Are you sure it can't find, deny, and log spoofed
connections?

http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_v53/syslog/pixemapa.htm

search for spoof...

> The only way I know of for a Pix, or any type of
> box, to identify spoofing 
> is by filters that know which source addresses are
> permissible for 
> incoming traffic on an interface.  With some Cisco
> IOS versions (not 
> available on Pix) you can use "ip verify unicast
> reverse-path" - a very 
> nice trick that uses the box's routing table to
> determine whether to allow 
> a source address.  The address, when used as a
> destination, must be routed 
> out the same interface it arrived on; else it gets
> discarded.  Boxes 
> without such a nice control have to have hardcoded
> access lists which 
> statically permit only the source addresses that the
> admin thinks should 
> be arriving on an interface.
> 
> But that only works for interfaces which don't have
> a default route and 
> that don't use dynamic routing (which is not,
> unfortunately, an issue on 
> the Pix).  If the Pix is connected to the Internet
> typically its outside 
> interface will be configured with a default route. 
> There is no way it can 
> identify or block spoofed traffic arriving at such
> an interface (but it 
> can, if so configured with access lists, block
> address ranges that it 
> knows should never arrive on that interface, such as
> rfc1918 addresses and 
> its own inside address ranges).
> 
> My answer to the original question is that Pix
> cannot identify spoofing 
> (but it can statically filter by address, which may
> be used to block 
> spoofing in some cases).


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