Hi authors, chairs, WG,
I’m generally supportive of this work, but I think that there are still some
potential corner cases that are not covered, or it isn’t entirely obvious how
they are handled.
Comments below.
Moderate level comments:
(1) p 7, sec 2.3. Inactive-Until-Referenced
There are some system configuration predefined (e.g., application
ids, anti-x signatures, trust anchor certs, etc.) as a convenience
for the clients, which must be referenced to be active. The clients
can also define their own configurations for their unique
requirements. Inactive-until-referenced system configuration is
generated in <system> immediately when the device is powered on, but
it is not active until being referenced.
I'm not sure whether Inactive-Until-Referenced actually needs to be defined, or
to put it another way, I'm not sure whether this type of configuration is
special to system datastores at all. If a configuration (either explicitly in
<running> or implicitly from <system>) defines a QoS policy that is not
referenced from anywhere, (e.g., not applied to any interfaces) then I think
that it up to the server to decide whether that unreferenced QoS policy is
reported in operational or not, depending on server implementation.
(2) p 9, sec 5.1. Conceptual Model of Datastores
When the device is powered on, immediately-active system
configuration is generated in <system> and active immediately, but
inactive-until-referenced system configuration only becomes active if
referenced by client-defined configuration. However, conditionally-
active system configuration will only be created and active when
specific conditions on system resources are met.
I think that it should be "merged with system" not "merged into system" since
the running configuration never ends up in the system datastore.
(3) p 9, sec 5.1. Conceptual Model of Datastores
additional nodes to a list entry or new list/leaf-
list entries appearing in <running> extends the list entry or the
whole list/leaf-list defined in <system> if the server allows the
list/leaf-list to be updated.
How is this achieved? This appears to suggest that there are two different
merging behaviours (one choice is to be additive, the other is to replace), and
it seems to be down to the server to choose what to do on a case-by-case basis.
I think that it would be cleaner to define a single merge behaviour if that is
feasible (even if it is slightly less flexible). Also, potentially it is
appropriate for the merge behaviour to be different for list vs leaf-list
(e.g., always merge list entries, but do a simple replace on leaf-lists).
(4) p 9, sec 5.1. Conceptual Model of Datastores
If a server implements
<intended>, <system> MUST be merged into <intended>.
This sentence is just repetition and can be deleted. The text above is still
normative without the RFC 2119 MUST.
(5) p 13, sec 5.4. Modifying (Overriding) System Configuration
For instance, descendant nodes in a system-defined list entry may be
modifiable or not, even if some system configuration has been copied
into <running> earlier. If a system node is non-modifiable, then
writing a different value for that node MUST return an error. The
immutability of system configuration is defined in
[I-D.ma-netmod-immutable-flag].
I think that some care is needed here. E.g., if the modification was being
done to <candidate>, then it isn't writing a different value to <candidate>
that would return an error, but instead the <validate> or <commit> operation
that would fail.
(6) p 13, sec 5.4. Modifying (Overriding) System Configuration
A server may also allow a client to add data nodes to a list entry in
<system> by writing those additional nodes in <running>. Those
additional data nodes may not exist in <system> (i.e., an *addition*
rather than an override).
Earlier, the text in 5.1 seems to suggest that a list-entry could be
overwritten. Is the intention that this is always a merge? I.e., it is
possible to override entries, but there is no way that running can remove a
list entry that is defined in <system>.
This section, 5.4., seems somewhat of a repeat of what is specified in section
5.1, and arguably it would be nice if this text could be co-located and only
specified once (for brevity and to avoid ambiguity). I’m wondering if the
merge behaviour generally needs to be specified more explicitly.
Minor level comments:
(7) p 0, sec
This document defines how a management client and server handle YANG-
modeled configuration data that is defined by the server itself. The
system-defined configuration can be referenced (e.g. leafref) by
configuration explicitly created by a client.
Perhaps 'instantiated' by the server itself rather than 'defined' by the server.
(8) p 0, sec
The Network Management Datastore Architecture (NMDA) defined in RFC
8342 is updated with a read-only conventional configuration datastore
called "system" to hold system-defined configuration.
