An Open Source Platform for Designing Programmable Routers

Atanu Ghosh
International Computer Science Institute Center for Internet Research
atanu@icir.org

In the past computers were sold with proprietary operating systems
provided by the manufacturer. A computer was not selected solely on
the performance characteristics of the hardware but also on the
supplied operating system. Maintaining software to run on the various
operating systems was time consuming and expensive each operating
system would provide a different way of performing the same task. When
the time came to buy new computers the pragmatic choice was to buy
whatever had been bought before. If a new manufacturer built a
computer that outperformed all the existing competition it would be
difficult to break into the market as the existing customer software
would have to be modified to run on the new computer. The new
manufacturer would also have to develop a new operating system to run
on the new computer which could take a prohibitive time to
develop. Generally, in the past a small number of computer companies
existed with their proprietary operating systems and innovation was
held at bay by these few companies. A change occurred when the UNIX
operating systems came onto the scene, this was an operating system
that was not tied to any specific hardware. Today buying a computer is
much easier than it was in the past, choose a computer that meets the
required price and performance criteria and then install your
favourite operating system. Every computer in a rack can be from a
different manufacturer but running the same operating system and
application software. Not being tied to a single vendor has made life
easier for the consumer and has provided an incentive for computer
manufactures to innovate as well as allowing new manufacturers into
the market. Even in the field of consumer electronics such as Sony's
Playstation 3, Sony have provided a mechanism for the consumer to
install and run her own operating system.

Unfortunately router vendors are still living in this proprietary
past, routers are totally closed systems with all the problems that
afflicted computers of the past. Router vendors sell proprietary
hardware and software solutions. Most routing protocols are open and
therefore routers from different vendors should interoperate, although
there is a tendency for customers to choose routers from a single
vendor as the configuration mechanism for each vendor is
different. Routers tend to have CPUs that are generations behind what
is readily available in the market as well as being equipped with
ridiculously small amounts of memory. It is not possible to modify the
code that is running on a router, the only way to get change is to
convince the router vendor to make the change, this current model
stifles research and innovation. XORP the eXtensible Open Router
Platform aims to change the proprietary nature of routers. XORP allows
a PC to be used as a router. All the XORP code is open source so it is
possible to modify and add to the existing code base, allowing
research and innovation. XORP supports most unicast and multicast
routing protocols.

XORP has a rich set of libraries and an IPC mechanism to aid in the
writing of routing protocols. One very useful feature of XORP is that
a new protocol can be introduced to the system by providing a
configuration file called a template file and the application binary,
this is all that is required for the new protocol to be configured by
the command line interface. Introducing a new protocol requires zero
changes to any of the existing parts of the system. The simplicity of
adding a new protocol will make is easier for third parties to provide
protocols. We also expect to enable a new type of application the
router application. The router application will be able to use all the
facilities available to a routing protocol.

A programmable router can mean many things but it would seem a
fundamental requirement should be the ability to run programs on the
router. Rather than to try and define a narrow API to program a router
it would seem that the more flexible way forward is to use the rich
set of libraries that XORP provides today to build the extensible
services of tomorrow.