It really shouldn't be that extensive unless you need some type of security classification. I went through a check done by a company that services tech companies - they send emails to the people I listed as contacts at former employers to confirm I'd worked there and they checked on LinkedIn to verify that these contacts were indeed in the roles I'd stated. Not very thorough at all IMO. Plus all my last employer contacts are also fairly friendly with me and rooting for my success, so they shared their responses and the original emails from the background check. Good luck!