Part of my reaction to this whole section is that it looks much like the
mistake we made originally in defining classful IP addresses. You are
trying to guess the correct use cases, and defining specific address
structures with specific encodings for each one. With only a few encodings
available. This seems to be a recipe for being wrong later in ways that
hurt.
The only equivalent to classfull addressing i see is for the fixed prefix-length
handed out to each node, 1 bit (2 addresses) with zone addresses, 8/16 bits
(256/64k address) for Vlong, but its NOT assignment to network segments
as in IPv4 A/B/C but to nodes.
We didn't introduce choices lightly. There are compromises to be made when you
want some lightweight address allocation scheme, not expecting to have complex
address registry or management system in the backend but simple registrars.
see below for more
The difference in interpretation
is actually provided by the last bit in the upper 64. If these are the
same schema, then it should not need a bit to differentiate them. They
should be explained as a single schema. Which would presumably result in
the Z bit being part of the zone / subnet field. If they are two
different schemas, then move the differentiation to part of the schema
identifier (making it 3 bits).
We did not want to make Z part of the base schemas 6.10.2 "Type" code because
that would also make the Vlong scheme one bit shorter and that would reduce
virtualization space in Vlong by a factor of 2.
So, yes, encoding wise, 6.10.4 manual sub addressing space was carved out
of the 6.10.3 zone address space via the Z bit, but thats just an encoding
aspect.
Functionally, 6.10.3/6.10.4 are quite different, and therefore it is IMHO
textually correct to have them in different subsections.
Carving out bits like Z isn't ideal, but in between the ULA prefix,
the 64 bit local part we must have for external interfaces and
best utilization of bits, we tried to rather optimize address space
utilization and not beauty of encoding.
Having at the end allows (as written) use of /63 instead of 2 * /64
routes. I am not sure how important this would be in the future.
If you feel strongly about more beauty in encoding,
i can move Z to the left and remove the notion of the possible /63 route
optimization possible through the placement of Z.
Since the two different uses of the Z bit with type 00b are quite distinct,
trying to enable aggregation seems counter-productive.
While I hate to push on a point you describe as aesthetics, having the Z
bit, occuring after the Zone / subnet-ID field, but defining whether the
field is a zone or a subnet, seems awkward for insufficient reason.
I would recommend moving the Z bit up so it is after the type, and at the
front of each of the two sections reiterate that this subscheme is indicated
by the Z bit being { 0 | 1 }.
Done. (see diff).
I very much hope there is no "interesting" implementation aspect;
nothing in the current scheme that makes implemenation harder. If you
have an example that you fear, i would like to hear it.
To me, we are just defining address space allocation schemes.
I suppose likely implementations will use mask definitions that will make it
work. I pity the code reviewer.
I have read the code and tested in the lab IPv6 embedded RP adressing
and didn't feel pityfull about the job. But i weigh the overall system
complexity. Embedded-RP simplified a lot of other parts of the
multicast system at the cost of introducing an addressing scheme.
I think similarily, the ACP addressing scheme simplifies the overall system
complexity, especially registrars.
In section 6.10.5, after stating that it is not even known what the needed
usage is for more V values
Which sentence are you referring to when you say "not even known what the
needed usage is" ? I can't find it, but i would like to rectify it
if it actually is still there.
The text reads "further values use via definition in future work." In the
zone-id scheme, it is one bit. For some reason, it is 8 or 16 bits here.
Thanks, changed sentence to:
V: Virtualization bit: Values 0 and 1 are assigned in the same way as in the
Zone-ID sub-scheme.
The existing text, now directly after the list, explains examples
when a device would likely need 256 or 64k addresses:
existing text:
..."1" bit Node-Numbers are intended for ACP nodes that are ACP edge nodes ...
the document goes on to introduce the
complexity of classful nodes numbers, with the leading bit indicating how
long the node-number is. Yes, the rest of the text in that bullet tries
to
explain why you need both sizes. It seems like needless complexity that
begs for mistakes in implementation.
I was taking the example use cases we brainstormed into account, and
some of them would require a lot more addresses in the node than others,
therefore these two choices.
See my comments above. Trying to encode specific use cases into the address
format seems a problematic answer to an admittedly difficult question.
