| Abstract | Many applications can use multipath routing to improvereliability or throughput, and many multipath routing pro-
tocols exist. Despite this diversity of mechanisms and
applications, no common interface exists to allow an ap-
plication to select these paths. This paper presents a de-
sign for such a common interface, called path bits. Path
bits are a small string of opaque, semantic-free bits in a
packet header; these bits have a simple property: changing
a packet’s path bits should, with high probability, result in
the packet taking a different path to the destination. This
paper presents the design of path bits and demonstrates
that they are simple enough to be easily implemented in
both hardware and software and expressive enough to sup-
port a variety of applications that can benefit from mul-
tipath routing. We present both hardware and software
implementations of multipath routing protocols that im-
plement the path bits abstraction, as well as implementa-
tions of applications that can use this abstraction with only
small modifications.
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