Subject: Re: WG last call review of draft-ietf-6man-segment-routing-header

From: "C. M. Heard" <[email-masked]>
Date: Mon, 30 Apr 2018 09:29:25 -0700

I noticed some nits in the -12 version:

- The acronym OIF is not expanded on first (and only) use. This may already
be in the list of nits from Adrian Farrel's review.

- In section 3 (page 7) the HMAC data is said to be found in the last 36
octets of the header. This excludes the RESERVED field. In section 3.1.2 it
is said to be found in the last 38 octets of the header. This includes the
RESERVED field. It would be best to pick one consistent convention.

- Why do the suggested codepoints for the PAD0 and PADN TLVs (128 and 129,
respectively) have the MSB set to indicate that they can change in transit?
Given that the length of the SRH cannot change in transit, it would seem
that these options should not be mutable. If AH is actually used, making
them immutable would prevent injection of covert data by an intermediate
node.

- It seems to me that the following text in Section 5.2

   As a generic security measure, any service provider will block any
   packet destined to one of its internal routers, especially if these
   packets have an extension header in it.

would be clearer (and more accurate) if changed to something on the lines of

   As a generic security measure, a service provider may block all
   packets from external sources destined to one of its internal
   routers, especially if these packets contain extension headers.

- Section 7.2: for clarity, the TLV registry should probably be split into
mutable and immutable TLVs.

Mike Heard