Users Guide

In VxLAN symmetric and asymmetric IRB scenarios, Dell Technologies recommends having the same relay configurations at the
Global and Interface level on the VTEP OS10 devices.
Dell Technologies recommends enabling the DHCPv4 virtual subnet selection and link selection options along with the server
ID override option. Enabling DHCPv4 options without the server ID override option might not work when the DHCPv4 server
renews or releases the client IP address that is based on these options. The server ID override option is supported only on VLAN
or VXLAN interfaces as the virtual-router (virtual router anycast gateway IP) configuration is available only on VLAN or VXLAN
interfaces and the same is used to fill the server ID override option.
Use Case 1: Source-interface CLI link selection and server-override
suboptions
In the following example, the DHCP client is connected on eth 1/1/1.
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 47. 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
System management
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