Walker & Dunlop Inc., of Bethesda, a commercial real estate finance company with a primary focus on multifamily lending, announced Tuesday that its loan servicing portfolio has surpassed $40 billion. The portfolio, comprised of over 4,300 commercial loans from across the United States, has an average loan term of over 10 years. The mortgage servicing rights related to this portfolio had a fair value of $432 million at June 30. Walker & Dunlop’s servicing portfolio has grown 473 percent since the end of 2008. Since then, Walker & Dunlop has acquired Column Guaranteed LLC and CWCapital LLC. Walker & Dunlop ended 2013 as the eighth-largest commercial loan servicer in the country, according to the Mortgage Bankers Association.