ISC-DHCP is an important part of a Custom JumpStart infra-structure.
Complementing the DHCP base configuration here's a sample for X86 clients:
  
...
group {
  class "vendor-classes" {
    match if (
      substring(
        option vendor-class-identifier, 0, 9
      ) = "PXEClient"
    );
  }
  use-host-decl-names on;
  host X86-client-1 {
    hardware ethernet XX:XX:XX:XX:XX:XX;
    fixed-address 192.168.0.218;
    filename "01XXXXXXXXXXXX";
  } 
  host X86-client-2 {
    hardware ethernet YY:YY:YY:YY:YY:YY;
    fixed-address 192.168.0.219;
    filename "01XXXXXXXXXXXX";
  } 
  # and so on ...
   
  # JumpStart server (BootSrvA) where to get filename (BootFile)
  next-server 192.168.0.10;
  # The magic below (on a single line) avoids bug PXE-E74
  # The highlighted portion means "Network boot" ... "Prompt"
  option vendor-encapsulated-options 09:0F:80:00:0C:4E:65:74:77:6F:72:6B:20:62:6F:6F:74:0A:07:00:50:72:6F:6D:70:74:06:01:02:08:03:80:00:00:47:04:80:00:00:00:FF;
} 
    
Note: There are many differences in SPARC Custom JumpStart DHCP.