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Embedded Computational Elements in Extensible Routers (Thesis)

Report ID:
September 2002
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The demand to extend the set of services, such as network address
translation, firewalls, proxies, and virtual private networks, that are
supported by Internet-connected devices represents an opportunity to extend
the traditional domain of Internet routers beyond simple packet forwarding.
An important characteristic is the ability for end-users to install custom
services on their routers. Routers with this characteristic are extensible.

Due to their critical position in the Internet topology, routers must be
robust---when presented with unanticipated workloads, they must allocate
their resources across the services they support according to
administrator-established policies to ensure that each service gets the
resources it needs.

By their nature, hardware-based routers with physically isolated control and
data planes are robust but not readily extensible without a redesign while
software-based routers may be extensible but are not robust without extensive
regression testing; it is difficult to be simultaneously robust and
extensible. The most common approach for router vendors is to favor
robustness, and support new services on a case-by-case basis. Allowing the
end-user to develop and install router services dooms this case-by-case
approach to extensibility.

Emerging hardware in the form of intelligent, multi-port line cards that have
their own embedded processing capabilities, based on either microprocessors
or network processors, suggests that one can build cost-effective PC-based
routers that lie in the design space between purely hardware- and
software-based. However, the increased diversity of configurations makes
both extensibility and robustness challenging. We do not want to require
developers to re-implement services for every possible hardware
configuration. How do we map the desired services onto the hardware to
preserve robustness?

In this thesis we demonstrate that one can build a router from PC-based
components, including programmable line cards, that is simultaneously
extensible and robust. To show this, we describe an architecture, called
VERA, that supports extensibility through an explicit interface and
robustness through isolation of services; we present techniques to implement
this architecture on a PC-based router; and we characterize and analyze the
problem of mapping the services to the various, heterogeneous processors
comprising the router to preserve robustness.

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