Administrator Guide

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.
DHCP Relay When DHCP Server and Client are in
Different VRFs
When the DHCP server and DHCP clients belong to different VRFs on the relay agent, you can configure the system to leak routes across
VRFs.
You can configure the system to leak the following routes across VRFs:
• Connected routes
• The complete routing table
• Selective routes
The following illustration depicts the topology in which routes are leaked between VRFs in the relay agent.
VRF_1 VRF_2
DHCP Server --------------------- DHCP relay agent --------------------------- Client
(10.0.0.1) (10.0.0.2) (20.0.0.2) (20.0.0.4)
320
Dynamic Host Configuration Protocol (DHCP)