Hi Rob,
Thanks for the feedback. And no need to apologize since it took us much longer
to respond to your initial comments...
Please see inline.
On Tuesday, April 18, 2023, 11:55:03 AM EDT, Rob Wilton (rwilton)
<[email protected]> wrote:
Hi Reshad,
Apologies for the delay.
The changes that you have made are sufficient to clear my discuss.
As a non-discuss (and non-blocking) comment, I do still find this hierarchical
configuration to be somewhat complex on two points:
- The configuration is under optional feature statements both at the global
level and the per-interface level, and I think that the model would allow
neither feature to be specified, in which case the defaults would be ambiguous.
I’m sure that the WG has a good reason for why it is designed the way it is,
but I can’t help wondering whether it would make the model cleaner/simpler to
require support for the global level configuration, and only have per-interface
level configuration under an optional feature. I.e., if this was done, then
logically, there are always well-defined default values without requiring
evaluation of the must-statement.
<RR> Initially when I did the 2 features I was looking for a way to enforce
that at least 1 of the 2 features is supported but afaik there's no way in YANG
1.1 to do that. When I addressed your comments about config
hierarchy/inheritance, I added the must statements to address that. I did
consider removing one of the features but it wasn't clear to me which one
should be removed, in that some implementations might prefer having just global
config and others would prefer per-interface configuration. But I'm ok with
making the global config mandatory (i.e. remove the feature) if there's
consensus on that, need to discuss with the co-authors too.
- I don’t think that the descriptions are necessarily clear about if, and
how, single-interval on the interface is allowed to override
desired-min-tx-interval and required-min-rx-interval configured globally, or
vice-versa. Please consider whether it would be helpful to update the
descriptions of these fields under the interface configuration to clarify these
semantics.
<RR> Ack, I will update the description.
Regards,Reshad.
Regards,
Rob
From: Reshad Rahman <[email protected]>
Sent: 21 March 2023 01:32
To: The IESG <[email protected]>; Rob Wilton (rwilton) <[email protected]>
Cc: [email protected]; [email protected]; [email protected];
Jeffrey Haas <[email protected]>
Subject: Re: Robert Wilton's Discuss on draft-ietf-bfd-unsolicited-11: (with
DISCUSS and COMMENT)
Hi Rob,
I believe rev-12 addresses the 3 DISCUSS points below.
We still have to do further updates to the document.
Regards,
Reshad.
On Monday, December 12, 2022, 12:03:19 PM EST, Robert Wilton via Datatracker
<[email protected]> wrote:
Robert Wilton has entered the following ballot position for
draft-ietf-bfd-unsolicited-11: Discuss
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----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------
Hi,
Thanks for this document.
Please see my comments below for more details, but I'm balloting discuss on 3
points: (1) The document is somewhat unclear as to whether the configuration is
applied hierarchically (I presume that it is, if not then my second discuss
point is not valid and can be ignored). (2) As specified, I don't think that
the hierarchical configuration will work, because the interface level leaf
"defaults" will override an explicit value configured globally. I.e.,
logically, the interface level leaf, if in scope, will always have a value. (3)
The document should provide an instance-data example in the appendix to
illustrate the use of this configuration.
Regards,
Rob
----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------
Moderate level comments:
(1) p 3, sec 2. Procedures for Unsolicited BFD
When the passive side receives a BFD Control packet from the active
side with 0 as "Your Discriminator" and does not find an existing BFD
session, the passive side MAY create a matching BFD session toward
the active side, if permitted by local configuration and policy.
I'm surprised that this is only a MAY and not a SHOULD or MUST. I.e., if the
local configuration & policy allows passive BFD sessions why would they not be
created?
(2) p 4, sec 4.1. Unsolicited BFD Hierarchy
* Globally, i.e. for all interfaces. This requires support for the
"unsolicited-params-global" feature.
* For specific interfaces. This requires support for the
"unsolicited-params-per-interface" feature.
>From this description, it is unclear to me whether the features enabling global
or per-interface configuration are meant to be an either/or (in which case, the
constraint could probably be expressed in the features), or whether a server is
allowed to support configuration both globally and override the global
configuration with interface specific configuration. My subsequent discuss
comments assume the latter. Either way, it would be helpful for this text in
this section (and probably the YANG module) to be a bit more explicit on this
regard.
(3) p 8, sec 4.2. Unsolicited BFD Module
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
+ "bfd-ip-sh:interfaces" {
if-feature bfd-unsol:unsolicited-params-per-interface;
description
"Augmentation for BFD unsolicited on IP single-hop interface";
container unsolicited {
description
"BFD IP single-hop interface unsolicited top level
container";
leaf enabled {
type boolean;
default false;
I'm not sure that you want a default value specified in the YANG here since
this would have precedence over any explicitly configured global default value.
(4) p 8, sec 4.2. Unsolicited BFD Module
description
"BFD unsolicited enabled on this interface.";
}
uses bfd-types:base-cfg-parms;
You have the same issue here as above, in that the default values directly
associated with the leaves in this grouping will always take precedence over
any configured global value. I.e., the configuration, if properly implemented
cannot be hierarchical. The pragmatic solution is to copy the used grouping
inline here and delete the default statements. This has the advantage that the
descriptions can also make the hierarchical behavior of the configuration
explicit.
(5) p 9, sec 4.2. Unsolicited BFD Module
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
+ "bfd-ip-sh:sessions/bfd-ip-sh:session" {
description
"Augmentation for BFD unsolicited on IP single-hop session";
leaf role {
type bfd-unsol:role;
config false;
description
"Role of local system during BFD session initialization.";
}
}
}
<CODE ENDS>
Please add an instance data example to an appendix to illustrate the use of
this YANG model. This helps readers and can further emphasize the hierarchical
nature of the configuration.
Minor level comments:
(6) p 3, sec 2. Procedures for Unsolicited BFD
Passive unsolicited BFD support MUST be disabled by default, and MUST
require explicit configuration to be enabled. On the passive side,
the desired BFD parameters SHOULD be configurable. The passive side
MAY also choose to use the parameters that the active side uses in
its BFD Control packets. The "My Discriminator", however, MUST be
chosen to allow multiple unsolicited BFD sessions.
Rather then configured values on the passive side, did the authors consider
setting minimum configuration limits? E.g., rather than define desired
send/receive limits, instead, configure lower bounds on what the minimum tx
interval may be (to prevent DDOS attacks).
Nit level comments:
(7) p 3, sec 2. Procedures for Unsolicited BFD
The passive side MUST then start sending BFD Control packets and
perform the necessary procedure for bringing up, maintaining and
tearing down the BFD session. If the BFD session fails to get
established within certain specified time, or if an established BFD
session goes down, the passive side SHOULD stop sending BFD Control
packets and MAY delete the BFD session created until BFD Control
packets are initiated by the active side again.
Nit, within certain specified => within a specified
(8) p 6, sec 4.2. Unsolicited BFD Module
Copyright (c) 2021 IETF Trust and the persons
identified as authors of the code. All rights reserved.
This copyright statement will need to be fixed.