What would break if you didn't define any of this?
One could save the 2.5 bits (Type, Z) indicating the structure of the
address inside the address by encoding the designated format of the
address instead in an extension field of the ACP address information in
the certificate. We would certainly still want to have the same type
of addresses, e.g.: 2,256,64k local addresses, option for zones and
address to assign to ACP connect interfaces (manual addressing scheme)
IMHO. So, at best we could save the 2.5 bits if we wanted to keep the
functionality, which i think is all required.
I would be quite afraid of doing such a drastic change this late in
the process because i think it will take a long time to foresee the
resulting complexity introduced for registars and any other place
that now can deduct the semantic from the address and would then have
to access to what the certificate indicates in a different way (e.g.:
access to the certificate). Note that the length of the ACP information
field in the cert is also limited, so this type of extension might end
up looking even uglier to be short *sigh*.
I was always thinking that this type of more flexible option would
be a good next-step, but not a safe first step. It would make a lot
more sense after hearing implementation/deployment experiences,
especially to correctly support important options we may have
overlooked in the current schemes. Just redoing what we have differently
to save 2.5 bits isn't worth it IMHO.
Ultimately, we need to break through the chicken and egg problem
of how to build more self-managing networks. These will require
a different number of addresses inside nodes. Anything more intelligent
than address space allocations would become a complex dependency
making implementation/adoption even slower. I don't think that
offering 2, 256, 64k addresses per node is too much flexibility.
It IMHO necessary and sufficient to explore and we'll see what sticks.
Variation is needed. That was true of allocations in IP. encoding the
variations proved a bad choice.
Let me repeat that we are not doing any network/subnet prefix encoding which is
what IPv4 A/B/C was. And there are IMHO good examples how encoding in IPv6
did save the day from complexity (at least all the stuff done for IPv6
multicast, ASM/SSM, zones, Embedded-RP) was highly useful.
In section 6.11.1.11 in describing the prefix lengths, I thought that the
point of zone addressing was to allow the use of /64 prefixes. But it
seems here that we will not do so ?
As mentioned above: This document does not describe the routing setup for /64
(or /63 with Z-bit) routing aggregation. There are multiple options,
but we could not conclude on a single solution that we felt to be
appropriate for this document. Instead it was only very important
to carve out addressing space to support this.
The net effect seems to be to prohibt the very things that you went to a lot
of trouble to enable in your addressing design.
Maybe i do not understand your comment correctly, but i do not
think it is correct. We just have not defined recommended mechanisms
how to set up routing to use /64 zone routes. That is something IMHO
better done in a followup document because all the cases where we
did see a need for znes where really very specific to particular
deployment styles and would not be applicable to the mayority of ACPs.
Nevertheless, we felt those cases where important enough to reserve
bits for them through the zone field.
...
*** Section 10.3.2 paragraph 2 says that devices should change the meaning
of "admin down" to mean "down for everything except ACP / Anima". I can
understand why, in an autonomic network, such a state is desirable. However,
that really should be a different state from "admin down". Operators already
understand "admin down" as meaning that this interface will not be used for any
traffic. Changing that is fairly drastic. "admin limited" or "admin ACP-Only"
would seem much better than changing the meaning of "admin down". The
justification in the text seems to be a desire to prevent an operator from
doing what he intends. that seems backwards. (Note that the distinction
between administrative state vs operational state, aka failed, is already well
understood.)
Well, this is in an informative section, so hopefully something we can agree to
disagree.
If this were truly informative, it would not belong in this document at all.
Changing the behavior of widely understood configuration behaviors is NOT a
small thing. Changing the permissions models for widely understood
configuration operations is also NOT a small thing.
My suggestion is that you remove all of this material. If you feel it is
important, write an I-D for standards track on evolving the configuration
model for robust ANIMA. While I think the change is a mistake, you clearly
have the right to cause the discussion.
Hiding the topic in an "informational" note in the ACP document seems VERY
wrong.
Also note that in your discussion below, you talk about the equivalence of
admin down and physical down. Most management models I know of treat these
as quite distinct. SO that is at best a red herring.
