Last Call Review of draft-ietf-lisp-rfc6833bis-13
review-ietf-lisp-rfc6833bis-13-tsvart-lc-perkins-2018-09-03-00

Request Review of draft-ietf-lisp-rfc6833bis
Requested rev. no specific revision (document currently at 25)
Type Last Call Review
Team Transport Area Review Team (tsvart)
Deadline 2018-08-31
Requested 2018-08-17
Draft last updated 2018-09-03
Completed reviews Rtgdir Last Call review of -13 by Jonathan Hardwick (diff)
Secdir Last Call review of -12 by Takeshi Takahashi (diff)
Tsvart Last Call review of -13 by Colin Perkins (diff)
Genart Last Call review of -13 by Pete Resnick (diff)
Genart Telechat review of -15 by Pete Resnick (diff)
Genart Telechat review of -24 by Pete Resnick (diff)
Assignment Reviewer Colin Perkins
State Completed
Review review-ietf-lisp-rfc6833bis-13-tsvart-lc-perkins-2018-09-03
Reviewed rev. 13 (document currently at 25)
Review result On the Right Track
Review completed: 2018-09-03

Review
review-ietf-lisp-rfc6833bis-13-tsvart-lc-perkins-2018-09-03

I've reviewed this document as part of the transport area review team's ongoing effort to review key IETF documents. These comments were written primarily for the transport area directors, but are copied to the document's authors for their information and to allow them to address any issues raised. When done at the time of IETF Last Call, the authors should consider this review together with any other last-call comments they receive. Please always CC tsv-art@ietf.org if you reply to or forward this review.

I have several concerns with the transport aspects of this draft. Many of these appear to be present in RFC 6833 also, but I note that while RFC 6833 is an Experimental, this draft is targeted at the Standards Track. Some of these issues may not be of practical concern, depending on the way LISP is used, and might just need clarifications in the draft to make it clear they do not occur in practice.

The draft defines the LISP control plane. It updates and greatly extends RFC 6833. The control plane runs over UDP, and this draft defines the format of LISP control plane messages and rules for processing such messages. The packet formats generally contain lists of records, the length of which is indicated by an 8-bit Record Count field located in a common sub-header. The format allows packets that are larger than the typical path MTUs seen in the Internet, but the draft doesn’t mention Path MTU discovery to determine the largest packet that can be sent, or how large packets are fragmented. Perhaps the messages are small enough that this is not a practical issue? In which case the draft should explain and justify this for each message type (and perhaps put limits on the Record Count to ensure it). Alternatively, then the draft should specify how path MTU discovery is to be performed, and how protocol messages should be fragmented (or subdivided) to fit the path MTU. Section 3.2 of RFC 8085 has some further discussion and suggestions for how to address this issue.

The draft does not mention congestion control, but many of the messages are rate limited. If the intent of the rate limits is that no further congestion control is needed, then it needs to be made explicit that this is the case, and some justification needs to be added to explain why it is safe. This could, perhaps, take the form of an appendix that analyses the expected control plane traffic that will flow over a particular path when the protocol is in use, and demonstrates that this will be low enough rate not to be problematic. In any case, the draft needs some discussion of how congestion control is addressed.

It’s unclear what messages need to be retransmitted if they’re lost, and how to determine if a message is lost (e.g., what is the timeout) and what is the retransmission schedule. This may be clear to a reader with an in-depth understanding of LISP, but it would be helpful to provide more explicit statements about loss detection and retransmission.

Many of these issues could perhaps be addressed by running the control plane over TCP rather than UDP, as is beginning to happen with the DNS. I understand that this would be a significant late change to the protocol.

The control plane messages contain embedded IP addresses. Does this cause any issues in the presence of NAT boxes, either by leaking information about private addressing or by distributing addresses that are unreachable outside their realm? I noticed there is a mention of an individual draft on LISP NAT Traversal in Section 5.6, but the embedded addresses are included in more places. 

Regards,
Colin