DMZ security

[dondon]

Does anyone know if firewall appliances usually protect its 
LAN port the same as its DMZ port?  

On my Sonicwall I can set port blocking for PCs on both the 
LAN and DMZ port.  If I block traffic to all ports for DMZ 
PCs, is the DMZ essentially the same as the LAN?  Or would 
it be not as safe as the LAN?

thanks,
Andy