Subject: [tsvwg] partial review of draft-ietf-tsvwg-gre-in-udp-encap-03

From: Bob Briscoe <[email-masked]>
Date: Fri, 21 Nov 2014 17:30:18 +0000

Lucy,

I'll wait for David's promised proposal to the list before commenting 
on the checksum issue.

1) Regarding congestion control, I do not share the position of some 
others in tsvwg. Congestion responsiveness is determined by how the 
source spaces out the packets (i.e. their instantaneous rate). Just 
because a tunnel ingress encapsulates a packet with a UDP header does 
not suddenly make it unresponsive to congestion. The spacing between 
packets is still determined by the source. So there is no need to 
even mention congestion control considerations in a tunnelling 
document, except to say in the scoping at the start that the addition 
of tunnel headers is completely orthogonal to congestion avoidance and control.

2)
Please replace:
    Tunnel end points that support
    ECN MUST use the method described in [RFC6040] for ECN marking
    propagation.
With:
    Tunnel end points need to use the method described in [RFC6040] 
for ECN marking
    propagation.
Rationale:
    i) There is no such thing as a tunnel end point that does not 
support ECN - it has to put something in the ECN field, and it would 
not be appropriate to put anything in there other than what RFC6040 says.
   ii) Generally it is not a good idea to fill one draft with 
normative statements that repeat normative statements made in other 
drafts. Otherwise updating an RFC gets very difficult - we have to 
update all the other RFCs that gratuitously repeat what it says.

3) Nit in section 3.1.
    Section 5 of RFC6936 [RFC6936] specifies the additional requirements
    that implementation of UDP zero-checksum over IPv6 MUST compliant
    with. To compliant with it, the following additional requirements
    apply
s/compliant/comply/ (twice)

There are other nits, but they can be dealt with later.

Cheers

Bob

________________________________________________________________
Bob Briscoe,                                                  BT

---

From: "Black, David" <[email-masked]>
Date: Fri, 21 Nov 2014 19:03:49 +0000

Bob,

> I'll wait for David's promised proposal to the list before commenting

Don't hold your breath waiting for this one, but you might take a look
at the text on UDP zero checksums for IPv6 in draft-ietf-mpls-in-udp for
a more contained worked example.  The overall approach is applicability
restrictions (networks on which it is ok vs. not ok to use UDP zero
checksums for IPv6) plus additional header checks at tunnel egress -
if/when those are objectionable, turn on full UDP checksums.

> even mention congestion control considerations in a tunneling

Unfortunately, it's not "completely orthogonal" because UDP goes many
places that the encapsulated protocols can't.  Hence "can't get there
from here" protection in NATs and other middleboxes that drop the
unencapsulated protocol won't stop non-congestion controlled UDP-
encapsulated traffic from getting into places that it shouldn't and
causing damage.  Also, please take note of the text in the mpls-in-udp
draft that recommends filters to block such traffic from going where
it shouldn't, which restores some of these protections.

Thanks,
--David

> -----Original Message-----
> From: Bob Briscoe [mailto:[email-masked]]
> Sent: Friday, November 21, 2014 12:30 PM
> To: Lucy yong
> Cc: Black, David; [email-masked]
> Subject: partial review of draft-ietf-tsvwg-gre-in-udp-encap-03
> 
> Lucy,
>