This article describes how to configure DHCP option 40 on an SRX device.
According to RFC2132, “DHCP Options and BOOTP Vendor Extensions,” option 40 is the Network Information Service Domain Option. It specifies the name of the client’s NIS  domain. The domain is formatted as a character string consisting of characters from the Network Virtual Terminal (NVT) ASCII character set. Its minimum length is 1.
You can configure DHCP option 40 on an SRX device as shown in the example below:
root#set system services dhcp option 40 string "domain.tld"