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Lan 2 Lan vpn Cisco ASA 5505 with NAT

Posted on 2009-04-05
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Last Modified: 2012-05-06
Hi all

i am currently trying to configure a LAN 2 LAN (site to site) vpn between a cisco ASA 5505 and a cisco 3845 router. I only have access to the ASA.

I usually just use the site to site vpn wizard and it works great but now the other guy (on the 3845) is asking me to enable NAT before the encryption (config will be like this : inside--NAT--cryptomap--L2L--cryptomap--NAT--inside).

I am not quite proficient with this kind of configuration. Can someone help?

Thx in advance

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Question by:inf2300
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cosmicfox earned 500 total points
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You can do this by breaking it down into two steps, first configure your nat rule so lets say your source ip is 192.168.1.x and you need to nat to 10.1.1.x, setup your nat rule according. Then when you setup your site to site the source ip will be your natted ip of 10.1.1.x. The way it works is a nat rule will be kicked off before the ipsec will send the traffic over the tuennl.

Hope this helps, let me know if you need any more information.
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by:inf2300
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So the nat will get executed before it encrypts the traffic?

Thx for the info, I will try that tomorrow
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by:cosmicfox
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Yes nat is done before crypto. here is a link to the order of operation.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080133ddd.shtml
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by:inf2300
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So how should the nat configurations and access-list go?

Lets say these are my different ranges

inside range : 192.168.2.0/24
my public ip : 5.5.5.5

their peer ip : 6.6.6.6
their inside public ip range : 138.11.16.0/24
their inside range : unknown

So if I get this right, the other guy has this setup : (6.6.6.6)router-----(138.11.16.0/24)firewall------(unknown private range)inside

He told me to NAT my subnet first for security reasons...

I understand the principles, just not sure how to apply it...

Usually, I just exempt the 2 protected subnet from the NAT...



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by:inf2300
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nevermind I just figured it out and make it work
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by:inf2300
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thx for your help!!
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