Need Help Understanding Cisco IP NAT Example

Hello Experts,

I am having a difficult time understanding what this Cisco example is saying. I read this article here (http://www.ciscosystems.com/en/US/products/hw/routers/ps274/products_configuration_example09186a0080819289.shtml) and in the example it says:

!--- The access list is used to specify which traffic
!--- is to be translated for the outside Internet.
 

access-list 111 deny ip 10.10.10.0 0.0.0.255 192.168.1.0 0.0.0.255
access-list 111 permit ip any any

Does this mean that any packets that matches access-list 111 that denies 10.10.10.0 (source of main office) to 192.168.1.0 (VPN user) or something? Can someone translate this in a easier way?
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katredrumAsked:
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rvandenbrinkCommented:
the 10.10.10.0 / 24 network is the "inside" network
the 192.168.1.0/24 network is the pool of ip addresses that is assigned to remote users vpn'ing in

so the ACL is saying:
Don't NAT between the VPN clients and the internal network
NAT everything else (ie - NAT all inside traffic destined for the internet)

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katredrumAuthor Commented:
Wonderful translation, I can understand that, but I always thought ACLs are:

deny ip (source) (wildcard) (destination) (wildcard)

In your translation, don't NAT between (destination) then (source), can you please clarify?
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katredrumAuthor Commented:
So if it was a permit as:

access-list 111 permit ip ip 10.10.10.0 0.0.0.255 192.168.1.0 0.0.0.255

then translation would be?:
NAT between the VPN clients and internal network (which it wouldn't work but just for translation)
Deny everything else (implicit deny)
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rvandenbrinkCommented:
In this case, you are not using the ACL to permit or deny traffic to pass on the interface, you are defining what traffic to apply to the NAT operation.

In cisco-speak, you are defining "interesting traffic" for NAT
Since ACLs are evaluated sequentially, you put the deny first.

so you are saying:
DON't NAT between 10.10.10.0/24 and 192.168.1.0/24
DO NAT everything else


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katredrumAuthor Commented:
Sorry one more question. So would it be the same if we flipped the statement as:

access-list 111 deny ip 192.168.1.0 0.0.0.255 10.10.10.0 0.0.0.255 be the same as
access-list 111 deny ip 10.10.10.0  0.0.0.255 192.168.1.0 0.0.0.255?
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katredrumAuthor Commented:
I guess there is no explanation for my last question? Thanks anyway.
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