Dell SmartFabric OS10 User Guide Release 10.5.3

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Use Case 1: Source-interface CLI link selection and server-override suboptions

NOTE: Configure at least one interface to match one of the configured network pools. An interface matches a network pool when its IP address is included in the subnet defined for that network pool. For example, an interface with IP address 1.1.1.1/24 matches a pool configured with network 1.1.1.0/24. For the DHCP server to process DHCP discovery packets, you must configure the IP address pool for all the interfaces on which DHCP packets are received. Also, these interfaces must be connected to the DHCP server. This configuration is required even if the IP addresses are not leased to any DHCP client in the subnet directly connected to the DHCP server.

In the following example, the DHCP client is connected on eth 1/1/1:

dhcp-server-override-suboption

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 1. Source-interface valuesSource-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.