176 | Dynamic Host Configuration Protocol (DHCP)
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DHCP Client Operation with other Features
Stacking
The DHCP client daemon runs only on the master unit and handles all DHCP packet transactions. The
DHCP client running on the master unit periodically synchronizes the lease file with the standby unit.
When a stack failover occurs, the new master requests the same DHCP server-assigned IP address on
DHCP client interfaces. On non-bound interfaces, the new master re-initiates a DHCP packet transaction
by sending a DHCP discovery packet.
VLT
A DHCP client is not supported on VLT interfaces.
VLAN and Port Channels
DHCP client configuration and behavior is the same on port-channel (LAG) and VLAN interfaces as on a
physical interface.
DHCP Snooping
A DHCP client can run at the same on a switch with the DHCP snooping feature as follows:
• If you enable DHCP snooping globally on the switch and 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.
Packets destined for the DHCP client are determined by following criteria:
• DHCP is enabled on the interface
• UDP destination port in the packet is 68.
• chaddr in the DHCP header of the packet is the same as the interface’s MAC address.
• An entry in te 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 with the exception that a DHCP client interface
does not acquire a dynamic IP address from the DHCP server running on the switch. A dynamic IP address
must be acquired from another DHCP server.
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