please see inline (“...FB“)
From: nvo3 <nvo3-boun...@ietf.org> On Behalf Of ???(??)
Sent: Freitag, 13. April 2018 09:42
To: Int-area <int-area-boun...@ietf.org>; Frank Brockners (fbrockne)
Cc: NVO3 <firstname.lastname@example.org>; int-area <int-a...@ietf.org>; Service Function
Chaining IETF list <s...@ietf.org>; IETF IPPM WG <i...@ietf.org>
Subject: Re: [nvo3] [Int-area] [ippm] encapsulation of IOAM data in various
protocols - follow up from WG discussion in London
It said in draft-brockners-ippm-ioam-vxlan-gpe-00:
[I-D.ietf-nvo3-vxlan-gpe] defines an "O bit" for OAM packets. Per
the O bit indicates that the packet
contains an OAM message instead of data payload. Packets that carry
IOAM data fields in addition to regular data payload / customer
traffic must not set the O bit. Packets that carry only IOAM data
fields without any payload must set the O bit."
My first question is: if the Next Protocol field within the VXLAN-GPE header
should be resorted to indicate the IOAM, why do we still need the "O" bit?
...FB: What this paragraph states is that IOAM is orthogonal to the O-bit in
traffic and will not impact the use of the O-bit. I.e. if the O-bit is set on
traffic (because it is OAM traffic), then you’ll continue to have it set with
IOAM data added to the packet. If the O-bit isn’t set on the original packet,
then it also won’t be set with IOAM data added to the packet.
It said in draft-brockners-ippm-ioam-vxlan-gpe-00:
"Next Protocol: 8-bit unsigned integer that determines the type of
header following IOAM protocol. The value is from the IANA
registry setup for VXLAN GPE Next Protocol defined in
My second question is: why the "Next Protocol" is designed to be
context-specific (i.e., specific to the tunnel over which the IOAM data fields
are contained). In other words, wouldn't it be better to make the Next Protocol
tunnel-independant since the IOAM is intended to be added into various tunnel
...FB: In those cases where IOAM data encapsulation uses the “next protocol”
approach, the encapsulation will borrow next-protocol code points from the
“parent” protocol. It is the parent protocol that determines how these code
points are structured and defined – and in some cases they are 16-bit (like
with GRE, where “next protocol” is an Ethertype value) or 8-bit, like for
example for “NSH next protocol”
My third question is: does it means intermediate nodes must be aware of various
tunnel encapsulations since the IOAM data field is behind the tunnel header?
wouldn't it be better to carry the IOAM data just behind the outer IP header?
...FB: This is really a deployment question. E.g. if you run VXLAN-GPE over
IPv6, you could choose to encapsulate IOAM data natively into IPv6, or you
could choose to encapsulate IOAM data into VXLAN-GPE, or even both.
On Wed, Apr 11, 2018 at 12:02 PM, Frank Brockners (fbrockne)
Back at the IPPM meeting in London, we discussed several drafts dealing with
the encapsulation of IOAM data in various protocols
draft-weis-ippm-ioam-gre-00). One discussion topic that we decided to take to
the list was the question on whether draft-ooamdt-rtgwg-ooam-header could be
leveraged. After carefully considering draft-ooamdt-rtgwg-ooam-header, I came
to the conclusion that the “OOAM header” does not meet the needs of IOAM:
* Efficiency: IOAM adds data to live user traffic. As such, an encapsulation
needs to be as efficient as possible. The “OOAM header” is 8 bytes long. The
approach for IOAM data encapsulation in the above mentioned drafts only
requires 4 bytes. Using the OOAM header approach would add an unnecessary
overhead of 4 bytes – which is significant.
GIM>> The difference in four octets is because OOAM Header:
* provides more flexibility, e.g. Flags field and Reserved fields;
* supports larger OAM packets than iOAM header;
* is future proof by supporting versioning (Version field).
* Maturity: IOAM has several implementations, which were also shown at recent
IETF hackathons – and we’re expecting additional implementations to be
publicized soon. Interoperable implementations need timely specifications.
Despite the question being asked, the recent thread on OOAM in the NVO3 list
hasn’t revealed any implementation of the OOAM header. In addition, the thread
revealed that several fundamental questions about the OOAM header are still
open, such as whether or how active OAM mechanisms within protocols such as
Geneve would apply to the OOAM header. This ultimately means that we won’t get
to a timely specification.
GIM>> May I ask which encapsulations supported by the implementations you refer
to. Until very recently all iOAM proposals were to use meta-data TLV in, e.g.
Geneve and NSH. And if these or some of these implementations already updated
to the newly proposed iOAM shim, I don't see problem in making them use OOAM
Header. Would you agree?
* Scope: It isn’t entirely clear to which protocols the OOAM header would
ultimately apply to. The way the OOAM header is defined, OOAM uses a 8-bit
field for “Next Prot”, the next protocol. Some protocols that IOAM data needs
to be encapsulated into use 16-bits for their next protocol code points. See
e.g. the GRE encapsulation – as specified in draft-weis-ippm-ioam-gre-00.
GIM>> The first paragraph of the Introduction section states:
New protocols that support overlay networks like VxLAN-GPE
[I-D.ietf-nvo3-vxlan-gpe], GUE [I-D.ietf-nvo3-gue], Geneve
[I-D.ietf-nvo3-geneve], BIER [I-D.ietf-bier-mpls-encapsulation], and
NSH [I-D.ietf-sfc-nsh] support multi-protocol payload, e.g.
Ethernet, IPv4/IPv6, and recognize Operations, Administration, and
Maintenance (OAM) as one of distinct types. That ensures that
Overlay OAM (OOAM)packets are sharing fate with Overlay data packet
traversing the underlay.
I'm updating the OOAM Header draft and along with cleaning nits will update
reference to GUE. I think that the list and the statemnt are quite clear in
identifying the scope of networks that may benefit from using not only common
OOAM Header but common OOAM mechanisms, e.g. Echo
With the above in mind, I’d suggest that the WG moves forward with specific
definitions for encapsulating IOAM data into protocols – per the above
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