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PIX DMZ Internet access

Posted on 2008-06-10
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Last Modified: 2013-11-16
I have a Cisco PIX 515 with a dmz interface enabled. The pc I have put in the dmz can get to the internal network through an access list, but is unable to get to the internet. Below is my DMZ config.

access-list dmz extended permit ip any any

static (dmz,inside) 10.3.0.0 10.3.0.0 netmask 255.255.255.0
static (inside,dmz) 10.0.0.0 10.0.0.0 netmask 255.0.0.0
static (dmz,outside) 207.136.182.4 10.3.0.4 netmask 255.255.255.255 dns
static (dmz,outside) 207.136.182.3 10.3.0.3 netmask 255.255.255.255 dns
static (dmz,outside) 207.136.182.30 10.3.0.5 netmask 255.255.255.255
static (dmz,outside) 207.136.182.7 10.3.0.6 netmask 255.255.255.255
static (dmz,outside) 207.136.182.8 10.3.0.7 netmask 255.255.255.255
access-group outside in interface outside
access-group dmz in interface dmz
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Question by:dtadmin
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by:batry_boy
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What do your "nat" and "global" statements look like?
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by:dtadmin
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global (outside) 1 interface
nat (inside) 0 access-list nonat-vpn
nat (inside) 1 0.0.0.0 0.0.0.0
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by:Voltz-dk
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nat (dmz) 1 0 0
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by:dtadmin
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what exactlly is nat (dmz) 1 0 0 telling me?
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by:Voltz-dk
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It says that all access from DMZ when going "outbound" (less secure interface), should be NATed to the global pool on that interface with id 1.

In this case any traffic from DMZ that goes to Internet will be PATed into the PIX outside IP. (Same as is done for traffic from inside).
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by:Voltz-dk
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Well, since you have statics it's not really true that it's ANY traffic.  Cuz the statics have precedense, and thus those will not use the dynamic NAT.
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raptorjb007 earned 500 total points
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Voltz-dl is correct.

Try adding

nat (dmz) 1 0.0.0.0 0.0.0.0

This command will configure your Pix to apply PAT or "NAT overload" to the DMZ VLAN, it is the counterpart to the "nat (inside) 1 0.0.0.0 0.0.0.0" command you already have configured for the inside vlan. Without a the nat command applied to the dmz vlan any device without a static translation will be unable to access the internet as it cannot be translated to an internet address.

Basically, with the "nat(dmz) 1 0 0" command applied, any device on your DMZ VLAN without a static translation will utilize the outside interface's IP address to access the internet.
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