Companies using public IP space owned by others for internal routing

Mark Andrews marka at
Mon Dec 18 02:34:38 CST 2017

> On 18 Dec 2017, at 1:20 pm, Robert Webb <rwebb at> wrote:
> Apologies for not responding sooner.
> This came to light with me on a forum where someone posted that they thought it strange that their MTA received an IP that is assigned to the DoD DNIC. 
> Where I work I have the opposite issue. They have a lot of public IPv4 space and only use it internally never be advertised to the internet. Something I have never agreed 
> With doing.
> Robert

Why?  This is a perfectly legitimate use of the IP addresses.  The purpose of assigning addresses is so that they are unique WORLD WIDE in whatever context you wish to use them in.


> -----Original Message-----
> From: Richard Porter [mailto:richard at] 
> Sent: Sunday, December 17, 2017 8:25 PM
> To: Robert Webb <rwebb at>
> Cc: nanog at
> Subject: Re: Companies using public IP space owned by others for internal routing
> Robert,
> I’ve heard of two cases recently, large companies (non carrier/ISP). One company looking to solve challenge with IPv6 and 6to4 and DNS.
> Also curious how wide-spread this is? Maybe just the kick in the butt for catching the elusive IPv6 unicorn?
> ~Richard
>> On Dec 17, 2017, at 3:30 PM, Robert Webb <rwebb at> wrote:
>> Will anyone comment on the practice of large enterprises using non RFC1918 IP space that other entities are assigned by ARIN for internal routing?
>> Just curious as to how wide spread this might be. I just heard of this happening with a large ISP and never really thought about it until now.
>> Robert

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at

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