the internal server is always made of servers and clients just like the external one. if you compromise one server you have access to the data transiting there,

the internal server is always made of servers and clients just like the external one. if you compromise one server you have access to the data transiting there, but not the others if you compromise one client you have access to the data this client sends only in particular, very few internal networks enforce L2 security (ie its possible to sniff all data on the same VLAN as you are).