Subject: [tsvwg] RFC5405bis draft WGLC: Encapsulation considerations

From: "Black, David" <[email-masked]>
Date: Mon, 21 Sep 2015 23:01:48 +0000

<WG chair hat OFF>

These comments are made as an individual from my recent experiences (scars
included) in working on two UDP encapsulations of relatively general purpose
protocols, MPLS (see RFC 7510) and GRE (draft-ietf-tsvwg-gre-in-udp-encap,
Work in Progress).

The 5405bis draft currently contains a relatively general cross-reference
to draft-ietf-rtgwg-dt-encap in section 3.1.  I would like to see this made
more specific with individual areas of the 5405bis draft cross-referenced
to the corresponding material in the rtgwg-dt-encap draft.  A normative
reference to the rtgwg-dt-encap draft may be appropriate as part of this.

The references to RFC6935 and RFC6936 in Section 3.4 do not (IMHO) adequately
convey the difficulty (pain and suffering - no, I'm not kidding) that awaits
those who undertake design to comply with those RFCs without using a header
checksum.  I would like to see a strong recommendation (lower case "should" in
the form of "really ought to" may suffice) that in full generality, the quality
of the networking equipment over which IPv6 is and will be run in the Internet
in general is highly variable, and therefore:

	- New encapsulation designs really ought to include a header checksum
		that covers at least the IPv6 header, the UDP header and the shim
		header for the encapsulation, if any.  This is a misdelivery
		countermeasure, as misdelivery concerns have been the primary
		source of the "pain and suffering" ;-).

	- RFC 7510 (MPLS/UDP) is the proverbial "exception that proves the rule"
		due to the relatively strong assertions that can reasonably be
		made about the quality of networking equipment over which MPLS
		is and will be run, and some of the restrictions that are within
		reason for MPLS/UDP equipment, but unreasonable in general.
		Attempting to apply the MPLS/UDP approach to omitting UDP checksums
		[for IPv6] to GRE/UDP in full generality has not worked.

The congestion control discussion for UDP tunnels (3.1.9) and possibly UDP
in general (3.1) should call out the "two scopes of applicability with
different requirements" approach that this WG has adopted for GRE/UDP as
useful.
See: https://mailarchive.ietf.org/arch/msg/tsvwg/1_h9_RJAEyXhW9q3utUXUnwWvbU

This sort of approach can avoid stretching a single protocol design and/or
set of requirements to try to cover well-managed/operated networks and the
"wild west" infrastructure/equipment that is included in the Internet in
general.

</WG chair hat OFF>

Thanks,
--David
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David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
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