Hmm. I really only CLI derived from Cisco IOS, and there the
interface level "shutdown" command doubles IMHO both as admin down and
as phy down, so i would contend that this is a red herring. It actually
does show up in diagnostic CLI as "admin down", but is also bringing down
phy state. Therefore it is also used to diagnose phy, .e.g: shutting down
one side of a supposed direct p2p link to verify the phy change on the
other side. That practical experience is what the text and direction is
based on.
Whats an example where admin/phy down are separate in your experience ?
I don't know how you define "truly informative". I simply meant
informational as compared to standards track wrt. to not impacting
interoperability, but also as a precursor work to give opportunity
for gaining more experience before attempting to go standard.
If/when i find time i definitely would like to investigate how this
could be formalized through a YANG model for ACP so that it can become standard,
but i definitely agree that especially this part of the YANG model would
be highly difficult to get to before any experience is gained with
this.
I therefore would very much hesitate removing this text from the document, it
was
specifically asked for several times in the working group to understand
how the promised reliability of the ACP against operator/contoller
operation could be achieved. Having this in a first round (this document)
as "informational" is IMHO a good and important thing.
(text retained for context of further discussions.)
I strongly believe that the most easy way to operationalize the ACP and
achieve its goals is what we have written.
The historic equivalence of "down" = "admin down" = "physical down" is one of
the the most fundamental problem of remote management in networks.
We really need to start thinking of separate layers of (remote) management.
Network services on one hand and physical infra on the other.
The first thing to do this is to separate operations such as "down"
into "admin down" that affects networks services and "phy down" that
affects the physcial infra.
If you have existing commands like "shutdown" that today do both,
the safe mapping is to let them do the safe thing in the future, e.g:
only "admin down", and introduce new commands for the phy operations,
e.g.: "phy shutdown" or the like.
And then protect those dangerous commands even further against unintentional or
intentional misuse.
Think of ACP/ANI also as a seamless inband version of a DCN. As an operator
of the actual data network, you also didn't have any access to bring down the
DCN
and cut yourself off from the network you manage. YOu could only screw
up that network you're meant to manage.
And if your network consists of VMs in a DC, a "shutdown" on their
interfaces will also not bring down physical interfaces necessary
to reach the VM.
In optical networks you often have an inband physcial ethernet management
channel. Making/breaking that one is completely different from making/breaking
your data-plane, aka: data fiber colors.
*** The notion in 10.3.6 that the device should refuse to disable
functionality when an authorized administrator directs such seems flatly wrong.
The authorization to break your own remote management connectivity
would be a property of the certificate. clearly whoever enrolled
the device with a certificate denying that capaility to the operator
did NOT authorize the administrator to break connectivity.
The security model change seems as problematic as the above configuration
change.
We have recurringly heard from customers that mistakes in managing remote
equipment and loosing connectivity is a mayor pain point. Creating
an operational option that limits/disables operators ability to
impact phy level connectivity that remote management depends upon and therefore
reducing this risk and cost factor seems to me like a very logical pah
forward. Whether or not this should be indicated in the certificate
or differently is definitely wide open.
I agree that none of these operational interface level changes are
a piece of cake given how we have in the IETF not tried to define
different access levels to configuration so far, at least not
between some phy/infra access level and network-services access level.
As said above in my first reply that you didn't comment on, i think a
good part of what i am looking for may happen through other means
already, such as when a router is just a VM running on an OS. At least
in early versions of this that i'd seen, this implicitly disabled
the ability to modify phy state from the router VM, and of course
complaints where raised that phy mods where necessary, but at least this
evolution could give raise to pause and rethink HOW to permit doing this.
So i would at least like to pledge with you that it is a good thing to
have this type of discussion in an informational way in this RFC instead
of doing nothing or trying to go standard YANG directly as a first step.
It did get into the spec because of the desire of the working group.
Editorial / Nits:
.
In the various formats in section 6.10, the lowest bit of the upper 64
bits
is mandated to be 0. Presumably, there is some reason for doing this. It
would be nice to explain it.
Sorry, not clear what you're referring to. Can you give me an
explicit reference ?
I should ahve removed this note. It was a side-effect of the presentation
and ordering, not a problem on its own. Sorry.
Cheers
Toerless
