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DHCP Client Operation with Other Features
A DHCP client also operates with the following software features.
Virtual Link Trunking (VLT)
A DHCP client is not supported on VLT interfaces.
VLAN and Port Channels
DHCP client configuration and behavior are the same on Virtual LAN (VLAN) and port-channel (LAG)
interfaces as on a physical interface.
DHCP Snooping
A 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 Server
A switch can operate as a DHCP client and a DHCP server. DHCP client interfaces cannot acquire a
dynamic IP address from the DHCP server 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 virtual group. 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 than 255 but higher than any other priority assigned in the group.
Configure Secure DHCP
The following feature is available on the platform, except where noted.
DHCP as defined by RFC 2131 provides no authentication or security mechanisms. Secure DHCP is a suite
of features that protects networks that use dynamic address allocation from spoofing and attacks.
• Option 82
• DHCP Snooping
• Dynamic ARP Inspection
Dynamic Host Configuration Protocol (DHCP)
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