North American Network Operators Group
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Re: private ip addresses from ISP

  • From: Joe Maimon
  • Date: Tue May 23 11:37:49 2006 

Robert Bonomi wrote:


Date: Tue, 23 May 2006 11:14:53 -0400



"Translating" those addresses is a *BAD*IDEA*(TM).  That obscures who
the reporting machine was _if_ you have to actually communicate with that
network operator.





These are the options:



Construct the network so that icmp is never sourced from rfc1918



OR



Do either of below:



Filter icmp sourced from rfc1918 on egress



Dont filter icmp sourced from rfc1918 on egress



Translate icmp sourced from rfc1918 on egress



Use some feature that translates/replaces rfc1918 sourced icmp with
nonrfc1918 identifiable internally.




This is exactly why RFC1918 says that private-addrss source packets _should_
_not_ be passed across enterprise boundaries.  It does _not_ say 'must not',
because there *are* situations where it is necessary. This _is_ one of them. :)




You are in favor of:



Dont filter icmp sourced from rfc1918 on egress



However that leads to a significant hole in "anti spoofing defense
sheild" of the net.



So it becomes difficult to be in favor of this and also claim that
liberal application of anti-spoofing/urpf will solve most of the abuses
which depend on spoofing to be effective.






Understandably, translation on providers networks is not always feasible.



A feature on routers that sourced icmp packets to be told specificaly
which address of the router to source it from would also help.


When the router has only RFC1918 addresses (totally internal to the network),
it doesn't matter/help.




In this instance they would assign a single or more address nonrfc1918
to leverage this feature.




Also, the address to use as the source _is_ well-defined.  it is the interface
the packet came in on that triggered the ICMP message.




The proposed feature would make it configurable, perhaps on a per
interface basis.



The provider would keep an internal database. It need not even be routed.



It would be nice if this was completely an icmp packet field value and
not dependant on the ip header to identify the icmp generator.