Is it recommended to use NAT between servers on different layers divided by the internal firewall. For e.g. a segment of firewall is connected to web servers and another segment to DB servers. Is there any advantage of NAT'ing the destination server IPs (to hide the actual ips from the web server segment while connecting to DB).
Also, please let me know if there any DISadvantages of doing so such as performance, uneasy troubleshooting etc.
Hiding the IPs from the two internal segments would depend on your company's security policy. It depends on a number of factors tough. E.g. you have two contractors managing the two different segements, hiding the internal IPs could increase security through the 'security through obscuring' model :) but this is not always the case. However this will increase complications while troubleshooting problems etc.