North American Network Operators Group
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Re: RFC 1918

  • From: Danny McPherson
  • Date: Fri Jul 14 15:15:01 2000 
> We had a similar discussion a long while ago (2 years?) on whether having 
> RFC1918 addressed router interface could break Path MTU discovery.
> 
> The general upshot is that the RFC specifically says that no packets with a 
> reserved address in the header (source or destination) should leave the 
> network in question.  Also, the RFC says it is not at all unreasonable (but 
> not required) for a network to filter packets with RFC1918 addresses in the 
> source.  (To prevent attacks and things like that.)
> 
> So it is nearly impossible to stay 100% compliant and address router 
> interfaces with RFC1918 addresses.  (Unless you NAT or something.)

Of course, if you use RFC1918 space for internal addressing, 
then filter all RFC1918 SA both ingress _and egress to your 
network, you'd in theory be 100% compliant (whatever that
means).   You'd just be handicapping traceroute, PMTU and 
the like .. but of course, if folks have a problem with it :-) 

-danny