This is an HTML version of an attachment to the Freedom of Information request 'Internet Protocol (IPv4) address allocation'.

Corporate IT - Parliamentary Business 
Mr James Marten 
The Adelphi, 1-11 John Adam Street, 
e-mail: request-93643-
London WC2N 6HT  
[email address] 
CIT Freedom of Information Mailbox 
02 December 2011 
Sent by e-mail 
Ref No: 
Dear Mr Marten, 
Thank you for your Freedom of Information requests made on 18 November 
2011 in which you said: 
“You have assigned to you a Class A block of Internet protocol 
version 4 (IPv4) addresses, the range from to containing approximately 16 million addresses. This 
is listed at: 
and can be confirmed by a WHOIS query. 
     The information that I would like to request is: 
     1. Please confirm that this IPv4 address block is assigned to and 
     owned by the DWP or a subsidiary department. 
     If the answer to that is "yes", 
     2. Are any addresses or address ranges within this block in use on 
     the public Internet for departmental IT, communications or other 
     functions? If so, please indicate approximately how much of the 
     address space is in use. 
     3. Are any addresses or address ranges within this block in use 
     within any internal infrastructure (i.e. not accessible from the 
     public Internet) for departmental IT, communications or other 
     functions? If so, please indicate approximately how much of the 
     address space is in use. 
     4. Please indicate whether any consideration has been given, if 
     practical (depending on the answers to the two previous questions) 
     as to whether this address block, or part of it, could be released 
     for reassignment.” 
Our Reply 

1.  We can confirm that the address block is assigned to the DWP. 
2.  In principle, none of the address space is exposed to the public Internet. 
There may be a very small number of addresses that have been exposed for 
specific purposes, but certainly no significant block of addresses is visible 
from the public Internet. 

3.  The address space is already shared across government. We have used or 
allocated approximately 80% of the address space, and have earmarked the 
remaining space for use within the proposed Public Services Network (PSN). 
The PSN is building an Internet for government, and the DWP address space 
is a key building block for delivery of this. 
4.  DWP have no plans to release any of the address space for use on the public 
Internet. The cost and complexity of re-addressing the existing government 
estate is too high to make this a viable proposition. DWP are aware that the 
worldwide IPv4 address space is almost exhausted, but knows that in the 
short to medium term there are mechanisms available to ISPs that will allow 
continued expansion of the Internet, and believes that in the long term a 
transition to IPv6 will resolve address exhaustion. Note that even if DWP were 
able to release their address space, this would only delay IPv4 address 
exhaustion by a number of months. 
If you have any queries about this letter please contact us on CIT Freedom of 
Information Mailbox
, quoting the above reference number.   
Yours sincerely, 
Phil Tomlinson 
Corporate IT 
Department for Work and Pensions 
Your right to complain under the Freedom of Information Act 
If you are not happy with this response you may request an internal review by e-mailing freedom-of-information-
[email address] or b
y writing to DWP, Central FoI Team, 5th Floor, The Adelphi, 1-11, John Adam Street, 
London WC2N 6HT. Any review request should be submitted within two months of the date of this letter.  
If you are not content with the outcome of the internal review you may apply directly to the Information 
Commissioner’s Office for a decision. Generally the Commissioner cannot make a decision unless you have 
exhausted our own complaints procedure. The Information Commissioner can be contacted at: The Information 
Commissioner’s Office, Wycliffe House, Water Lane, Wilmslow, Cheshire SK9 5AF