ISP verification of a reserved private ip, can someone explain this to me?

I placed an order for a customer today for a trial certificate for a private ip address ( I received the following response from Comodo support.

In order to validate your IP(, kindly provide us the domain ownership document which is sufficient to validate your IP. This can be any letter/document from your ISP/Registrar which states your domain name and your company name.

I am totally baffled. How am I supposed to get this information from an ISP for a ip address which is in the class B range for Private Internets?

RFC1918 could not be more clear on this (RFC 1918 - Address Allocation for Private Internets (RFC1918)).

3. Private Address Space

The Internet Assigned Numbers Authority (IANA) has reserved the
following three blocks of the IP address space for private internets:        -  (10/8 prefix)
 [b]      -[/b]  (172.16/12 prefix)     - (192.168/16 prefix)

We will refer to the first block as “24-bit block”, the second as
“20-bit block”, and to the third as “16-bit” block. Note that (in
pre-CIDR notation) the first block is nothing but a single class A
network number, while the second block is a set of 16 contiguous
class B network numbers, and third block is a set of 256 contiguous
class C network numbers.

An enterprise that decides to use IP addresses out of the address
space defined in this document can do so without any coordination
with IANA or an Internet registry. The address space can thus be used
by many enterprises.

I would love it if someone could explain this to me.

thanks much

  • Doug

Welcome at the forums (:WAV)

These IP ranges: - - - -

are valid for private networks only.

In Internet terminology, a private network is a network that uses RFC 1918 IP address space. Computers may be allocated addresses from this address space when it is necessary for them to communicate with other computing devices on an internal (non-Internet) network but not directly with the Internet.

The IP you provided is valid only for lans. It is not a valid internet adress :wink:

For finding your real IP go at this site

hope it helps,

Right exactly.

So the question is why am I being told that I need to have my ISP verify that this ip address belongs to me in order to have this certificate issued?

BTW: I wasn’t asking for explanation of private addressing, I am quite familiar with it. I was trying to ask in a nice way why am I am being asked for this ridiculous verification.

This is to funny. I just noticed the link you provided to the wikipedia article. that was the exact same link I provided in my response to the verification request from Comodo support.

Below is the exact response I sent them, to which they simply asked me for the ISP verification of this ip address again.

172.21.x.x is in the Class B reserved private ip address range and cannot be used on the internet. Internet routers don't route ip numbers in that range.

You can also see the whois record shows the ip is reserved by iana.

Private network - Wikipedia

for some reason our system is not picking that IP as internal.
I asked them to take a look at it…
i am sure they will resolve it…

thanks for the heads up.


Sure no problem. Is this something you can help me with? If so I’ll glady provide the order number.

thank you


I checked today with the validation team and the order was issued today 13/12/2006.


Yes I know, thank you.