The Department of Work and Pensions, UK has an entire /8

Cutler James R james.cutler at
Wed Sep 19 14:07:52 UTC 2012

On Sep 19, 2012, at 9:24 AM, John Osmon <josmon at> wrote:
> On Wed, Sep 19, 2012 at 12:07:33AM -0500, Jimmy Hess wrote:
>> Assume you have a public IPv4 assignment,   and someone else
>> starts routing your assignment...  "legitimately" or not, RIR allocation
>> transferred to them, or not.
>> There might be a record created in a database, and/or internet routing
>> tables regarding someone else using the same range for a connected network.
>> But your unconnected network, is unaffected.
> Ahh...  But the network may not be unconnected.  Just because *you*
> don't have a path to it doesn't mean others are similarly disconnected.
> All of those "others" would be affected.
>> You are going to have a hard time getting a court to take your case,
>> if the loss/damages to your operation are $0,  because your network is
>> unconnected, and its operation is not impaired by someone else's use,
>> and the address ranges' appearance in the global tables.
> Think about a company that has thousands of private interconnects with
> other companies.  Unique address space would remove the chance of
> RFC1918 space clash, and any of the bad effects of NAT. (e.g The network
> *works* as it was originally designed.)
> Such a network would not have $0 in loss/damage when the partners can't
> reach it due to a rogue announcement.
> The Internet is not the same from all viewpoints.

This discussion is repeating ones heard hear in the mid 1990s.  

Having a block of IP addresses not seen in YOUR IP routing tables is NOT evidence of unused addresses. For example, an inter-network SMTP relay correctly forwards messages via MX DNS entries only if unique IP address exist on both sides of the relay. This is just one example of application level gateways used to isolate networks at Layer 3 that has been in use for decades.  

As noted above, there are many instances of private interconnects which rely on assigned integers to tag destinations in a globally unique fashion.  In the case of IP addressing, IANA and the various registries provide this globally unique assignment service.  Use of these unique integers for packet routing is left as an exercise for the Network Engineer.  IANA and the registries are not in the business of directly policing the use of any assigned integers.

Those of us who have been involved in interconnecting private networks with overlapping IP address assignments are well aware of the pitfalls, hazards, and costs of using non-unique addressing. 

An entity which uses its ignorance of how addresses are used internally by another entity as an excuse to ignore proper IP address assignment is deliberately contributing to network chaos and to the culture of ignoring rules "because we can".

The bottom line is that "Connected" does not mean "Routable via IPv4/IPv6". This is in addition to "Hidden" does not mean "Unused" as pointed out by others.

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