Last Call Review of draft-ietf-dime-nat-control-
review-ietf-dime-nat-control-secdir-lc-lepinski-2011-03-11-00

[I apologize if you received this message twice]



I have reviewed this document as part of the security directorate's 


ongoing effort to review all IETF documents being processed by the


IESG.  These comments were written primarily for the benefit of the 


security area directors. Document editors and WG chairs should treat 


these comments just like any other last call comments.






This document defines a Diameter application whereby a Diameter NAT 


Control Application (DNCA) server (either a AAA server or a Network 


Access Server) can control a DNCA client (either a NAT or NAPT device). 


For example, the DNCA server can determine the number of port bindings 


available to a given host, cause the allocation of particular NAT 


bindings, define the external address pool used for by the NAT device, 


or generate reports used for accounting purposes.






The principle security concern is that an unauthorized (or 


unauthenticated) DNCA server could effect a denial of service of attack 


on any or all hosts using a NAT/NAPT device in several ways. (E.g., an 


unauthorized server could exhaust resources in the NAPT device, set 


maximum bindings to zero for all hosts, provide a set of external 


addresses that are in use elsewhere in the network, etc.) An additional 


concern is that an unauthenticated DNCA client could provide incorrect 


reporting data to the DNCA server to prevent correct accounting within 


the system. Therefore, the NAT control application requires mutual 


authentication, authorization of the DNCA server, and integrity 


protection of the Diameter messages in the DNCA interaction. 


Additionally, the application may require confidentiality depending on 


the deployment scenario and, particularly, how authorization is 


accomplished.






The Security Considerations section of the document claims that security 


considerations are essentially the same as in the Diameter QoS (RFC 


5866). I agree with the authors that the security concerns for Diameter 


NAT Control are very similar to the security concerns for Diameter QoS, 


but I think the additional layer of indirection is not helpful to the 


reader. (In particular, the NAT Control Application has no dependencies 


on the Diameter QoS document. Therefore it is reasonable to believe that 


an implementer of Diameter NAT Control may not be familiar with the 


Diameter QoS document.) I would recommend that the authors add 


additional text explaining why mutual authentication, server 


authorization, and message integrity are required (copying a bit of text 


from RFC 5866 may be appropriate). Then I would recommend that the 


authors cite the Diameter specification (RFC 3588) for a discussion of 


how IPsec or TLS can be used to obtain these security properties. (To 


me, this seems preferable to sending a reader to RFC 5866 for discussion 


of required security properties, which in turn sends the reader to RFC 


3588 for an information on the use of IPsec or TLS to achieve these 


properties.)






Finally, the end of the security considerations section claims that 


"Authorization between DNCA Agent and


   DNCA Manager is beyond the scope of this document". I understand 


that the authors do not want to mandate a particular mechanism for 


making an authorization decision. That being said, providing some 


guidance as to how a DNCA client would determine if a DNCA server were 


authorized to issue NAT control commands. I imagine in practice that the 


way authorization is accomplished is that the NAT/NAPT device stores a 


local authorization policy. (E.g., the device stores a list of server 


identities that authorized, and then once the server has been 


authenticated its identity can be checked against the list). At the very 


least having text analogous to first paragraph of RFC 5866 Section 11 


would be helpful (RFC 5866 says the device making the authorization 


decision needs to have sufficient information to make this decision and 


then provides examples of where this information would come from.)




- Matt Lepinski