Private use of non-RFC1918 IP space

Stephen Sprunk stephen at
Mon Feb 2 20:52:43 UTC 2009

TSG wrote:
> I find it really troublesome to believe that the subnetting on a site 
> was so complex that it ate an entire /8. What I am betting is that for 
> some reason that ISP wants its addressing to be totally flat and not 
> replicated.

The subnetting doesn't need to be "complex"; they may simply have a 
large number of small sites, or a moderate number of relatively large 
sites, that will eat up more than a /8's worth of addresses.  There _do_ 
exist companies with 100,000+ locations and a few dozen devices per 
location; throw in the necessary aggregation so the routers don't fall 
over and you're looking at NATing multiple instances of 10/8 -- and I 
know from experience that's not fun.

However, the OP implies that his problem is caused by a poor subnetting 
scheme in 10/8; the correct solution in that case is to fix the 
subnetting -- but mgmt may not be willing to pay the labor (or other) 
costs of that.


Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking

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