DHCP snooping not enabled
At a glance
Base severity
Area
Platform
Evidence level
Benchmark reference
Reads the export, not the device
ConfigProof reads a configuration export. This control is evaluated against the objects in that file, and it reports what the file says. It does not connect to the device and sees no traffic, so a finding here describes the configuration, not what the firewall is doing right now.
Why it matters
A rogue DHCP server on any port can hand out a malicious gateway or DNS server to users in the VLAN.
How to fix it
Web interface
The steps below are written for the web interface. A finding raised on your own export carries the same steps with your object names filled in.
- Enable ip dhcp snooping and ip dhcp snooping vlan <vlans>, and mark only uplinks toward the real DHCP servers as trusted.
Command line
Cisco IOS-XE CLI
configure terminalip dhcp snooping vlan <user-vlans>ip dhcp snoopinginterface <uplink>ip dhcp snooping trustendwrite memory
An example. Values in angle brackets are yours to supply; a finding on your own export fills in the names it read. Typed in configuration mode; copy running-config startup-config saves it, with no separate commit. Read every line first.
Read it back
show ip dhcp snoopingValues to fill in2
- <user-vlans>
- The user VLANs
- <uplink>
- The uplink toward the DHCP servers
Before you type it3
- Written from the Cisco IOS-XE 17 and NX-OS 9 and 10 command references and not run on a device: read each line before you paste it.
- Trust only the ports toward the real DHCP servers and the uplinks; an untrusted uplink drops every client's DHCP.
- On a Nexus (NX-OS) switch the same change is typed with NX-OS syntax; check the NX-OS configuration guide for the equivalent command.
How to confirm the fix
- show ip dhcp snooping shows it enabled on the user VLANs.
Limits
- No limitation is recorded for this control beyond the one that applies to all of them: it reads a configuration export.
Compliance references
No benchmark recommendation is mapped to this control in this version.
More in Interfaces and Segmentation
- SW-SEC-006Edge ports without BPDU guard
- SW-SEC-007Ports negotiating trunking (DTP)
- SW-SEC-008Trunk native VLAN is VLAN 1
- SW-SEC-009Trunk carries every VLAN
- SW-SEC-010User ports in the default VLAN
- SW-SEC-012Dynamic ARP inspection not enabled
- SW-SEC-016VTP in server or client mode
- SW-SEC-017vPC peer link with no separate peer keepalive
See it on your own firewall
One complete analysis of one firewall costs nothing. A card is required and nothing is charged.