Users Guide

○ 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.
Configuring DHCP relay source interface
The following section explains how to configure global and interface level DHCP relay source IPv4 or IPv6 configuration to
forward all the DHCP packets from the DHCP client to DHCP server through the configured source interface. This feature is
applicable only for L3 interface with relay configuration and L3 DHCP snooping enabled VLANs.
Global DHCP relay source IPv4 or IPv6 configuration
You can configure global DHCP relay source IPv4 or IPv6 configuration using the command {ip | ipv6} dhcp-relay
source-interface interface command in the CONFIGURATION mode. DHCP relay uses the IPv4 or IPv6 global source
address of the configured interface for relaying packets to the DHCP server. For example, if you configure DHCP relay source
interface as a loopback interface, the DHCP relay uses the configured loopback interface to forward the packets to the DHCP
server using the configured IPv4 or IPv6 address. The source interface can be a VLAN, LAG, physical and loopback interfaces.
● Specify the type of an interface and interface-number that should be used as a DHCP relay source interface.
CONFIGURATION mode
{ip | ipv6} dhcp relay source-interface interface
Following is the sample configuration to configure loopback interface with IPv4 and IPv6 address in CONFIGURATION MODE.
Dell(conf)# interface loopback 1
Dell(conf-if-lo-1)# ip vrf forwarding vrf1
Dell(conf-if-lo-1)# ip address 1.1.1.1/32
Dell(conf-if-lo-1)# ipv6 address 1::1/128
Dell(conf-if-lo-1)# no shutdown
To configure the loopback interface as IPv4 or IPv6 DHCP relay source interface, enter the following commands in the
CONFIGURATION MODE.
Dell(conf)# ip dhcp relay source-interface loopback 1
Dell(conf)# ipv6 dhcp relay source-interface loopback 1
When you configure the above commands in the CONFIGURATION MODE, it will configure the loopback interface as the DHCP
relay source interface for forwarding the DHCP packets from DHCP client to server. When this command is configured in the
CONFIGURATION mode level, it is applied globally. So, all the DHCP packets will be relayed or forwarded through the configured
L3 interface (loopback 1) using the IPv4 (1.1.1.1/32) and IPv6 addresses (1::1/128) of the loopback configuration.
Dynamic Host Configuration Protocol (DHCP)
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