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What Is DHCP Snooping, all things you should know



This article introduces what is DHCP Snooping, how it works, attacks that can be defended against, and how to enable DHCP Snooping.

DHCP Snooping is a security feature that helps protect a network from rogue DHCP (Dynamic Host Configuration Protocol) servers and other DHCP-based attacks. It is a technology that provides an additional layer of protection to network infrastructure by allowing only authorized devices to obtain IP addresses dynamically. In this article, we'll take a deep dive into what DHCP Snooping is, how it works, and the types of attacks it can protect against.

Cisco Systems. (n.d.). DHCP Snooping Configuration Guide, Cisco IOS Release 12.2SX. Retrieved from www.Cisco.com

What is DHCP?

Before diving into DHCP Snooping, let's understand what DHCP is. DHCP (Dynamic Host Configuration Protocol) is a network protocol that automatically assigns IP addresses to devices on the network. A DHCP server dynamically assigns IP addresses, subnet masks, default gateways, and other network configuration parameters to network devices. DHCP simplifies IP address management on a network by automatically assigning IP addresses as needed.

Leslie. (n.d.). DHCP Meaning. QSFPTEK. Retrieved April 12, 2023, from PPPoE vs DHCP

What is DHCP Snooping?

DHCP Snooping is a network security technique that prevents malicious attacks through the Dynamic Host Configuration Protocol (DHCP). Enabled on a switch, it records DHCP exchanges on each port of the network and stores them in a DHCP Snooping table, which shows which MAC addresses leased which IP addresses and when will expire. It can also prevent DHCP server spoofing attacks, thus improving network security and reliability by effectively preventing various malicious attacks.


How Does IP DHCP Snooping Work?

What are DHCP Spoofing Attacks?

When using the DHCP protocol to assign IP addresses to hosts in a network, attackers can exploit DHCP Spoofing attacks to send fake DHCP messages, deceiving hosts to connect to malicious DHCP servers controlled by the attacker. This can cause hosts to fail to connect to the network or redirect them to malicious websites for further attacks.

How to Prevent DHCP Spoofing Attacks


To address this problem, DHCP Snooping technology was developed. Enables the network switch by enabling DHCP Snooping, dividing DHCP ports into Trusted and Untrusted ports, and learning all MAC and IP addresses that pass through Trusted ports. When a DHCP message arrives at an Untrusted port, the switch verifies whether it's source MAC and IP addresses match those in the dynamic database. If they do not match, the switch discards the message, thereby preventing DHCP Spoofing attacks. DHCP Snooping typically divides interfaces on switches into trusted ports and untrusted ports.

DHCP Spoofing Attack

How to Prevent DHCP Server Poisoning

In addition, DHCP Snooping technology can also prevent DHCP servers from being poisoned. The switch learns all MAC and IP addresses of DHCP servers that pass through Trusted ports and stores them in a dynamic database. If the DHCP message contains a DHCP server IP address that does not match a known DHCP server IP address in the dynamic database, the switch discards the message to prevent attackers from poisoning DHCP servers and sending false IP addresses to hosts in the network.


Finally, the switch logs all DHCP messages that do not pass verification in the DHCP Snooping log so administrators can view them and take necessary actions. This way, it can effectively protect network security and prevent DHCP attacks.

DHCP Snooping prevent DHCP servers from being poisoned

What Attacks Can DHCP Snooping Defend Against?

Rogue DHCP servers

DHCP Snooping is primarily designed to defend against rogue DHCP servers. Rogue DHCP servers are devices that have been configured to distribute IP addresses to clients on a network without authorization. These devices can cause serious security problems, as they can be used to intercept network traffic or launch other types of attacks.

DHCP Snooping can defend against rogue DHCP servers by blocking DHCP messages that originate from untrusted sources. When an untrusted host sends a DHCP message, the switch will inspect the message and compare it to the DHCP binding table. The switch will drop the message if the source MAC address is not in the DHCP binding table. This prevents unauthorized hosts from distributing IP addresses on the network.

DHCP Spoofing and DHCP Starvation

DHCP Snooping can also defend against DHCP-based attacks, such as DHCP spoofing and DHCP starvation. DHCP spoofing is a type of attack where an attacker sends fake DHCP messages to a network in an attempt to hijack IP addresses. DHCP starvation is an attack where an attacker floods the network with DHCP requests, causing the DHCP server to run out of available IP addresses.

How to Enable DHCP Snooping and Its Benefits

Enable DHCP

To enable DHCP Snooping on a network, you must first configure the DHCP server to provide valid IP addresses and other network configuration parameters. Then, you must configure the switch to enable DHCP Snooping and specify the trusted DHCP servers and interfaces. You can also configure other DHCP Snooping features, such as DHCP rate limiting and DHCP option filtering, to further enhance network security.

DHCP’s Benefits

There are several benefits of using DHCP Snooping in a network environment. Some of the most significant benefits include:

Enhanced Network Security

It prevents rogue DHCP servers from distributing IP addresses to unauthorized devices, which helps to enhance network security.

Improved Network Reliability

It ensures that only authorized DHCP servers are used to assign IP addresses, which reduces the risk of IP address conflicts and network downtime.

Simplified Network Management

It makes it easier to manage IP addresses and network settings by automating the process of assigning IP addresses to devices.

QSFPTEK DHCP Snooping Devices

QSFPTEK offers a range of network devices with DHCP Snooping functionality, including the S7600-48Y8C, S7600-24Y4C, and S7600-24X2C from the S7600 series, as well as switches from the S7300 series. These devices provide additional features beyond DHCP support, such as Quality of Service (QoS) and Access Control Lists (ACL) to ensure secure data transmission. In addition to QoS and ACL capabilities, the S7300 series switches also come equipped with DDoS protection for increased network security.


In conclusion, DHCP Snooping is an essential security feature that protects networks from rogue DHCP servers and other DHCP-based attacks. QSFPTEK offers a range of devices that support DHCP Snooping functionality, making it easy for network administrators to implement this technology and enjoy its numerous benefits. With it, networks can be safeguarded against potential attacks and operate smoothly, ensuring that data is transmitted securely and efficiently.



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