Who Invented the Firewall?

The list of firewall 'inventors' is large and controversial. Who's really the firewall's daddy?

JANUARY 15, 2008 | 5:45 PM By Kelly Jackson Higgins Senior Editor, Dark Reading Nir Zuk says he developed the technology used in all firewalls today. David Pensak claims to have built the first commercially successful firewall. Marcus Ranum says his own reputation as inventor of the firewall is "marketing BS," and that David Presotto is the man. (See Ranum's Wild Security Ride.) William Cheswick and Steven Bellovin, who literally wrote the book on firewalls in 1994 while at AT&T Bell Labs, say they didn't invent the firewall, either -- they built a circuit-level gateway and packet filtering technology. But all of these security experts -- as well as Jeff Mogul, Paul Vixie, Brian Reid, Fred Avolio, and Brent Chapman, and others -- were associated in some way with the roots of firewall technology. Several of them have been called the father of the firewall, but most experts agree that there's not just one biological father of the technology. "There were lots of people involved in it... The idea was floating around," Ranum says. John Pescatore, vice president and distinguished analyst at Gartner, explains it this way: "Cheswick and Bellovin were the fathers of the network firewall concept: Use packet filtering to deny all except that what is specifically allowed. Ranum was the father of the first firewall 'product' -- DEC SEAL, the open source [firewall], and the TIS Gauntlet," Pescatore says. "And Presotto [and his colleagues] added the stateful inspection concept. Zuk was the father of the stateful firewall product at Check Point, and later pushed the appliance approach at NetScreen, so I would call him the father of the firewall appliance," Pescatore says. The firewall's history has been well-documented, for sure, but it's tough to pinpoint just which stage of the firewall was zero day. Most security experts trace the firewall's roots, back to work done at Digital Equipment Corp. in the late 1980s by Jeff Mogul, Brian Reid, and Paul Vixie, starting with the gatekeeper.dec.com gateway, as well as to Mogul's "screend" technology. DEC SEAL, which was shipped in 1992, was the first commercial firewall and included proxies developed by Ranum. "DEC SEAL was interesting because it had a part number and a manual and a corporation behind it," Ranum says. During the late '80s and early '90s Cheswick, Bellovin, and company were also working on their version of the technology. "But they were building a different technology [to solve] a different problem. AT&T didn't want anything to get out," recalls Avolio, now an information assurance analyst for Johns Hopkins University's Applied Physics Lab. He says the teams from DEC and AT&T eventually did collaborate some on their research. Meanwhile, Zuk, who helped build Check Point's firewall technology, isn't shy about taking credit for the first commercial firewall. "There is only one firewall technology in the world today -- the one that I invented. All the other guys'... work was purely academic and on paper," says Zuk, CTO of Palo Alto Networks, which sells application-aware firewalls. "Check Point's firewall was the first usable firewall that worked," he says. (See Firewalls Ready for Evolutionary Shift and Startup Puts New Spin on Firewalls.) Then why have other security experts also been called fathers of the firewall? "Success has a lot of parents," he says. Pensak, CTO at V.i. Labs, says there are several players besides himself who had a part in the evolution of the firewall. "Each of us had a role to play. The guys I would consider fathers on the technology end of it are Marcus Ranum, Fred Avolio," and others, he says. Interestingly, not all of the firewall's "fathers" are big fans of the firewall anymore. Cheswick, lead member of the technical staff at AT&T Research, says he hasn't personally used a firewall since the 1990s: "They are an economic solution to weak host security. I want to see stronger host security," he says. Even so, Cheswick says the firewall still has a place -- but as "just another network element." "The firewall as Bill and I described it in 1994 in our book is obsolete," says Bellovin, now a professor of computer science at Columbia University. Having a guard at the front door today when there are thousands of backdoors into the network just doesn't fly now, he notes. "I'm not saying get rid of it at the door. It provides a low grade of access control for low-value resources. But the real access control [should be] at the host."