Cisco Support Community
Community Member

Pix behind Cable Modem/DSL and hosting Mail

If I have a cable modem/DSL box that has a single static on the outside of it, and it does NAT and DHCP, can I host an SMTP server inside a Pix?

Example, outside device is at It delivers DHCP Addresses. The Pix picks up as its outside address. It in turn gives addresses internally, and the SMTP host is at

How would I set the MX record to point to and have the Pix deliver port 25 traffic to

Do you remove NAT on the Pix and use the subnet on both sides?

I get the feeling this can be done with version 6.2(2), but I am having a mental block on how.

Thanks for all assistance in advance.


Re: Pix behind Cable Modem/DSL and hosting Mail

If the cable/dsl box does nat, why are you using a pix? You need a legitimate ip address on the outside of the pix. If you can achieve that:

set up the mx record to point to a host. have a record for that host to be 65.x.x.x.

on the pix:

global (outside) 1 interface

static (inside, outside) tcp interface 25 25 netmask

write an access list that allows smtp from everyone:

... permit tcp any any smtp

apply it to the outside interface.


CreatePlease to create content