Perhaps 'expose system-defined configuration' to clients rather than 'hold'.
(9) p 0, sec
As an alternative to clients explicitly copying referenced system-
defined configuration into the target configuration datastore (e.g.,
<running>) so that the datastore is valid, a "resolve-system"
parameter is defined to allow the server acting as a "system client"
to copy referenced system nodes automatically. This solution enables
clients manipulating the target configuration datastore (e.g.,
<running>) to reference nodes defined in <system>, override system-
provided values, and configure descendant nodes of system-defined
configuration.
I think that this paragraph is too detailed to be in the abstract and should be
removed from the abstract.
(10) p 4, sec 1.1. Terminology
The following terms are defined in this document:
System configuration: Configuration that is provided by the system
itself. System configuration is present in the system
configuration datastore (regardless of whether it is applied or
referenced) and appears in <intended> unless explicitly
overridden. System configuration that is considered active
appears in <operational> with origin="system". It is a different
and separate concept from factory default configuration defined in
RFC 8808 (which represents a preset initial configuration that is
used to initialize the configuration of a server).
RFC 8808 should turn into a proper reference, it looks like it is just text
here.
(11) p 5, sec 1.4. Updates to RFC 6241 and RFC 8526
This document defines a NETCONF protocol capability to indicate
support for this parameter. NETCONF server that supports "resolve-
system" parameter MUST advertise the following capability identifier:
Are we ambiguous as to whether this must be supported, or is optional to
implement? Ah, I see that this is specified later in the document (which is
arguably the right place). Is the capability really an update to RFC 6241 and
8526? I wonder whether this last paragraph (i.e., the capability definition)
would be better under section 5.3.
(12) p 5, sec 1.5. Updates to RFC 8040
This document extends Sections 4.8 and 9.1.1 of [RFC8040] to add a
new query parameter "resolve-system" and corresponding query
parameter capability URI.
Again, I think that possibly sections 1.5.1 and 1.5.2 would be better outside
of the introduction, perhaps as subsections of 5.3. Then section 1.5, could
then forward reference to those sections.
(13) p 6, sec 2. Kinds of System Configuration
Active system configuration refers to system configuration that is
currently in use. As per definition of the operational state
datastore in [RFC8342], if system configuration is inactive, it does
not appear in <operational>. However, system configuration is
present in <system> once it is generated, regardless of whether it is
active or not.
I'm not sure that calling this "active configuration" is a great choice,
because it seems to be a slightly different concept to inactive configuration
defined in RFC 8342. Specifically, I thought that the inactive configuration
in RFC 8342 controlled whether or not it would appear in <intended>, but in
this case, presumably it always turns up in <intended> if it is in <system> and
instead doesn't appear in <operational>?
(15) p 7, sec 3. The System Configuration Datastore (<system>)
* Management operations: The content of the datastore is set by the
server in an implementation dependent manner. The content can not
be changed by management operations via protocols such as NETCONF,
RESTCONF, but may change itself by license change, device upgrade
and/or system-controlled resources change. The datastore can be
read using the standard network management protocols such as
NETCONF and RESCTCONF.
Rather than saying that the contents can change itself, I think that it would
be better to say that the server may change the contents under various
conditions, such as ...
(16) p 7, sec 3. The System Configuration Datastore (<system>)
* Origin: This document does not define any new origin identity when
it interacts with <intended> and flows into <operational>. The
"system" origin Metadata Annotation [RFC7952] is used to indicate
the origin of a data item is system, which is achieved by updating
the definition of "intended" origin metadata annotation in
[RFC8342].
If a different value is configured in <running> that overrides a value in
<system> then it is clear that the origin should be <intended>. Do we specify
what the origin should be if the same value exists in both <running> and
<system> (which could be a very common occurrence if resolve-system is used)?
(17) p 8, sec 3. The System Configuration Datastore (<system>)
The system datastore is defined as a conventional configuration
datastore and shares a common datastore schema with other
conventional datastores.
