Software-based routers have always played a role in the Internet, and are becoming increasingly important in data centers due to the convergence of video, mobile, and cloud services. Data traffic no longer moves simply from the subscriber into the network and then out again. Instead, most of the traffic is located inside the data center between various application servers within the network.
All this traffic can be routed easily using software-based routers running on commodity PC hardware. Such a router looks like just another server in the data center, and most of the time it is implemented using open-source software solutions. The availability of the source code and the right to modify it enables the unlimited tuning and optimization of the network traffic.
This is a short list of some open-source routing platforms available:
Quagga is a routing software suite, providing implementations of OSPF, RIP and BGP protocols. Quagga runs on most Unix platforms such as FreeBSD, Linux, Solaris and NetBSD. Quagga is a fork of now defunct GNU Zebra project. The software is released under GPL license.
OpenBGPD is a free implementation of the BGP protocol for BSD platforms. It is released under BSD license and is part of OpenBSD project. Ports to Linux systems are also available in several Linux distributions. OpenBGPD is also included in various router/firewall systems such as pfSense.
RCP100 is a new routing software suite implementing RIP and OSPF. It is the single router in this list featuring a CISCO-like command line interface and access control list support. The software is published under GPL license and runs on Linux platforms.
BIRD is a routing software suit implementing RIP, OSPF and BGP. BIRD was developed as a school project at Faculty of Math and Physics, Charles University Prague and it is published under GPL license.
XORP is a routing software suite originally designed at the International Computer Science Institute in Berkeley, California. XORP supports RIP, OSPF and BGP. The software is published under GPL license and runs on Linux and BSD platforms.