Master Sniffing with CEH Module 8

Have you ever wondered how Cyber Security Experts catch cyber attackers? One of the tools they use is network sniffing. Imagine you could listen to every conversation in a room to find out what’s being discussed; network sniffing is somewhat similar, but for computer networks. CEH Module 8: Sniffing is all about sniffing concepts, different sniffing techniques, and various techniques to detect sniffing attacks. In this article, let’s dive deeper into the sniffing concepts.

What is Network Sniffing?

As the name suggests, sniffing refers to the technique by which devices on a network can capture and analyze packets of data being transmitted over that network. Much like how a dog uses its sense of smell to gather information about its environment, network sniffing involves scanning the “digital scent” or data trails that flow across a network. This process allows sniffers (the tools or software used for sniffing) to listen in on network traffic, including emails, website visits, and other data transmissions.

Packet sniffing

Packet sniffing is like being at a busy post office where every package and letter being sent and received can be secretly checked to see where it’s coming from and what it might contain. In the digital world, these “packages” are known as data packets, and they travel across networks like the Internet or within a company’s private network.

In simple networks called hub-based networks, all data goes through a central point, making it easy to see all the data passing through. Most modern networks use devices called switches, which are more secure because they only send data directly from the sender to the receiver without being visible to everyone else.

However, someone who wants to spy on network traffic can trick the switch into sending them the data. This is usually done using a packet sniffing program known as a sniffer. Sniffers can’t see data from outside their own network area, but they can plug into the network and, if set up correctly, see all the traffic.

Different Sniffing Techniques

A sniffer captures data packets as they travel across a network. It works by intercepting these packets to view or analyze the transmitted data.

Shared Ethernet

• In a shared Ethernet environment, all hosts are connected through a single communication line (bus), competing for bandwidth. Each packet a device sends is seen by all other devices on the same network segment, but only the device with the matching MAC address will accept and process the packet.
• In Ethernet networks, data is sent in frames that include the MAC addresses of the sending and receiving devices. Sniffers use promiscuous mode on network interface cards (NICs) to listen to all traffic on the wire, regardless of the intended recipient.

Switched Ethernet

• In switched Ethernet, each switch port connects to a single MAC address, making it more secure than environments where messages are broadcast to multiple ports.
• However, this does not guarantee security from sniffing because if a device is compromised, an attacker can still capture packets directed to and from it.

MAC Flooding

• Switches use a translation table (CAM Table) to map MAC addresses to physical ports. However, this table has limited memory.
• MAC flooding happens when an attacker overloads a switch’s memory by sending numerous frames, each with a unique source MAC address. This forces the switch to act like a hub, broadcasting incoming packets to all ports, which then allows the attacker to sniff network traffic.

ARP Spoofing

• ARP (Address Resolution Protocol) is stateless, meaning it does not require prior communication to send or receive information.
• A device can send an ARP reply without being asked for it, which can lead to ARP spoofing. This occurs when a device sends a false ARP reply to another device, misleading it about the identity of another machine on the network. Consequently, the victim device sends its data to the attacker instead of the intended recipient.

Types of Sniffing

Sniffing is a technique used to monitor and capture data packets passing through a network. There are two main types of sniffing:

• Passive Sniffing: This method quietly captures network traffic without sending data packets. It’s mainly effective in networks that use hubs, where all data traffic is shared across all devices. In such environments, anyone can see all the traffic, making it easy to use passive sniffing to monitor what’s being transmitted.
• Active Sniffing: Unlike passive sniffing, active sniffing involves more interaction with the network. This type might send packets or manipulate the network to redirect or receive more traffic. It’s used in more complex network setups where passive sniffing wouldn’t see much traffic due to the network’s structure. Some of the active sniffing techniques include:
• MAC flooding
• DNS poisoning
• ARP poisoning
• DHCP attacks
• Switch port stealing

Understanding the fundamentals of how sniffing works, the different environments it can operate in, and the techniques employed, both passive and active, is crucial for anyone involved in network security. By familiarizing themselves with the methods used to sniff network traffic and the strategies used to defend against sniffing attacks, IT professionals can better safeguard sensitive information and maintain the integrity of their networks.

CEH with InfosecTrain

Understanding the intricate details of network sniffing, its techniques, and the methods attackers use to exploit vulnerabilities is essential for anyone involved in cybersecurity. Sniffing can uncover crucial insights into network traffic but poses significant risks if used maliciously. Whether it’s recognizing the difference between passive and active sniffing or learning to counteract threats like ARP spoofing and MAC flooding, a thorough grasp of these concepts is crucial for securing modern networks.

InfosecTrain’s Certified Ethical Hacker (CEH) training is meticulously designed to equip you with these critical skills. The course deepens into sniffing techniques, detection methods, and defensive strategies, providing hands-on experience to identify and mitigate network vulnerabilities. With expert trainers and practical learning approaches, InfosecTrain ensures you gain the expertise to protect organizations against advanced cyber threats.

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