This paragraph should probably move up to "YANG modules".
(18) p 8, sec 4.2. May Change via Software Upgrades or Resource Changes
* Servers rejects the operation to change system configuration
(e.g., device upgrade fails) and needs the client to correct the
configuration in <running> as a prerequisite to ensure validity
Should we add a recommendation for servers to document how they handle these
issues?
(19) p 10, sec 5.1. Conceptual Model of Datastores
ct = config true; cf = config false
rw = read-write; ro = read-only
boxes denote named datastores
In this diagram, (1) please move the system box 1 line to the left to keep is
more cleanly separate from the arrow into running. (2) I think that we should
discuss whether the running and system arrows should merge at a common point
rather than running flowing into the side.
(20) p 10, sec 5.1. Conceptual Model of Datastores
ct = config true; cf = config false
rw = read-write; ro = read-only
boxes denote named datastores
I know that it isn't directly related to this work, but I wonder whether the
"default configuration" arrow is really in the right place, and whether that
shouldn't also be feeding this arrow into <intended>, since validation would
surely take default values into account. But this is perhaps a question for
another day ...
(21) p 11, sec 5.1. Conceptual Model of Datastores
Any deletable system-provided configuration that is populated as part
of <running> by the system at boot up, without being part of the
contents of a <startup> datastore, must be defined in <factory-
default> [RFC8808], which is used to initialize <running> when the
device is first-time powered on or reset to its factory default
condition.
I agree with the sentiment of what is written here, but I'm not sure that it is
wise to restate it in this document, or whether it would be better to delete
this paragraph and just reference RFC 8808.
E.g., maybe something like ..
<factory-default> [RFC8808] defines a mechanism for populating <running> at
system boot up with regular configuration data nodes, that hence can be deleted.
(22) p 12, sec 5.3. Servers Auto-configuring Referenced System Configuration
("resolve-system" parameter)
The "resolve-system" parameter is optional and has no value. If it
is present, and the server supports this capability, the server MUST
copy referenced system nodes into the target datastore (e.g.,
<running>) without the client doing the copy/paste explicitly, to
resolve any references not resolved by the client. The server acting
as a "system client" like any other remote clients copies the
referenced system-defined nodes when triggered by the "resolve-
system" parameter. Legacy clients interacting with servers that
support this parameter don't see any changes in <edit- config>/<edit-
data> and <copy-config> behaviors.
How does resolve-system interplay with the candidate configuration datastore?
E.g., should it also be listed in the examples of datastores. What about the
<validate> or <commit> operations? Is there any impact of private-candidate
datastores, and if so, where should that be documented?
(23) p 12, sec 5.3. Servers Auto-configuring Referenced System Configuration
("resolve-system" parameter)
The server's copy referenced nodes from <system> to the target
datastore MUST be enforced at the end of the <edit-config>/<edit-
data> or <copy-config> operations during the validation processing,
regardless of which target datastore it is.
This probably means that it isn't a separate "system client" because I would
expect that to turn in the commit history as a separate commit, but instead,
the update to running via resolve-system is exactly the same as if the client
had made the modification directly as part of an edit-data (or similar)
operation.
(24) p 13, sec 5.3. Servers Auto-configuring Referenced System Configuration
("resolve-system" parameter)
If the "resolve-system" parameter is not given by the client, the
server should not modify <running> in any way otherwise not specified
by the client. Not using capitalized "SHOULD NOT" in the previous
sentence is intentional. The intention is to bring awareness to the
general need to not surprise clients with unexpected changes. It is
desirable for clients to always opt into using mechanisms having
server-side changes. This document enables a client to opt into this
behavior using the "resolve-system" parameter. An example of this
type of opt-in behavior can also be found in RFC 7317, which enables
a client to opt into its behavior using a "$0$" prefix (see
ianach:crypt-hash type defined in [RFC7317]).
Arguably, I don't think that above paragraph is needed at all and can just be
removed. Otherwise, you could argue that it perhaps conflicts with the text in
4.2?
