[CentOS] Addressing outgoing connections to a specific interface

Lamar Owen lowen at pari.edu
Sat Nov 6 17:42:01 EDT 2010


On Nov 6, 2010, at 5:19 PM, Bob McConnell wrote:

> But I still wonder if you are unique in finding this address  
> collision,
> or do others also have the same problem? If it is widespread, then it
> should be solved by the people managing those devices.


Nah; one of the prominent use cases for NAT on Cisco routers is  
linking between two overlapping networks. (see http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_example09186a0080093f30.shtml 
  )

This happens when companies merge, for instance, and both of them used  
the same or overlapping RFC1918 networks; happens a lot with  
10.0.0.0/8 and 192.168.0.0/16 (mostly in the 192.168.0.0/24 and  
192.168.1.0/24), not so much in 172.16.0.0/12 (which then becomes a  
popular pool to NAT the overlappers to).  Judicious NAT and split DNS  
help solve the problem until things can get renumbered.  Large  
networks never do get renumbered, and NAT between enterprise networks  
lives on.

IPv6 includes a large block of ULA addresses to hopefully reduce  
collisions of this sort for non-globally-routed addresses.
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