[BLU] who is responsible for keeping private IP addresses private?

[david at thekramers.net (David Kramer)]

On Tue, 30 Jan 2001, Seth Gordon wrote:

> Suppose I have two machines connected to the same DSL router: Public, with
> a generally-accessible IP address, and Private, with 192.168.1.1.  E.g.,
> Public could be a domain's mail server, and Private could be a workstation
> that downloads the mail.
>
> Is there any way for an attacker elsewhere on the Net to impersonate
> 192.168.1.1?  (In other words, if Public trusts everything it receives from
> 192.168.1.1, can an attacker exploit that trust relationship as a first
> step to cracking Public?)  If not, what part of the network infrastructure
> prevents this from happening?
>
>

Yes.  That is why most cablemodem users have a firewall with two network
cards- one going to the cablemodem and one going to the intranet.

There is something called source-routed packets that can accomplish what
you talk about.  also there may be an arp trick if they get the MAC number
of the private machine (that's just a theory of mine though).

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