topic What is the best way to bypass NAT on FWSM in Network Security

What is the best way to bypass NAT on FWSM

rrockliff — Mon, 11 Mar 2019 21:13:31 GMT

Hi All

I want to setup my FWSM so that the outside networks can communicate with the inside networks on their real ip address and visa versa. This is not an Internet facing Firewall and only being used to filter traffic between some secure networks, all of the users, domain controllers etc will sit on the outside, the mission critical devices will sit on the inside networks

Should i disable NAT control

or create nat rules similar to bellow using identity nat

nat (inside) 0 10.1.1.0 255.255.255.0

and

nat (outside) 0 10.1.20 255.255.255.0

Thanks for any assistance

Cheers

Richard

What is the best way to bypass NAT on FWSM

varrao — Thu, 18 Aug 2011 02:20:47 GMT

Hi,

You can do both, eith disable nat-control and just allow the traffic from outside to inside through ACL's, or use nat exempt, something like this:

Lets say your source network on outside is 10.0.0.0/8 and inside is 20.1.0.0/16, then

access-list nonat permit ip 10.0.0.0 255.0.0.0 20.1.0.0 255.255.0.0

nat (outside) 0 access-list nonat

This would translate the ip into themselves, and is the correct way to do it.

Hope this helps.

Thanks,

Varun

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What is the best way to bypass NAT on FWSM

rrockliff — Thu, 18 Aug 2011 02:29:05 GMT

Thanks for the reply,

What is the main difference between using identity nat and disabling nat control

Is there a benefit to keeping nat control on and using the nat (outside) 0 method

What is the best way to bypass NAT on FWSM

varrao — Thu, 18 Aug 2011 02:34:13 GMT

Well there is no difference, enabling nat-control and using identity nat is only helpful if you want to nat all traffic but some specific traffic or subnet need not be natted, so you use nat exempt.

Moreover nat exempt is helppful because, you can specify the destination as well, along with the source, so as in my example, if the same subnet is going to 30.0.0.0, it would need natting, so it makes things a bit flexible.

Hope this helps

Thanks,

Varun