(25) p 13, sec 5.3. Servers Auto-configuring Referenced System Configuration
("resolve-system" parameter)
Implementation specifics are beyond the scope of this document,
however, due to the extra complexity brought by the "resolve-system"
parameter, clients should be aware that it would cost a reasonable
amount of time for the server to resolve reference, retrieve and copy
the referenced system configuration from <system>, which could take
multiple rounds since some errors may depend on the resolution of
previous ones.
Suggest changing "it would cost" to "it may take". But I'm also not really
sure that this paragraph should be in the document (e.g., what is a reasonable
amount of time? Is it 1 second, or a minute, or a few minutes).
(26) p 24, sec 6.2. Example Usage
The local port and remote port are used when the BGP peer connection
is established. Since both are not supplied explicitly in <running>
and <intended>, the default value for "bgp/peer/remote-port" is used,
and there is no default statement for "bgp/peer/local-port", the
system will select a value for it. So the contents of <system> are
shown as follows:
There is some level of interplay here between YANG default values and the
information present in system. E.g., depending on how the YANG data model is
written (i.e., sometimes complex default values are specifying in description
statements rather than as formal YANG defaults), then the choice as to whether
to report a value in system vs a default value in the configuration may be a
bit ambiguous. E.g., this example of using the local-port as an example of
system configuration potentially feels like the weakest of the alternative
justifications that have been provided.
(27) p 29, sec 7.3. YANG Module
description
"When present, the server is allowed to automatically
configure referenced system configuration into the
target configuration datastore.";
Should this be "is allowed to automatically configure", or should it be "must
automatically configure"?
(28) p 31, sec 9.2. Regarding the "ietf-netconf-resolve-system" YANG Module
The security considerations for the base NETCONF protocol operations
(see Section 9 of [RFC6241] apply to the new extended RPC operations
defined in this document.
Possibly, this section should say a bit more about the security impacts of
supporting the resolve-system option, i.e., that there aren't any beyond the
potential performance impacts of implementing resolve-system, which may mean
that employing some form of rate limiting of requests specifying this option
might be a good idea to avoid DoS attacks.
(29) p 35, sec Appendix A. Key Use Cases
A.1. Device Powers On
Please provide a short prose description of what the example illustrates.
(30) p 35, sec Appendix A. Key Use Cases
<running>:
Please expand these, e.g. The <running> datastore contains:
(31) p 35, sec Appendix A. Key Use Cases
<system>:
Please expand these, e.g. The <system> datastore contains:
(32) p 35, sec Appendix A. Key Use Cases
<intended>:
Please expand these, e.g. After merging,the <intended> datastore contains:
(33) p 35, sec Appendix A. Key Use Cases
<operational>:
Please expand these, e.g. Once the configuration is applied, the <operational>
datastore contains:
(34) p 36, sec Appendix A. Key Use Cases
<running>:
Please expand these simiarly to above for the other examples, A.2 and A.3.
(35) p 36, sec Appendix A. Key Use Cases
<interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
or:origin="or:intended">
As per a previous comment, I wonder whether the origin of the 'interfaces'
container itself should be 'intended' or 'system' (given than loopback always
exists and hence it can never be removed).
(36) p 37, sec Appendix A. Key Use Cases
<interface or:origin="or:system">
<name>lo0</name>
<ip-address>127.0.0.1</ip-address>
<ip-address>::1</ip-address>
</interface>
</interfaces>
A.3. Operator Installs Card into a Chassis
Please provide a short prose description of what the example illustrates.
Nit level comments:
(37) p 5, sec 1.3. Updates to RFC 8342
Configuration in <running> is merged into <system> to create the
contents of <intended> after the configuration transformations to
<running> (e.g., template expansion, removal of inactive
configuration defined in [RFC8342]) have been performed. This
document updates the definition of "intended" origin metadata
annotation identity to allow a subset of configuration provided by
<intended> to use "system" as origin value as it flows into
<operational>. Applied system configuration appears in <operational>
with origin value being reported as "system" (Section 5.1).
I think that "<running> is merged into <system>" is confusing. I would say
that <running> is merged with the contents of <system> and how that merge is
performed must be specified.
