I have the following network scenario:
An Internal Mail server that forward the mail messages to an external sendmail server that send/receive the mails from Internet.
Between the two mails servers starting from the inside, there are a L3Switch that act like bridge among the internal networks subnets 172.16.0.0/22 where is connected the internal mail server .161.
The L3Switch is connected to the first Pix on the inside interface, and it is connected to the second Pix inside interface by its Dmz interface.The second pix has connected on the outside interface the ISP router, and on its DMZ the sendmail server that has a public ip 126.96.36.199/29.
My question is:
From a security point of view, how is important that the internal and external mail server do not has routing informations about the external and internal networks ?I have configured the second pix to perform a port redirection in this way:
static (dmz,inside) tcp 172.16.243.1 smtp 188.8.131.52 smtp netmask 255.255.255.255
The internal mail server forward the mail to 172.16.243.1 the pix apply the static, perform the port redirection to 184.108.40.206.
Than I have added also:
static (dmz,inside) 172.26.243.1 220.127.116.11 netmask 255.255.255.255
In this way the pix perform the outside nat so the source address is changed from 18.104.22.168 to 172.26.243.1,so I have configured on the external mail server the 172.26.243.1 instead of the real ip.