Dear Susan Hares,
I deeply appreciate for your kind explanation about the multi-headed
control of I2RS so that I reviewed the architecture document again and
understood about the error-handling mechanism and the simplicity of I2RS
nature. Sorry for my poor understanding of I2RS.
Regarding to your comments, I still have some questions to be more clear.
First, as you explained and the architecture states, the manipulation of
the collision of multi-headed control can be processed by the assignment
of client priorities.
Rather, when the priority ties, the first client can keep the control.
At this point, the first client means the firstly connected client for
the controlling data or firstly connected client to the agent with that
data?
Second, the statements of two documents, architecture
(draft-ietf-i2rs-architecture-00) and protocol
requirement(draft-rfernando-i2rs-protocol-requirements-00), seem to have
somewhat different views about the communication channel between client
and agent. In the architecture document, Sec 6.2 states the
communication channel between client and agent does not need to keep
continuous transport. But Sec 4.2 TR-12 of the protocol requirement
document states that keep-alives at transport level or I2RS protocol
level could be provided for detecting the session failure. And
simulataneous usage of session and communication channel of the
architecture document is confusing for me.
Finally, I have a question about the network application and client for
client redundancy. I think client is not equal to network application.
The architecture document states in Sec 6.5 for handling dead clients
"the network applications or management systems will detect a dead
network application and either restart that network application or clean
up any state left behind." In addition, for basic client redundancy, the
architecture states active and backup network application can be used.
At this point, I want to know both network applications are physically
separated from the client?
Thank you for your comments, again :-)
best regards,
Kwang-koog Lee (KT)
On Fri, Jan 17, 2014 at 5:55 PM, Songhaibin (A) <haibin.s...@huawei.com
<mailto:haibin.s...@huawei.com>> wrote:
Hi Sue,
Thank you very much for so detailed explanation. I understand your
two principles very clearly now.
What comes into my mind is the following use case. Let's say it a
bandwidth on demand scenario. Two clients A and B have different
priorities to change user X's access bandwidth, and one client could
be embedded in the user itself while another client is the system
admin. Client A has higher priority. Then user X's access bandwidth
is the piece of data. At time Y, Client A requests to change X's
bandwidth to 20Mbps for two hours. And after two hours, X's
bandwidth is reset to its default value. And after the time Y+2,
either A or B should have the permission to change X's bandwidth data.
I guess you probably have already considered this.
Best Regards!
-Haibin
> -----Original Message-----
> From: Susan Hares [mailto:sha...@ndzh.com <mailto:sha...@ndzh.com>]
> Sent: Friday, January 17, 2014 7:47 AM
> To: 'Joel M. Halpern'; Songhaibin (A); 'KwangKoog Lee'
> Cc: i2rs@ietf.org <mailto:i2rs@ietf.org>; Guanxiaoran
> Subject: RE: [i2rs] Multi-Headed Control
>
> Mach, Haibin, and KwanKooq:
>
> Joel gave you brief answers and then suggested reading the
document. As
> one of the co-authors, I will attempt to give the "longer"
answers. I hope this
> will encourage discussion sections in the architecture document.
>
> This is not suggest current flaws in the architecture draft, but
to elucidate
> (explain in depth) some of the drafts concepts. You may be
asking questions
> that we hope will be discussed on the list, but I cannot tell yet.
> There are many sections in the architecture draft end with the
phrase "Editor's
> note: This topic (or These topics) need more discussion in the
working group."
> We encourage discussion of these drafts.
>
> If I am not answering the question, please just tell me. The
important part of
> this work is to get an architecture and drafts that can be
implemented in
> routers and switches.
>
> Ok.. enough introduction. On to a longer review that ends in a
question:
>
> Review:
> ---------
>
> In section 1.2, page 6 (bottom) of the -00 version of the
architecture draft, I
> states:
>
> " As can be seen in Figure 1, an I2RS client can communicate with
> multiple I2RS agents. An I2RS client may connect to one or
more I2RS
> agents based upon its needs. Similarly, an I2RS agent may
> communicate with multiple I2RS clients - whether to respond to
their
> requests, to send notifications, etc. Timely notifications are
> critical so that several simultaneously operating applications
have
> up-to-date information on the state of the network."