(38) p 8, sec 3. The System Configuration Datastore (<system>)
* Defining YANG module: "ietf-system-datastore".
The datastore's content is defined by the server and read-only to
clients. Upon the content is created or changed, it will be merged
into <intended>. Unlike <factory-default> [RFC8808], it MAY change
dynamically, e.g., depending on factors like license change, device
upgrade or system-controlled resources change (e.g., HW available).
The system configuration datastore doesn't persist across reboots;
<factory-reset> RPC operation defined in [RFC8808] can reset it to
its factory default configuration without including configuration
generated due to the system update or client-enabled functionality.
Upon the content => When the content. Some of the content here seems to repeat
the text in "Management operations", I think the examples would be better in
only a single place.
(39) p 8, sec 4.2. May Change via Software Upgrades or Resource Changes
If system configuration changes (e.g., due to device upgrade),
<running> MAY become invalid. The server behaviors of migrating
updated system data into <running> is beyond the scope of this
document. That said, the following gives a list of examples of
server implementations that might be possible:
Suggest rewording to: "That said, here are some examples of how a server might
handle this scenario:"
(40) p 9, sec 4.3. No Impact to <operational>
This work intends to have no impact to <operational>. System
configuration appears in <operational> with origin value being
reported as "system" if not configured or overridden explicitly in
<running>. This document enables a subset of those system generated
nodes to be defined like configuration, i.e., made visible to clients
in order for being referenced or configurable prior to present in
<operational>. "Config false" nodes are out of scope, hence existing
"config false" nodes are not impacted by this work.
As per above, does "Overridden explicitly" mean "has a different value" in
running?
(41) p 12, sec 5.3. Servers Auto-configuring Referenced System Configuration
("resolve-system" parameter)
Note that even an auto-configured node is allowed to be deleted from
the target datastore by the client, the system may automatically
configure the deleted node again to make configuration valid, when a
"resolve-system" parameter is carried. It is also possible that the
operation request (e.g., <edit-config>) may not succeed due to
incomplete referential integrity.
Perhaps "recreate the deleted node" rather than "configure the deleted node".
(42) p 12, sec 5.3. Servers Auto-configuring Referenced System Configuration
("resolve-system" parameter)
Support for the "resolve-system" parameter is OPTIONAL. Servers not
supporting NMDA [RFC8342] MAY also implement this parameter without
implementing the system configuration datastore, which would only
eliminate the ability to expose the system configuration via protocol
operations. If a server implements <system>, referenced system
configuration is copied from <system> into the target datastore
(e.g., <running>) when the "resolve-system" parameter is used;
otherwise it is an implementation decision where to copy referenced
system configuration into the target datastore (e.g., <running>).
Perhaps 'examine' rather than 'expose'.
(43) p 21, sec 5.5.3. Modifying a System-instantiated Leaf's Value
<interfaces xmlns="urn:example:interface">
<interface>
<name>lo0</name>
<mtu>65536</mtu>
<ip-address>127.0.0.1</ip-address>
<ip-address>::1</ip-address>
</interface>
</interfaces>
A client modifies the value of MTU to 65535 and adds the following
configuration into <running>:
I initially hadn't spotted the subtle change, perhaps use an MTU value that is
more obviosuly different from the value in system. E.g., perhaps 9216.
Regards,
Rob
From: netmod <netmod-boun...@ietf.org> on behalf of Kent Watsen
<kent+i...@watsen.net>
Date: Friday, 29 March 2024 at 14:09
To: netmod@ietf.org <netmod@ietf.org>
Subject: [netmod] WGLC on system-config-05
This email begins a two-week WGLC on:
System-defined Configuration
https://datatracker.ietf.org/doc/draft-ietf-netmod-system-config/
Please take time to review this draft and post comments by April 12. Favorable
comments are especially welcomed.
There is no known IPR for this document:
https://mailarchive.ietf.org/arch/msg/netmod/IpzWIAbgifXoKaNfLhEDmYbyXkY/
Kent // co-chair
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