  A significant fraction of Kepler systems are closely-packed, largely coplanar
and circular. We study the stability of a 6-planet system, Kepler-11, to gain
insights on the dynamics and formation history of such systems. Using a
technique called `frequency maps' as fast indicators for long-term stability,
we explore the stability of Kepler-11 system by analyzing the neighbourhood
space around its orbital parameters. Frequency maps provide a visual
representation of chaos and stability, and their dependence on orbital
parameters. We find that the current system is stable, but lies within a few
percent of several dynamically dangerous 2-body mean-motion resonances. Planet
eccentricities are restricted below a small value, $\sim 0.04$, for long-term
stability, but planet masses can be more than twice their reported values
(thus, allowing for the possibility of mass-loss by past photoevaporation).
Based on our frequency maps, we speculate on the origin for instability in
closely-packed systems. We then proceed to investigate how the system can have
been assembled. The stability constraints on Kepler-11 (mainly, eccentricity
constraints) suggest that if the system were assembled in-situ, a dissipation
mechanism must have been at work to neutralize eccentricity excitation. On the
other hand, if migration was responsible for assembling the planets, there has
to be little differential migration among the planets, to avoid them either
getting trapped into mean motion resonances, or crashing into each other.
