We present in detail the propagation of an IP shock observed by multiple spacecraft in the solar wind and by INTERBALL (IB) in the magnetosheath (hereafter MSH). Our investigation brings an evidence that the observed IP shock slightly decelerates in the MSH contrary to gasdynamic prediction. This result motivates a statistical study of a small number of similar shocks observed in the solar wind and in the MSH that confirmed the case study result. Moreover, we model the interaction of IP shocks with the magnetosphere using an MHD model and show that the observation of shock deceleration agrees with the model prediction. The MHD model suggests that the speed of the shock front propagation in the MSH decreases from the bow shock toward the magnetopause and the front of the IP shock deforms. However, the experimental data are not sufficient to undoubtedly confirm this trend.