The reader who was concerned about making a loop while connecting a switch to itself was also facing “customer-installed” DHCP servers in his LAN. He wrote:
Some users have installed their own Linksys routers and plug our cable in router's LAN ports, so there is DHCP servers fight in our LAN. How can I sort this out (I cannot physically find the location of the Linsys routers)?
- Enable the feature globally with the ip dhcp snooping global configuration command.
- Enable the feature for individual VLANs with the ip dhcp snooping vlan number global configuration command.
- Configure the trusted interfaces with the ip dhcp snooping trust interface configuration command.
- Rate-limit DHCP on untrusted interfaces with the ip dhcp snooping limit rate interface configuration command.