topic Re: open translated IP from the inside in Network Security

open translated IP from the inside

ronshuster — Mon, 11 Mar 2019 18:08:08 GMT

we have a ASA5500 with 3 interfaces : outside, dmz, inside

we have a number of static nats translating a given public IP to a dmz servers and that all works fine. However for testing purposes, we need to be able to access the public IP from the inside interface.

I tried the following but that did not work:

static (inside,inside) <public_IP> <dmz_IP> netmask 255.255.255.255

what translation is missing to allow users from the inside to access the public ip address?

Re: open translated IP from the inside

Marcin Latosiewicz — Tue, 06 Jul 2010 13:53:57 GMT

I would start with

static (dmz,inside) netmask 255.255.255.255

enable logging on informational level from and test.

After test do "show logg | i IP.address"

Marcin

Re: open translated IP from the inside

Nagaraja Thanthry — Tue, 06 Jul 2010 14:09:49 GMT

Hello,

As Marcin said, you need to configure the static with "static (DMZ,inside) " format. Also, ensure that there is NAT translation between the inside and the DMZ. It could be identity NAT or dynamic PAT.

static (inside,DMZ) netmask

access-list nonat permit ip

nat (inside) 0 access-list nonat

global (dmz) 1 interface

nat (inside) 1 0.0.0.0 0.0.0.0

This will ensure that all traffic from inside (higher security) is going to DMZ with proper NAT translations.

Hope this helps.

Re: open translated IP from the inside

ronshuster — Tue, 06 Jul 2010 14:32:01 GMT

So which one is it?

Marcin says:

static (dmz,inside) netmask 255.255.255.255

Nagaraja says:

static (inside,DMZ) netmask

and what is the logic behind this?

Re: open translated IP from the inside

Marcin Latosiewicz — Tue, 06 Jul 2010 14:34:26 GMT

We're not contadicting each other. 🙂

You need to make sure that servers from DMZ to inside are translated (what I was going for).

But at the same time, it's best to NAT inside users to somethin on DMZ. Be it identity or PAT.

Re: open translated IP from the inside

Nagaraja Thanthry — Tue, 06 Jul 2010 15:11:06 GMT

You need both of them for proper communication between the interfaces i.e. inside and DMZ. As Marcin said, one will ensure that when your inside hosts try to access the public IP of the DMZ server, it gets translated to corresponding DMZ IP. Other one is needed to satisfy the firewall requirement i.e. NAT rules are needed when you go from higher security interface (inside) to a lower security interface (DMZ).

Hope this helps.

Re: open translated IP from the inside

ronshuster — Tue, 06 Jul 2010 15:43:44 GMT

I have added the following 2 lines to the firewall:

static (dmz,inside) 192.168.1.15 netmask 255.255.255.255

The users on the inside are 172.0.0.0\8

static (inside,dmz) 172.0.0.0 172.0.0.0 netmask 255.0.0.0

This is the translation from the outside...it was there before

static (dmz,outside) 192.168.1.15 netmask 255.255.255.255

I am still unable to access the public address from the inside or from the dmz

Re: open translated IP from the inside

Marcin Latosiewicz — Tue, 06 Jul 2010 15:47:44 GMT

What went wrong? Can you please check the logs (informational level)?

Marcin

Re: open translated IP from the inside

Nagaraja Thanthry — Tue, 06 Jul 2010 15:49:35 GMT

Do you have any nonat or identity NAT configurations from DMZ to inside? It would look like:

nat (DMZ) 0 access-list

static (DMZ,inside) 192.168.1.x 192.168.1.x netmask 255.255.255.255

If you have these, that could be the reason you are not able to access. Please modify the configuration so that there is no identity nat from DMZ to inside.

Hope this helps.