  We report the lowest frequency measurements of gamma-ray burst (GRB) 171205A
with the upgraded Giant Metrewave Radio Telescope (uGMRT) covering a frequency
range from 250--1450 MHz and a period of $4-937$ days. It is the first GRB
afterglow detected at 250--500 MHz frequency range and the second brightest GRB
detected with the uGMRT. Even though the GRB is observed for nearly 1000 days,
there is no evidence of transition to non-relativistic regime. We also analyse
the archival ${\it Chandra}$ X-ray data on day $\sim 70$ and day $\sim 200$. We
also find no evidence of a jet break from the analysis of combined data. We fit
synchrotron afterglow emission arising from a relativistic, isotropic,
self-similar deceleration as well as from a shock-breakout of wide-angle
cocoon. Our data also allow us to discern the nature and the density of the
circumburst medium. We find that the density profile deviates from a standard
constant density medium and suggests that the GRB exploded in a stratified wind
like medium. Our analysis shows that the lowest frequency measurements covering
the absorbed part of the light curves are critical to unravel the GRB
environment. Our data combined with other published measurements indicate that
the radio afterglow has contribution from two components: a weak, possibly
slightly off-axis jet and a surrounding wider cocoon, consistent with the
results of Izzo et al. (2019). The cocoon emission likely dominates at early
epochs, whereas the jet starts to dominate at later epochs, resulting in
flatter radio lightcurves.
