Dynamic Host Configuration Protocol (DHCP) Snooping

Dynamic Host Configuration Protocol (DHCP) snooping is a security feature implemented in network switches to mitigate DHCP-related security threats. DHCP is responsible for dynamically assigning IP addresses to network devices, but it can be vulnerable to malicious attacks like DHCP spoofing and rogue DHCP servers.

The Purpose of DHCP Snooping

DHCP snooping helps prevent unauthorized devices or rogue DHCP servers from distributing IP addresses on the network. It ensures that only authorized DHCP servers can provide valid IP configurations to client devices, enhancing network security and integrity.

How DHCP Snooping Works

DHCP snooping operates by inspecting DHCP messages exchanged between DHCP clients (devices requesting IP addresses) and DHCP servers (devices providing IP addresses). Here's how it works:

1. Trusted and Untrusted Ports: Switch ports are classified as trusted or untrusted. Trusted ports are typically connected to authorized DHCP servers, while untrusted ports are connected to DHCP clients or other network devices.
2. Binding Database: The switch maintains a binding database that maps the MAC addresses of DHCP clients to the IP addresses they receive from the authorized DHCP servers.
3. DHCP Snooping Table: The switch uses the binding database to create a DHCP snooping table, which contains information about the DHCP clients, their associated IP addresses, and the switch ports to which they are connected.
4. DHCP Message Inspection: When DHCP messages traverse the switch, DHCP snooping inspects them. If a DHCP message is received on an untrusted port or if it does not match any entry in the DHCP snooping table, the switch discards the message.
5. Protection against Attacks: DHCP snooping prevents DHCP spoofing attacks, where unauthorized devices try to act as DHCP servers and assign invalid IP configurations to unsuspecting clients. It also protects against rogue DHCP servers that may attempt to provide malicious IP settings to clients.

Configuring DHCP Snooping

To enable DHCP snooping, network administrators need to configure the feature on the switch. They must designate trusted ports where authorized DHCP servers are connected and mark other ports as untrusted to prevent unauthorized DHCP servers from operating.

Conclusion

DHCP snooping is an essential security feature that helps safeguard networks from DHCP-related threats. By preventing unauthorized devices from distributing IP configurations and detecting rogue DHCP servers, DHCP snooping enhances network security, ensuring that IP address assignments are legitimate and valid.