I have reviewed this document as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review.  Document editors and WG chairs should treat these comments just like any other last call comments.   By extending basic CoAP with two block options and two block sized, this document provides a mechanism to transfer larger representations in a block-wise fashion. It is well written, especially security section. In addition, Several examples are provided to show how to use block options. Interaction between CoAP and HTTP and interaction between Block option and other options and aspects are also discussed. I think this document is ready for publication. Here are a few editorial comments: 1.        Section 2, 2nd paragraph Section 2 said “ In identifying these options, we use the number 1 to refer to the    transfer of the resource representation that pertains to the request,    and the number 2 to refer to the transfer of the resource   representation for the response ” Where to encode number 1 and number 2 for two separate options? 2.        Section 3.1, 1st paragraph “ The first example (Figure 2) shows a GET request that is split into three blocks.  The server proposes a block size of 128, and the client agrees.  The first two ACKs contain 128 bytes of payload each, and third ACK contains between 1 and 128 bytes. “ s/”128 bytes of payload”/” payload of 128 bytes” s/”between 1 and 128 bytes”/”payload between 1 and 128 bytes” 3.        Section 3.1, figure 2 Is MID abbreviation of “Message ID”, would you like to expand it? 4.        Section 4, 2 nd paragraph s/is already/has already 5.        Section 4, 2 nd paragraph Since Size1 has already defined in [RFC7252], I am wondering whether this draft need to update RFC7252 since it looks Size1 is redefined in this draft. Is there any update to IANA section for Size1 registry? 6.        General comment: Is there possible to provide an example to show how to use block size together with block option?   Cheers! -Qin Wu