Subject: Re: [bess] [Idr] I-D Action: draft-rosen-idr-tunnel-encaps-03.txt

From: Eric C Rosen <[email-masked]>
Date: Mon, 17 Aug 2015 14:12:48 -0400

On 8/6/2015 9:50 PM, Xuxiaohu wrote:
> Hi co-authors,
>
> Thanks for this update which looks much better.
>
> I still have three questions as follows:
>
> 1. This draft assumes that NVGRE adopts the same approach to carrying
> IP traffic as VXLAN. However, NVGRE has a protocol field and
> therefore it could directly carry IP traffic w/o adding the fake
> Ethernet header between the IP payload and the GRE header (see
> https://www.ietf.org/mail-archive/web/nvo3/current/msg01520.html and
> http://tools.ietf.org/html/draft-yong-l3vpn-nvgre-vxlan-encap-03#page-3.)
> Hence, how about considering the simpler layer3 overlay for NVGRE?

Our reference for the NVGRE encapsulation was 
draft-sridharan-virtualization-nvgre-08.txt, which is now on the RFC 
Editor's queue for publication as an Informational draft in the 
"Independent Submissions" stream.  That RFC-to-be only discusses the use 
of NVGRE to carry ethernet frames.  Draft-yong-l3vpn-nvgre-vxlan-encap 
discusses the use of NVGRE to carry IP packets (analogous to VXLAN-GPE), 
but that draft is expired.

I have no objection to incorporating the idea of draft-yong into the 
tunnel-encaps draft, if that's what the relevant WGs support, but it 
would be nice to see some further discussion first.

>
> 2. It said "...Note that if none of the TLVs specifies the MPLS
> tunnel type, a Label Switched Path SHOULD NOT be used." IMO, since
> the LSP is signaled by label distribution protocols such as LDP,
> RSVP-TE or L-BGP, why is it still necessary to specify the tunnel
> encapsulation attribute to indicate whether or not an LSP should be
> used.

If the tunnel encapsulation attribute is present, identifying one or 
more tunnel types, the semantics are that one should try to send packets 
through one of the identified tunnel types (if possible).  So if MPLS is 
not specified as one of the tunnel types, the use of an MPLS LSP for 
transport would have to be avoided.  The presence of a TLV identifying 
an MPLS tunnel type would indicate that the use of an MPLS transport 
tunnel is one of the permissible options for transmitting the packets.

> 3. Since this draft has mentioned the encapsulation of MPLS over
> VXLAN/NVGRE, would you please give any clue to the scenario of this
> special encapsulation?

Any IP-based overlay should be able to pass an MPLS packet with an 
arbitrary label stack.