Configuring DHCP

Introduction

Each virtual machine network has a corresponding VLAN (or VXLAN with NSX). 

For private, external and public networks, Abiquo uses an ISC DHCP server to manage VLANs (or VXLANs). Abiquo recommends one DHCP server per physical datacenter registered in remote services. Additional DHCP servers may be incorporated in network virtualization solutions. The types of DHCP server configuration are as follows: 

• Remote services DHCP server supplied with Abiquo or other compatible server
  
  • Configure datacenter DHCP as described below
    
    • For example, if you have many virtual machines in a datacenter, you might need a separate relay server to manage VLANs for the DHCP server
  • Add the DHCP service to Abiquo when creating or editing a datacenter
    
• DHCP server incorporated in an integrated network virtualization system
  
  • In an Abiquo datacenter, create a logical device that will enable Abiquo to connect via the API of the network virtualization system to its DHCP server. See Create SDN devices.
  • If the network virtualization system DHCP server is not available, Abiquo will fall back to the datacenter remote services DHCP server
    

For unmanaged networks, Abiquo does not use a DCHP server. So if your platform will only use unmanaged networks, you do not need to configure a DHCP server. However, you must provide the network addresses to the virtual machines outside of Abiquo.

To display the version of DHCP used by Abiquo, run the following command on the Abiquo remote services :

# /usr/sbin/dhcpd --version
isc-dhcpd-4.1.1-P1

Abiquo uses the DHCP server to: 

• Manage the VLANs (or VXLANS), serving IP addresses to virtual machines
• Serve static routes to virtual machines using the DHCP option
• Serve information from the Chef integration using the vendor encapsulated options
  
  • The Chef integration is not available with NSX

How Abiquo Uses DHCP

The connections in DHCP are as follows:

1. When you deploy a virtual machine, Abiquo (Remotes Services) supplies the network settings for the new VM to the DHCP Server.
2. When the new virtual machine powers on, it broadcasts a DHCP request for network configuration.
3. The hypervisor passes the DHCP request through a VLAN to the DHCP server.
4. The DHCP server broadcasts a lease with the network configuration for the virtual machine over the same VLAN

DHCP Configurations

When configuring DHCP for a datacenter using the remote services, the possible DHCP configurations are:

The first configuration (DHCP Server only) is recommended only for test environments or small environments that will not be scaled up. The configuration with the DHCP relay server is recommended by Abiquo because it easy to set up and troubleshoot and it also scales well. 

DHCP Server

The DHCP Server listens to all the VLANs. Abiquo recommends that you use a separate DHCP Server (not the Remote Services DHCP Service) in this configuration.

DHCP Server with DHCP Relay

The DHCP relay server listens to all the VLANs and forwards the DHCP requests to the DHCP Server.

DHCP Server with multiple DHCP Relays

Multiple DHCP relay servers allow you to create large networks in a hierarchical forwarding structure.

DHCP Installation Guide

The DHCP Relay Server (or DHCP Server if no relays are used) must be able to listen to VLANs. So it must be a separate physical machine or specially configured virtual machine.
If you wish to use a virtual machine, follow one of these configuration guides to prepare the virtual machine:

• VMware ESXi (see How to configure an ESXi host to support VLAN tagging); or
• Red Hat KVM

Then continue with the appropriate install section for your configuration

Install DHCP Server

1. Install CentOS

2. Install a separate DHCPD server

   yum install dhcpd
   

3. Do the steps in Configuring a DHCP Server

DHCP Server with DHCP Relay

In this configuration you can use the DHCP Server on the Abiquo Remote Services machine. Or you can install a separate DHCPD server.

There are two ways to install the DHCP Relay Server: Abiquo ISO and manual install.

• Abiquo ISO: see Automatically Configuring One DHCP Relay Server.
• Manual Install: see Manually Configuring One DHCP Relay Server

DHCP Server with Multiple DHCP Relays

In this configuration you can use the DHCP Server on the Abiquo Remote Services machine. Or you can install a separate DHCPD server.
See Manually Configuring Multiple DHCP Relay Servers.

• By default, the manual configuration is for multiple networks with separate VLAN tags
• There are a multitude of possible network configurations, so Abiquo does not recommend any specific configuration