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DHCP snooping is a critical security feature that prevents unauthorized DHCP servers from distributing IP addresses to clients. By inspecting and filtering DHCP traffic, it ensures only legitimate DHCP servers can assign IP addresses, typically enforced at the switch level.
How DHCP Snooping Works
1. Trusted and Untrusted Ports Configuration
- Trusted ports allow DHCP server responses.
- Untrusted ports drop rogue DHCP server messages.
2. DHCP Packet Validation
- Filters DHCP messages to verify legitimacy.
- Blocks malicious DHCP offers from unauthorized servers.
3. DHCP Binding Database
- Maintains a record of assigned IP-MAC-port mappings.
- Prevents IP spoofing and man-in-the-middle attacks.
You Should Know: DHCP Snooping Configuration & Verification
Cisco Switch Configuration
Enable DHCP snooping globally Switch(config) ip dhcp snooping Enable snooping on a VLAN Switch(config) ip dhcp snooping vlan 10 Designate trusted ports (connected to legitimate DHCP servers) Switch(config-if) ip dhcp snooping trust Limit DHCP rate to prevent flooding Switch(config-if) ip dhcp snooping limit rate 10
Verification Commands
Check DHCP snooping status Switch show ip dhcp snooping View DHCP binding table Switch show ip dhcp snooping binding Check for rogue DHCP servers Switch show ip dhcp snooping statistics
Linux (Using `dhcpdump` for Monitoring)
Install dhcpdump sudo apt install dhcpdump Capture and analyze DHCP traffic sudo dhcpdump -i eth0
Windows (Detecting Rogue DHCP Servers)
List all DHCP servers in the network netsh dhcp show server Check authorized DHCP servers Get-DhcpServerInDC
What Undercode Say
DHCP snooping is essential for securing enterprise networks against rogue DHCP attacks. Implementing it with proper trusted port configurations and monitoring ensures IP integrity. Additional hardening techniques include:
– Dynamic ARP Inspection (DAI) to prevent ARP spoofing.
– Port Security to restrict MAC address changes.
– Network Segmentation to limit attack surfaces.
For deeper security, combine DHCP snooping with:
Enable DAI alongside DHCP snooping Switch(config) ip arp inspection vlan 10 Validate ARP packets using DHCP binding Switch(config) ip arp inspection validate src-mac dst-mac ip
Expected Output:
A secure network where only authorized DHCP servers operate, with logs confirming blocked rogue attempts.
Prediction: As IoT devices proliferate, DHCP snooping will become even more critical in preventing unauthorized IP assignments in smart environments.
Reference: High-Res Networking PDFs
References:
Reported By: Xmodulo Dhcp – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
