DHCP SnoopingA DHCP client can run on a switch simultaneously with the DHCP snooping feature as follows:• If you enable DHCP snooping globally on a switch and you enable a DHCP client on an interface, the trust port, source MAC address,and snooping table validations are not performed on the interface by DHCP snooping for packets destined to the DHCP client daemon.The following criteria determine packets destined for the DHCP client:• DHCP is enabled on the interface.• The user data protocol (UDP) destination port in the packet is 68.• The chaddr (change address) in the DHCP header of the packet is the same as the interface’s MAC address.• An entry in the DHCP snooping table is not added for a DHCP client interface.DHCP ServerA switch can operate as a DHCP client and a DHCP server. DHCP client interfaces cannot acquire a dynamic IP address from the DHCPserver running on the switch. Acquire a dynamic IP address from another DHCP server.Virtual Router Redundancy Protocol (VRRP)Do not enable the DHCP client on an interface and set the priority to 255 or assign the same DHCP interface IP address to a VRRP virtualgroup. Doing so guarantees that this router becomes the VRRP group owner.To use the router as the VRRP owner, if you enable a DHCP client on an interface that is added to a VRRP group, assign a priority less than255 but higher than any other priority assigned in the group.Configure the System for User Port Stacking (Option230)Set the stacking-option variable to provide stack-port detail on the DHCP server when you set the DHCP offer. A stack can be formedwhen the units are connected.Option 230 is the option for user port stacking. Use it to create up to eight stack groups. Define the configuration parameters on the DHCPserver for each chassis based on the chassis MAC address. Configure the following parameters:• unit number• priority• stack group IDThe received stacking configuration is always applied on the master stack unit.option #230 "unit-number:3#priority:2#stack-group:14"Configure Secure DHCPDHCP as defined by RFC 2131 provides no authentication or security mechanisms. Secure DHCP is a suite of features that protectsnetworks that use dynamic address allocation from spoofing and attacks.• Option 82• DHCP Snooping• Dynamic ARP Inspection296 Dynamic Host Configuration Protocol (DHCP)
