Fair enough, but those have mostly served as SOHO firewalls or home gateways. Besides, mostly it's OPenBSD. However, it's only in recent years that more robust and scalable open source implementations of routing protocols have shown up. In my opinion, it's taken way too long : enterprise-class protocol stacks running on distributed Linux or xBSD farms should have conquered low to mid range routing market by now. As a strategist, I think the real barrier to entry is not even the routing protocols per se: it's IOS user interface, i.e. Cisco CLI. It's a lot easier for open sourcers to make a GPL version of GateD than keep up with Cisco CLI with all of its quirks and bugs.