>
> Note here that the architecture states you may have one agent
talking to
> multiple I2RS clients. Once you enter this zone, you can have
collisions.
> In the beginning , we talk and talked about ways that you could
handle
> collisions - but we want to start simple.
>
> The phrase "protocol parsimony is clearly a goal" (section 3.1,
p. 9) suggest we
> are trying to implement just a few things in the first version of
I2RS Clients and
> I2RS Agents. From there, the I2RS protocol will be extended later.
>
> The simple rule for multi-headed control (section 6.8) is to
consider that two
> clients manipulating the same piece of data is an error. For example,
> configuring an static route of prefix 192.1.1.0/24
<http://192.1.1.0/24> should only be done by one
> client. If two I2RS clients try to change the same piece of data
in the same
> I2RS Agent, it is an error.
>
> The architecture then requires that the I2RS clients and Agents
have a
> decidable way for the Agent to resolve the error. Section 6.8
states our
> simple way:
> 1) assign each client a priority (either by policy or default policy)
> 2) If the priorities tie, the first client "whose attribution is
associated with the
> data" keeps the control.
>
> That means - if you tie is First-come-keeps-control (FCKC)
>
> This is important to consider when you look at data models, scope
(Section 2, p.
> 7-8), and identity. You will note that the RIB manager is the
easiest thing to
> start with. Only one person can change one prefix, but multiple
I2RS clients
> can add different prefixes to the list.
>
> Now, what if I2RS client A wants to add 10 prefixes to the RIB
and this includes
> 192.1.1.0/24 <http://192.1.1.0/24> to a single I2RS agent and
I2RS client B wants to add
> 1 prefix 192.1.1.0/24 <http://192.1.1.0/24>. Does it cause a
problem with I2RS client A if I24S
> Client B gets there first (FCKC), and only 9 prefixes get added.
>
> That very issue is what section 6.9 deals with.
>
> Questions:
> -----------
> 1. Are you trying to determine what happens when the multi-headed
control
> hits one of these errors? [See Sections 6.5, 6.6, 6.8 and 6.9]
>
> 2. Are you trying to build redundant clients (I2RS client A and
I2RS Client
> A') which are redundant clients? [See section 6.4.1]
>
> 3. Are you concerned about multi-headed control with multiple
interfaces per
> client?
> (You could have 4 SCTP and 4 TCP session over which this
protocol runs)
> [Section 6.2]
>
> 4. How does a I2RS client A that reads the data know when I2RS
Client B
> modifies the Data?
> [Section 6.8]
>
> Sue Hares
>
>
>
> -----Original Message-----
> From: i2rs [mailto:i2rs-boun...@ietf.org
<mailto:i2rs-boun...@ietf.org>] On Behalf Of Joel M. Halpern
> Sent: Tuesday, January 14, 2014 11:11 PM
> To: Songhaibin (A); KwangKoog Lee
> Cc: i2rs@ietf.org <mailto:i2rs@ietf.org>; Guanxiaoran
> Subject: Re: [i2rs] Multi-Headed Control
>
> There are no locks.
> The changes made by the higher priority client remain in effect
until either they
> are removed by that client or an even higher priority client
erroneously
> over-writes them. Changes do not have lifetimes.
>
> One of the points of this mechanism was to avoid needing to guess
what order
> things happened in if they are close in time and you want to know
the results.
>
> Please, read the draft.
>
> Yours,
> Joel
>
> On 1/14/14 10:50 PM, Songhaibin (A) wrote:
> > Hi Joel,
> >
> > It is a little confusing for me. See inline.
> >
> >> -----Original Message-----
> >> From: i2rs [mailto:i2rs-boun...@ietf.org
<mailto:i2rs-boun...@ietf.org>] On Behalf Of Joel M.
> >> Halpern
> >> Sent: Tuesday, January 14, 2014 11:43 PM
> >> To: KwangKoog Lee
> >> Cc: i2rs@ietf.org <mailto:i2rs@ietf.org>; Guanxiaoran
> >> Subject: Re: [i2rs] Multi-Headed Control
> >>
> >> While I will try to paraphrase things to answer your question, I
> >> recommend you read the archtiecture draft to get more details.
