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How to Configure DHCP in an IP Clos Network

 

Requirements

Configure DHCP on the following devices that you configured in the How to Configure an IP Clos Fabric for a Campus Network configuration example. This configuration example uses the following device:

  • An EX4600 switch running Junos OS Release 20.2R3 as a DCHP server. The DHCP server may be an external device in your network.

Overview

Use this section to configure DHCP on the network. To avoid flooding the network with DHCP discover packets, configure DHCP on an interface in a VRF routing instance. Both distribution devices are configured with EVPN multihoming (also called ESI-LAG) to act as a DHCP relay to a Layer 3 reachable external DHCP server. This provides redundant connectivity to maintain DHCP services if one of the distribution devices fail. The link between the server and the distribution layer is an ESI. shows the virtual network topology with a DHCP server. Figure 1 shows the virtual network topology with a DHCP server.

Figure 1: Overlay Virtual Network Topology with a DHCP Server
Overlay Virtual Network
Topology with a DHCP Server

Configuration

CLI Quick Configuration

DHCP Relay Configuration for Access Switches.

Step-by-Step Procedure

  1. On the access switch, configure DHCP Relay.
  2. On the access switch, verify that the route to the DHCP server is reachable via an EVPN type 5 route.
  3. On the access switch, configure VRF support to advertise EVPN type 5 routes to the distribution layer.
  4. On the distribution devices, configure an ESI-LAG interface between the distribution devices and the DHCP server.

    Distribution 1

    Distribution 2

  5. Finally, we configure the EX4600 switch to act as the DHCP server.
  6. On the EX4600 switch acting as the DHCP server, verify that the DHCP clients are successfully being assigned IP addresses.