common in regular web browsing

Iterative DNS Query

If the DNS doesnt know the answer, it replies “Try asking the other server instead”

The client or resolver keeps following referrals until it finds the final answer

Non-recursive DNS query

Happens when a server already has the answer cached

No extra searching → returns the result immediately

DNS “A” Record

Maps a domain to IP

Required

example.com →93.184.216.34

DNS “Cname” Record

Maps domain to another domain

Optional

www.example.com → example.com

DNS (Domain Name System)

Translates human-readable domain names into IP addresses so computers can find each other on the internet.

The 4 DNS servers involved in loading a webpage

DNS Recursor
Rootname Server
TLD Nameserver
Authoritative Nameserver

DNS Recursor

A server that receives a DNS request from a user and does all the lookup steps needed to return the final IP address.

Authoritative Nameserver

holds the actual DNS records (like A and CNAME) for a domain and gives the final answer to DNS queries.

Rootname Server

It looks at the end of the domain name (the top-level domain like .com, .org, .net)
and sends the query to the correct TLD name server that handles that type of domain.

TLD Nameserver

A TLD (Top-Level Domain) name server is responsible for handling domains that end in a specific extension like .com, .org, .net, etc.

It doesn’t have the final IP, but it tells you which authoritative server does.

PXE Boot (Preboot Execution Environment)

Allows computer to boot from a network (rather than hard drive or USB)

Key Components of PXE Boot

PXE Client
DHCP Server
TFTP Server
Boot Image

What is the PXE Client

The computer you want to boot from the network

Can have multiple clients

Must have a Network Interface Card

Sends a DHCP broadcast to start PXE process

What does the DHCP server do in PXE Boot

Assigns IP addresses to the PXE clients

What does the TFTP server do in PXE Boot

Sends the bootloader client to the clinets

What do the boot files do in PXE Boost

Files needed to start and install the operating system

What’s the first step in PXE boot?

Choose a device to be the PXE server (any Linux machine).

What’s the second step in PXE boot?

Install a DHCP server to assign IPs and point to boot files.

What’s the third step in PXE boot?

Install a TFTP server to serve bootfiles (pxelinux.0) and OS files.

What’s the fourth step in PXE boot?

Add OS boot files to the PXE server.

What’s the fifth step in PXE boot?

Connect all clients to the same wired network.

What’s the sixth step in PXE boot?

Ensure every client has a PXE-capable NIC.

What’s the seventh step in PXE boot?

Power on clients — they’ll broadcast DHCP, get boot files, and start OS install.

What’s the first step in a DNS lookup?

You type a website (like example.com) into your browser.

What happens after you type a website into your browser?

The DNS resolver receives the request and prepares to search for the IP address.

What does the DNS resolver do first?

It queries a Root DNS server to figure out which top-level domain (.com, .org, etc.) to ask next.

What does the Root DNS server respond with?

The IP address of the TLD (Top Level Domain) server (like .com)

After getting the TLD server address, what does the resolver do?

It asks the TLD server where to find the nameserver for example.com.

What does the TLD server respond with?

The address of the authoritative nameserver for example.com.

What does the resolver ask the authoritative nameserver?

“What is the IP address for example.com?”

What does the authoritative nameserver reply with?

The correct IP address for the domain (e.g., 93.184.216.34).sdfb

What is Network File System (NFS) used for?

It lets computers share files over a network as if they were on the local machine.

In NFS, what is a "server"?

The machine that hosts (shares) the files or directories.

In NFS, what is a "client"?

A computer that accesses files shared by the NFS server.

What are common use cases for NFS?

Centralized storage, backups, shared home directories, and server clusters.

What is iSCSI (Internet Small Computer Systems Interface) used for ?

To transport block-level storage data over IP networks.

iSCSI vs NFS — what’s the key difference?

iSCSI provides block-level storage, while NFS provides file-level storage.

Is iSCSI storage treated like a local disk?

Yes — the operating system sees it as a local block device.

Why use iSCSI over traditional storage?

It's cheaper and easier to implement because it uses standard Ethernet networks.