asked on

Selective NAT Rule

I would like to get around the port 25 blocking by my ISP.

At my office, I have an existing NAT rule for private server to a public IP address, on port 25. For the same server I would like to NAT port 25 to 8025, but only for traffic to/from a specific IP address (home). On the home side, I'll have only 25>8025 for all traffic.

It will look like this:
Office Server(25) <> Cisco ASA(8025) <> Internet <> Home FW(8025) <> Home Server(25)
Office Server(25) <> Cisco ASA 5510(25) <> Internet <> Everyone Else(25)

This seemed like a simple matter. But I can’t add the 25>8025 NAT rule because it overlaps the existing 25>25 NAT rule.

Can this be done, or is it simply not possible?

surbabu140977

Cisco do support putting this. I do not have an ASA at my disposal, but I tried putting this into my router and it seem to be taking. Assuming your office server is 172.16.1.1 which translates to 1.1.1.1 in public, here is what I used in my router.

ip nat inside source static tcp 172.16.1.1 25 1.1.1.1 25 extendable
ip nat inside source static tcp 172.16.1.1 25 1.1.1.1 8025 extendable

Best,

surbabu140977

Did you try putting----

static (inside,outside) tcp 1.1.1.1 25 172.16.1.1 25
static (inside,outside) tcp 1.1.1.1 8025 172.16.1.1 25 ???

Is it replacing?

Best,

LimeRidge29

ASKER

No. The second NAT rule conflicts with the first one.
"ERROR: duplicate of existing static"

Right now, I have all port 25 traffic NATing to 8025:
static (inside,outside) tcp interface 8025 172.16.1.1 25 netmask 255.255.255.255

So I can reach my home server, but I can't reach any other public SMTP servers. If my home server public IP addresss is 1.2.3.4, I would like to be able to apply the 25>8025 NAT rule for all traffic to/from 1.2.3.4. For all other traffic, I want to apply a simple 25>25 NAT rule.

ASKER CERTIFIED SOLUTION

surbabu140977

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mikebernhardt

If your ISP is blocking port 25, why are you bothering with the existing rule? But on a router (I don't have an ASA either) I could do this:
ip nat inside source static tcp 1.1.1.1 25 2.2.2.2 25
ip nat inside source static tcp 1.1.1.1 25 3.3.3.3 8025

By allocating an additional public address you may be able to make it work.

LimeRidge29

ASKER

The existing rule is for my office server - there is no port blocking, so it's just a simple PAT. This is looking like it can't be done with the ASA. I may just need to upgrade my home Internet connection to business class.

SOLUTION

mikebernhardt

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LimeRidge29

ASKER

I've requested that this question be closed as follows:

Accepted answer: 0 points for LimeRidge29's comment #a39491069

for the following reason:

Does not provide a definitive answer to the original question.

mikebernhardt

the question was "Can this be done, or is it simply not possible?" We answered the question quite definitively- it's not possible given the user's current capabilities. I will not comment on how to award points- I think both of us said the same thing and it's up to LimeRidge29 to determine whether one answer was more clear or to split points. But it's unfair to simply close the question in my opinion.

LimeRidge29

ASKER

I should not accept my final comment as the solution.

mikebernhardt

Good luck! I think it will be a lot easier if you upgrade.