different ip answers

[nnmmss]

hi

i ping and ip address of server which i am quite sure that it exists but some time other ip address answer to it, and some times itself answers. how could this happen that another ip answer to another ip address

for example i pinged
ping 217.x.x.x
reply from 172.y.y.y
reply from 172.y.y.y
reply from 172.y.y.y



but some times i will get the true answer
reply from 217.x.x.x
reply from 217.x.x.x
reply from 217.x.x.x

it is appreciated for any idea of the reasons

Thank you