  The Border Gateway Protocol (BGP) sets up routes between the smaller networks
that make up the Internet. Despite its crucial role, BGP is notoriously
vulnerable to serious problems, including (1) propagation of bogus routing
information due to attacks or misconfigurations, and (2) network instabilities
in the form of persistent routing oscillations. The conditions required to
avoid BGP instabilities are quite delicate. How, then, can we explain the
observed stability of today's Internet in the face of common configuration
errors and attacks? This work explains this phenomenon by first noticing that
almost every observed attack and misconfiguration to date shares a common
characteristic: even when a router announces egregiously bogus information, it
will continue to announce the same bogus information for the duration of its
attack/misconfiguration. We call these the "fixed-route attacks", and show
that, while even simple fixed-route attacks can destabilize a network, the
commercial routing policies used in today's Internet prevent such attacks from
creating instabilities.
