topic Re: ASA NAT in Network Security

ASA NAT

Waterbird — Fri, 21 Feb 2020 16:32:32 GMT

Please explain this configuration. What kind of NAT is it using and how can I learn how to configure it?

nat(any,outside) source static OBJECT-GROUP-1 OBJECT-GROUP-1 destination static OBJECT-GROUP-2 OBJECT-GROUP-2 no-proxy-arp route-lookup

nat(any,outside) after-auto source dynamic any interface

Re: ASA NAT

balaji.bandi — Wed, 05 Dec 2018 20:43:09 GMT

There is a good document to understand please refer below document :

https://www.netcraftsmen.com/nat-configuration-on-asa-8-4-part-2/

https://www.cisco.com/c/en/us/td/docs/security/asa/asa84/configuration/guide/asa_84_cli_config/nat_overview.html#wp1118157

Re: ASA NAT

Karsten Iwen — Wed, 05 Dec 2018 20:43:01 GMT

When going out of the outside interface from OBJECT-GROUP-1 to OBJECT-GROUP-2, you don't do any NAT. For the rest of the traffic going out of interface outside you PAT (or hide-nat/masquerade) the source to the IP of the outside interface.

For learning more, Jounis intro is still a good read:

https://community.cisco.com/t5/security-documents/asa-nat-8-3-nat-operation-and-configuration-format-cli/ta-p/3143050

Re: ASA NAT

mkazam001 — Wed, 05 Dec 2018 22:36:31 GMT

the asa has 3 main categories of nat - manual nat, object nat (auto nat), and manual nat after auto

these are actually applied in sequential order like an acl

sh nat - will show the order of the rules

sh run nat - to see the actual nat config

this is using static nat - this entry is also known as nat exemption & is often used for vpn traffic

for traffic using any ingress interface & egressing the outside interface - this nat rule will apply

obj-grp 1 has a static mapping to itself only when the dest is obj-grp 2

cisco rec to use no-proxy-arp & route-lookup - so asa int wont send arp for next hop & will use route table for traffic

regards, mk

Re: ASA NAT

Waterbird — Thu, 06 Dec 2018 15:11:38 GMT

This document you provided a link for was very helpful in providing an overview of the new NAT. Exactly what I was searching for.

This configuration I provided is for a VPN tunnel, so it seems the first statement is identity NAT, which is a variation of Twice NAT / Manual NAT, in Section 1. It's purpose appears to be to not do NAT for the traffic from the first object group to the second object group or backwards, i.e. "no NAT for either source or destination networks".

The second NAT statement appears to be dynamic PAT, implemented using Twice NAT / Manual NAT, in Section 3, and must serve to NAT traffic that is not contained in the object groups.