RE: Possibility of routing through internet with private IP address

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

  I've had no trouble mixing bogon filters (i.e., block invalid
or spoofed source addresses such as private ranges) with VPN
tunnels, even when both were on the same NetScreen box.  At the
point that the tunnelled traffic hits the filters, it's encapsulated
within packets bearing public IP addresses.

David Gillett

> -----Original Message-----
> From: e-bone [mailto:ebone () DotsAndLoops net]
> Sent: October 16, 2003 09:01
> To: security-basics () securityfocus com
> Subject: Possibility of routing through internet with private 
> IP address
>
>
> Hi,
> We have the following VPN/Firewall setup:
>
> WAN -- T1 router -- netscreen(VPN) -- SonicWall(Firewall) -- LAN
>
> NAT takes place at the SonicWall.
>
> VPN tunnels from the WAN side end at the netscreen.
> VPN users receive a "virtual" IP address of 172.31.1.*,
> 172.31.2.* , etc ... 
>
> The SonicWall has rules allowing in these private address ranges.
>
> Now, the question ....
> My (doofus) boss seems to think that it is possible that somebody
> could come into our LAN from the WAN side with one of these private IP
> addresses ?
> I tend to think this is complete hogwash (or bollocks if you prefer).
>
> Is there anyway someone can route through the internet (WAN) with a
> private IP address, and have the packets routed back to them 
> properly ?
>
> For the purposes of answering the question, disregard for the moment
> that we could set up the netscreen with policies requiring 
> these private
> IP ranges to be tunneled .... my boss for some inexplicable reason
> has no faith in this device ... that is the whole reason we still
> have the SonicWall around too.
>
> Any tips, hints, or gibberish of any kind welcome.
>
> cheers,
> e
>
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- Make firewall, VPN, and NAT rules interoperable across heterogeneous
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