So you are assigning a static IP address through your DHCP server? When you installed the ESXi software did you assign and IP address or let itt obtain an IP address from the DHCP host?
Here are a couple of docs that will help you setting up your network -
http://pubs.vmware.com/vsphere-51/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-511-installation-setup-guide.pdf - the information starts on page 171 -
For more detailed information you might also want to look at http://pubs.vmware.com/vsphere-51/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-511-networking-guide.pdf