Mapping outbound traffic to external IP.

Unanswered Question
Feb 5th, 2007

I have couple of external IP addresses x.x.x.61 and x.x.x.69. I use the x.x.x.69 for NAT. My mail server (192.168.y.20:25) sits behind the firewall and is mapped to the external address x.x.x.61:25. There is no issue with incomming mail. The problem is that when mail is sent out the message appears as comming from x.x.x.69:25 and not from x.x.x.61:25. Some providers (e.g. Comcast) reject the mail based on the fact that the reverse look up does not match.

Is there a way to setup IOS to map outgoing traffic from 192.168.y.20:25 to x.x.x.61:25?

I have this problem too.
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Jon Marshall Mon, 02/05/2007 - 12:31



ip nat inside source static tcp 192.168.y.20 25 x.x.x.61 25 extendable.

Just out if interest is it IOS you want to do this in or on the firewall ?

If the firewall is a pix then

static (inside,outside) tcp x.x.x.61 25 192.168.y.20 25 netmask



bmvportland Mon, 02/05/2007 - 17:17

Thanks for your quick reply.

I already have the "ip nat inside source...." command. The inbound traffic is routed just fine. It is the outbound traffic that keeps going out as x.x.x.69:25 since the x.x.x.69 is the external NAT IP. What I am looking for is to map the internal 192.168.y.20:25 to x.x.x.61:25

Fernando_Meza Mon, 02/05/2007 - 15:46

Hi ..

If you are using a PIX, then you need to use static NAT instead of port forwarding meaning that you need to use.

static (inside,outside) public_IP Private_IP netmask

I hope it helps .. please rate if it does !!!


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