When using Auto Deploy you have two options for managing the IP addresses of your ESXi hosts: (1) use static reservations in DHCP or (2) use an answer file. I'll go over each of these options.
1. I like to use static DHCP reservations as this eliminates the extra step of having to pre-populate an answer file for each host. With a static IP reservations the DHCP server assigns an IP address based on the host's MAC address, this ensures that each time the host boots the DHCP server will always assign the same IP address. Because the host always gets the same IP address from the DHCP server there is no need to reconfigure the hosts' network using an answer file when the host profile is applied.
Configuring static IP reservations in DHCP is very easy. Simply provide the MAC address of the primary NIC being used for the management network and enter the IP address you want to be assigned. The steps to configure static IP reservations on a Windows DHCP server can be found in the vSphere Installation and Setup Guide.
2. Another approach for configuring IP addresses for your Auto Deployed ESXi hosts is to create an answer file. Answer files are a new feature in host profiles introduced in vSphere 5.0. Where host profiles are used to store configuration parameters that are common to many hosts, answer files store info that is unique for each host, such as IP addresses.
The downside to using answer files is that you must first do an initial deployment of each host in order to manually populate each host's answer file. An example of how to do this is available in the vSphere Installation and Setup Guide. However, once the answer file has been created it will be used to automatically reconfigure the host's network during all future reboots without additional user intervention.
Note that it is possible to preconfigure the answer files using scripts. This can eliminate the need to manually pre-configure each hosts but it does require some scripting skills. Refer to this blog for more information on how to accomplish this.
I tend to prefer using static IP reservations in DHCP, but either approach will work. I know many customers who prefer using answer files as it allows them to maintain their ESXi host IP addresses on their own without having to involve the DHCP administrator each time they deploy new hosts or want to make changes.
