Users Guide
Loopback 0 is used as the relay source-interface for the default VRF clients. The server-override option is enabled on the
default VRF.
Configure the DHCP relay agent globally to insert the server ID override suboption (suboption-11) and link selection suboption
(suboption-5) into the relay agent information option of the DHCP packet.
The DHCP client sends a broadcast DHCP request on the network.
The DHCP relay agent inserts a server ID override suboption and link selection suboption to its relay agent information option in
the DHCP packet. The link selection suboption contains the incoming interface IP address, 1.1.1.1. In this case, as the
interface IP address is present, link selection uses the 1.1.1.x subnet. If the interface IP address is not present, the virtual
gateway address is used in VxLAN scenarios. The server-override option carries the virtual anycast gateway IP address. In case
the virtual gateway IP address is not configured, the server-override option does not carry any value.
Table 33. Source-interface values
Field/suboption Value
giaddr (source-interface) 3.1.1.1
link selection (suboption-5) 1.1.1.1
server-override (suboption-11) 1.1.1.254
As the source interface is explicitly configured on the Loopback 0 interface, the relay agent uses that address as the gateway IP
address (giaddr) for messages relayed to the DHCP server, 3.1.1.1.
DHCP Relay Agent
Global config
ip dhcp-relay server-override
ip dhcp-relay link-selection
VRF config for source-interface
ip vrf default
ip dhcp-relay source-interface loopback 0
interface loopback0
no shutdown
ip address 3.1.1.1/32
!
interface virtual-network 100
no shutdown
ip address 1.1.1.1/24
ip helper-address 20.1.1.2
ip virtual-router address 1.1.1.254
!
interface Ethernet 1/1/2
no shutdown
ip address 20.1.1.1/24
DHCP Server
OS10(config)# ip dhcp server
OS10(config-dhcp)# pool dell_1
OS10(config-dhcp-dell_1)# network 1.1.1.0/24
OS10(config-dhcp-dell_1)# range 1.1.1.2 1.1.1.10
OS10(config-dhcp-dell_1)# default-router 1.1.1.254
OS10(config-dhcp-dell_1)# end
OS10#show running-config ip dhcp
!
ip dhcp server
!
ip dhcp pool default
network 1.1.1.0/24
default-router 1.1.1.254
address range 1.1.1.2 1.1.1.10
OS10# show running-configuration route
ip route 1.1.1.0/24 20.1.1.1
ip route 3.1.1.0/24 20.1.1.1
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System management