> >>
> >> The assumption is that normally different I2RS clients will be
asking
> >> the agent to perform operations which change different pieces
of data.
> >> We discussed various models of conflict resolution for the
case when
> >> one client adjusts a piece of data, and then another client
goes to
> >> change that data. We decided that this was an error, and that we
> >> wanted a simple mechanism to decide what to do, while the clients
> >> sort
> out what was intended.
> >
> > Except for client priorities, there are other factors like
timing. I
> assume that a client with higher priority changes a piece of
data, but then a
> client with lower priority can make changes to the same piece of
data. It could
> possibly depend on the how long the client with higher priority
wants that
> change to take effect.
> >
> > But when two clients want to make changes to the same data at
the same
> time, then the client with higher priority will get the <lock>,
and the request
> from the client with lower priority will be denied. And we can
leave the choice
> on whether to make another try to the client itself.
> >
> > Regards!
> > -Haibin
> >
> >> Rather than
> >> pure FCFS, we decided to have client priorities. And that clients
> >> could arrange
> >> (easily) to be notified of changes to data they are interested in.
> >>
> >> The goal is to keep the mechanisms very lightweight,
particularly in
> >> order to support very high rates of operations.
> >>
> >> Yours,
> >> Joel
> >>
> >> On 1/14/14 10:29 AM, KwangKoog Lee wrote:
> >>> I do not fully understand the data model of i2rs. But in case
that
> >>> many clients interact forwarding devices with the i2rs-enabled
> >>> control plane, various policies about routing, signaling, qos and
> >>> etc. from multiple clients or multiple upper users (network
> >>> applications) can be set to those devices and to prevent or
> >>> negotiate some collision of multiple policies, such a machanism
> >>> might be necessary regardless of
> >> netconf?
> >>> Joel or anyone can explain more why it does not need?
Thanks in
> advance.
> >>>
> >>> best regards,
> >>> Kwang-koog Lee
> >>> On Tue, Jan 14, 2014 at 11:19 PM, Joel M. Halpern
> >>> <j...@joelhalpern.com <mailto:j...@joelhalpern.com>
<mailto:j...@joelhalpern.com <mailto:j...@joelhalpern.com>>> wrote:
> >>>
> >>> As I read the documents, locking is specifically not the
approach
> >>> I2RS is taking. So I think that "<lock>" does not
suffice to
> >>> resolve the I2RS needs, and is in fact not part of the
current I2RS
> >>> arhtiecture at all.
> >>> Yours,
> >>> Joel
> >>> On 1/14/14 4:17 AM, Guanxiaoran wrote:
> >>>
> >>> Hi,
> >>> I've a question about i2rs multi-headed control and
NETCONF.
> >>> [draft-ietf-i2rs-problem-__statement-00]
describes:"Additional
> >>> extensions to handle multi-headed control may need to be
> added
> >>> to NetConf and/or appropriate data models."
> >>> [draft-ietf-i2rs-architecture-__00] describes:"The
current
> >>> recommendation is to have a simple priority
associated with
> each
> >>> I2RS clients, and the highest priority change remains in
> effect."
> >>> As NETCONF has <lock> mechanism: "The <lock> operation
> allows
> >>> the client to lock the entire configuration data-store
> >>> system
> of
> >>> a device. Such locks are intended to be short-lived
and allow a
> >>> client to make a change without fear of interaction
with other
> >>> NETCONF clients, non-NETCONF clients (e.g., SNMP and
CLI),
> and
> >>> human users."
> >>> Do we still need to do the extensions, i.e. additional
> >>> extensions to handle multi-headed control added to
NETCONF?
> >>> Regards,
> >>> Ran
> >>> _________________________________________________
> >>> i2rs mailing list
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<mailto:i2rs@ietf.org>>
> >>> https://www.ietf.org/mailman/__listinfo/i2rs
> >>> <https://www.ietf.org/mailman/listinfo/i2rs>
> >>>
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> >>>
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