Hi Vladimir,
First point of clarification is that this is not about running/intended
at all. The contents of running/intended do not change in anyway
depending on whether hardware is present or absent.
The section is only concerned with how the configuration is applied in
operational, and basically says that you cannot apply configuration for
resources that are missing (which seems reasonable). E.g. I cannot
configure an IP address on a physical interface that isn't there. Or if
the physical interface gets removed then the configuration associated
with that interface is also removed from operational.
Operational isn't validated and data model constraints are allowed to be
broken (ideally transiently). But I agree that there could be
configuration that is referencing those missing resources, and depending
on implementation then that configuration may need to become not applied
as well. Or perhaps the failure is reported in a different way (e.g.
IGP neighbor is down).
I also agree that this is non trivial, but the systems that I am
familiar with have always had to deal with this issue. At the data
model level I don't think that this is any more complex than the
existing 'when' statement processing that has exactly the same issues if
a "when" statement becomes invalid during a config change and requires
the associated configuration to be deleted (which again can recursively
require configuration to be removed).
Alternative solutions are:
- mandate that nobody physically removes a linecard if there is still
configuration referencing it, but it is hard to enforce this in software :-)
- freeze the config from any further changes if a linecard is removed
that makes the config invalid, but this doesn't seem like a robust
solution ...
I think that the existing solution is the best approach.
A couple of further comments inline below as well ...
On 20/12/2017 21:44, Vladimir Vassilev wrote:
Hello,
On 12/20/2017 05:40 PM, Benoit Claise wrote:
Dear all,
In order not to be the bottleneck in the process and assuming that
the document will be in "publication requested" pretty soon, here is
my AD review of draft-ietf-netmod-revised-datastores-08
-
5.3.2. Missing Resources
Configuration in <intended> can refer to resources that are not
available or otherwise not physically present. In these situations,
these parts of <intended> are not applied. The data appears in
<intended> but does not appear in <operational>.
I have some concerns with this section.
Systems implementing this are expected to remove config true; nodes
while figuring the necessary changes to ensure the remaining set of
config true; nodes in operational validates against the operational
datastore model. The implementation of this is not a trivial task at
all. In order to remove configuration nodes considered inactive on the
fly one needs to remove all references to those nodes in mandatory
leafrefs in the best case and a potentially long and complex
dependency chain of YANG constrain-statements (Xpath etc.) have to be
resolved in a worse case. It is difficult to automate this. It
requires significant effort to track and remove/fix all those
dependencies just to come up with valid configuration that represents
the configuration without the "inactive" nodes which in many usecases
is completely unjustified implementation effort.
In addition in many cases it is not desirable to remove config true;
nodes that depended on a removed resource. For example:
1. A configuration instance of a filter with mandatory interface-ref
ingress and egress ports has to be removed from the operational
datastore if the egress port is removed as a physical resource. This
in effect removes the config false; statistics that might be still of
interest counting the matched traffic while the filter does not have
physical egress port to send the packets.
This isn't necessarily true. The architecture does not require that the
filter object is removed because operational is allowed to violate the
constraints. Ultimately I think that the behaviour here will depend on
implementation.
2. Alarm that is configured with mandatory reference to the missing
resource containing a counter of the elapsed time since the resource
went missing etc.
Again, the draft does not require that the alarm becomes not applied.
This also depends on the implementation.
Thanks,
Rob
I do not find any text in the draft addressing the concerns above. I
do not propose a change yet but I hope to hear what others think about
that.
Vladimir
I understand what you want to say.
Let me take an example. I have a router with a Line Card configured
and working well. if I remove the LC, the configuration should still
be in the <running> and <intended> but not in <operational>.
However, based on figure below, the notion of "inactive" nodes might
be misleading. Indeed, people might read that the LC is inactive, so
the LC configuration should not be in <intended>
+-------------+ +-----------+
| <candidate> | | <startup> |
| (ct, rw) |<---+ +--->| (ct, rw) |
+-------------+ | | +-----------+
| | | |
| +-----------+ |
+-------->| <running> |<--------+
| (ct, rw) |
+-----------+
|
| // configuration transformations,
| // e.g., removal of "inactive"
| // nodes, expansion of templates
v
+------------+
| <intended> | // subject to validation
| (ct, ro) |
+------------+
I understand that "inactive nodes" has a different meaning.
Proposal:
OLD: removal of "inactive" nodes
NEW: removal of the nodes marked as "inactive"
- In the C.1 example,
<system
xmlns="urn:example:system"
xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin">
<hostname or:origin="or:dynamic">bar</hostname>
<interface or:origin="or:intended">
<name>eth0</name>
<auto-negotiation>
<enabled or:origin="or:default">true</enabled>
<speed>1000</speed>
</auto-negotiation>
<speed>100</speed>
<address>
<ip>2001:db8::10</ip>
<prefix-length>64</prefix-length>
</address>
<address or:origin="or:dynamic">
<ip>2001:db8::1:100</ip>
<prefix-length>64</prefix-length>
</address>
</interface>
I guess it "or:dynamic" should be replaced by "or:learned"
Justification:
identity learned {
base origin;
description
"Denotes configuration learned from protocol interactions with
other devices, instead of via either the intended
configuration datastore or any dynamic configuration
datastore.
Examples of protocols that provide learned configuration
include link-layer negotiations, routing protocols,_and
DHCP._";
_Editorial:_
- number the figures
- section 8.2
This document registers two YANG modules in the YANG Module Names
registry [RFC6020 <https://tools.ietf.org/html/rfc6020>].
Following the format in [RFC6020
<https://tools.ietf.org/html/rfc6020>], the the
following registrations are requested:
duplicated "the the"
Regards, Benoit (OPS AD)
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