Is it possible to forward DNS requests addressed to a PIX inside interface out to ISP's DNS?
Officially, PIX is not designed to do so. But we can make it work by using following commands-
Suppose that ISPs DNS server IP is 18.104.22.168 and PIX inside interface IP is 22.214.171.124. In this case, try following commands:
static (outside,inside) udp interface 53 126.96.36.199 53
Now all the UDP port 53 requests, which are DNS requests, when directed to PIX's inside interface IP, PIX will redirect them to udp (53) on the ISP's DNS server.
Hope this works for you.