Subject: [tsvwg] RFC 5405bis draft - non-congestion-controlled IP traffic

From: "Black, David" <[email-masked]>
Date: Wed, 29 Jun 2016 14:01:39 +0000

A while back, in response to Martin Stiemerling's comments on the GRE/UDP draft,
I wrote:

> [2] IP traffic congestion control assumptions.
> 
> > - I do disagree with "IP-traffic can be assumed to be
> > congestion-controlled.", even though it is stated in RFC 5405, as there
> > is a lot of IP traffic that is not congestion controlled, such as
> > multicast traffic...
> > Section 4, even states that multicast and broadcast traffic can be
> > carried over GRE-UDP! None of both is in general congestion controlled!
> 
> Well, this is actually an issue with the rfc5405bis draft, and this issue needs
> to be fixed there, as RFC 5405 is (and the rfc5405bis draft will be) the
> Transport Area's statement to the rest of the IETF on congestion control
> guidelines and requirements for UDP usage.

This is indeed an issue with the 5405bis draft.  In particular, Martin has
effectively pointed out that this text in Section 3.1.11 is wrong because
it encompasses multicast and broadcast traffic:

   IP-based traffic is generally assumed to be congestion-controlled,
   i.e., it is assumed that the transport protocols generating IP-based
   traffic at the sender already employ mechanisms that are sufficient
   to address congestion on the path.  Consequently, a tunnel carrying
   IP-based traffic should already interact appropriately with other
   traffic sharing the path, and specific congestion control mechanisms
   for the tunnel are not necessary.

Changing "IP-based traffic" to "IP-based unicast traffic" in three places
in the above paragraph should correct this problem.

In addition, multicast needs to be called out as an exception in the next
paragraph:

OLD
   However, if the IP traffic in the tunnel is known to not be
   congestion-controlled, additional measures are RECOMMENDED to limit
   the impact of the tunneled traffic on other traffic sharing the path.

   The following guidelines define these possible cases in more detail:
NEW
   However, if the IP traffic in the tunnel is known to not be
   congestion-controlled, additional measures are RECOMMENDED to limit
   the impact of the tunneled traffic on other traffic sharing the path.   For
   the specific case of a tunnel that carries IP multicast traffic, see section 4.1.

   The following guidelines define these possible cases in more detail:

As a WG chair and draft shepherd, I think these changes are important,
as the original text has already been misread/misinterpreted by more
than one UDP tunnel designer.

Thanks, --David

---

From: "Eggert, Lars" <[email-masked]>
Date: Thu, 30 Jun 2016 07:45:27 +0000

I made both of these changes in our working copy of -16. Will wait a little while before submitting in case there are more change requests.

Thanks,
Lars