RE: Basic NAT / Firewall Question

["David Gillett" <gillettdavid () fhda edu>]

  This is almost certainly up to the firewall admin, how much
the firewall filters and how much it forwards to the NATted 
destination.

  A very basic question is:  Is the firewall doing port-forwarding
(traffic to port ZZ gets translated and forwarded to the server), 
or static NATting (non-filtered(!) traffic for public address x.x.x.x 
gets translated and forwarded to private address y.y.y.y)?

  Also open is what the firewall does with a filtered port --
does it silently drop the traffic, or respond via ICMP and, 
if the latter, does it provide the *same* response that a
blocked port at the host does?  (Probably not, since the
source address will be of the firewall rather than the NATted
destination....)  Some firewall models offer the admin more 
choice in this regard than others.

David Gillett


> -----Original Message-----
> From: thatch [mailto:leethatcher () gmail com] 
> Sent: Friday, August 18, 2006 10:29 AM
> To: security-basics () securityfocus com
> Subject: Basic NAT / Firewall Question
>
>
> forgive me if this question seems pretty basic but could 
> anyone tell explain this to me.
>
> i'm performing a practice assesment and i have located an IP 
> of a web based mail server (OWA).  this server is sitting 
> behind a hardware firewall (say PIX or Checkpoint)that is 
> NATing the IP Address to an internal non-routable address.  
> Now, if i use a tool such as Nmap to scan that external IP 
> are my scan results influenced by the Firewall.  Do firewalls 
> when NATing take all traffic from the external IP and pass it 
> to the internal nertwork and expect the server to have the 
> remaing services closed down or do they only take traffic 
> destined for a port and drop everything else.  if it's the 
> later, when i scan am i only scaning the 1 port that is 
> allowing traffic to be forward to it?
>
> Is there a way of determining if the firewall is blocking the 
> traffic to the other ports or if the Server has been locked 
> down and is blocking them?
>
> Any help would be appreciated.
>
> Regards
>
> Thatch
>
>
> --
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>
>
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