  Supernova remnants (SNRs) are the best candidates for galactic cosmic ray
acceleration to relativistic energies via diffusive shock acceleration. The
gamma-ray emission of SNRs can provide direct evidence of leptonic (inverse
Compton and bremsstrahlung) and hadronic (proton-proton interaction and
subsequently pion decay) processes. Puppis A is a ~ 4 kyr old SNR interacting
with interstellar clouds which has been observed in a broad energy band, from
radio to gamma-ray. We performed a morphological and spectral analysis of 14
years of observations with Fermi-LAT telescope in order to study its gamma-ray
emission. We found a clear asymmetry in high-energy brightness between the
eastern and western sides of the remnant, reminiscent to that observed in the
X-ray emission. The eastern side, interacting with a molecular cloud, shows a
spectrum which can be reproduced by a pion decay model. Moreover, we analyzed
two gamma-ray sources located close to the remnant. The hardness of their
spectra suggests that the gamma-ray emission can be due to particles escaping
from the shock of Puppis A.
