Subject: [tsvwg] UDP/IP outer as an IP-shim-IP tunnel and AMT as an example

From: Bob Briscoe <[email-masked]>
Date: Thu, 20 Jul 2017 10:26:40 +0100

David (as doc shepherd),

In the tsvwg mtg onTue, it was suggested that AMT ought to be included 
in the list of RFCs that define a new IP-shim-IP tunnelling protocol.

I said that I had actually looked at this and decided not to include it. 
I now remember why. It was cos AMT is just using UDP-IP encapsulation, 
not really defining a new encapsulation.

Nonetheless thanks to the guy who came to the mic (sry I can't remember 
the name - I think from Akamai) for making me revisit this. It 
identifies a gap: rfc6040update-shim doesn't mention general use of 
UDP-IP encapsulation. It only mentions the specific case of GUE (generic 
UDP encapsulation).

The way I propose to handle this is to add a bullet in 5. IP-in-IP 
Tunnels with Tightly Coupled Shim Headers 
<https://tools.ietf.org/html/draft-ietf-tsvwg-rfc6040update-shim-04#section-5> 
for UDP tunnels. Then add the following covering general use of UDP-IP 
encapsulation, giving AMT as one example of it:

       5.1.x UDP Tunnels

       Section 3.1.11 of the UDP usage guidelines in RFC 8085 already
       explains that a tunnel that encapsulates an IP header within a
       UDP/IP datagram, e.g. Automatic Multicast Tunneling (AMT
       [RFC7450]), needs to follow RFC 6040 when propagating the ECN
       field between inner and outer IP headers.

       The requirements in Section 4 update RFC 6040, so they add
       the important, but previously unstated requirement that, if
       the UDP tunnel egress does not, or might not, support ECN
       propagation, a legacy UDP tunnel ingress has to zero the outer
       ECN field, e.g. by configuration.

Do any RFC's need to be updated? No.
Given the UDP tunnelling section of RFC 8085 (UDP usage guidelines) 
already refers to RFC 6040, I don't think we need to update every RFC 
that uses UDP Tunnelling to refer to RFC 6040.

It would be ideal, but perhaps impractical.

Bob

-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/