who is responsible for keeping private IP addresses private?

[Seth Gordon]

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?

-- 
"The big dig might come in handy ... for a few project managers
 whom I think would make great landfill."  --Elaine Ashton
== seth gordon == sgordon at kenan.com == standard disclaimer ==
== documentation group, kenan systems corp., cambridge, ma ==
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