Telechat Review of draft-ietf-intarea-ipv4-id-update-
review-ietf-intarea-ipv4-id-update-secdir-telechat-kent-2012-07-05-00

I 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, "Updated Specification of the IPv4 ID Field" is a 


update of RFCs 791, 1122 and 2003. The primary motivation for the 


update is a recognition that the uniqueness requirement imposed on 


the field values (on a per host pair and protocol basis) would limit 


"connections" to about 6.4 Mb/s (for typical 1500 byte packets), an 


unrealistically low data rate today. This document updates the cited 


RFCs to reflect current practice and to more closely match IPv6. 


Specifically, the field value is defined only when a datagram is 


fragmented.






The Security Considerations section is very brief, only three 


paragraphs.  It notes that removing the prior constraints on ID field 


generation (MSL uniqueness) make it easier to use this field as a 


covert channel. It suggests that rewriting the field is a possible 


countermeasure. This advice is presented with the context of 


datagrams not protected using AH. Because AH is no longer a mandatory 


to implement element of the IPsec suite, I suggested an edit to avoid 


suggesting that AH use if common.






The text goes on to discuss how removing the MSL uniqueness 


requirement reduces the entropy associated with the IPv4 header. It 


fails to explain why this might be significant. There is no 


indication that modern encryption algorithms used IETF security 


protocols are harmed by this reduction in entropy. Thus the paragraph 


devoted to this issue seems extraneous, possibly confusing to 


implementers.






The final paragraph in this section notes that the proposed ID field 


conventions may make it more difficult to count the number of 


distinct devices behind a NAT or similar device. I agree with the 


author's observation that this side effect of the current ID field 


requirements is not a security feature per se and thus not a concern.






Earlier sections of this document do a good job explaining how this 


change may impact various forms of middleboxes. The author should 


note in the SCC whether the change proposed in this document may 


adversely affect availability, if these devices are not updated to 


account for this change.

Attachment:


draft-ietf-intarea-ipv4-id-update-05.pdf




Description:

 Adobe PDF document