Thanks for your review. I have posted revision -04 which I believe
addresses your substantive comments.
On 1/3/2018 8:01 AM, [email protected] wrote:
Hi,
As shepherd of this document, please find below some comments that I have:
Overall comments:
-Please add a section that contains all the abbreviations expansions:
that may help non expert people to follow the acronyms without looking
for the first reference in the text.
This is not generally required of an RFC.
-I usually like figures. For the intro, it may be wonderful to build a
figure that reminds the existing S-PMSI/Leaf A-D procedure. So without
reading the text, we can remember how it works.
-The interAS case may also be better with a Figure and an example (or
couples of).
This seems like a matter of taste. Admitedly, I'd probably like figures
more if I had any skill in producing them ;-)
Introduction:
“By originating one of these BGP routes, an ingress node advertises that
it is transmitting a particular multicast flow.”
[SLI] Is “is transmitting” correct ? Can’t we have situations where an
S-PMSI route is/was advertised but no traffic is flowing (no yet
started or switched, or stopped).
Fixed.
“Now
suppose that the ingress node wants explicit tracking for each
individual flow that it transmits (following the procedures of
[RFC6625] on that P-tunnel.”
[SLI] Missing “)”
Fixed.
“This allows the
ingress node to determine the set of egress nodes that are receiving
flows from the ingress node.”
[SLI] I think the Leaf A-D tells that there is a receiver interested
by the flow, but does not tell that it actually receives it.
Correct; fixed.
“ Howver, this procedure requires several clarifications:”
[SLI] There is a typo s/Howver/However/
Fixed.
“The procedures of [RFC6625] do not clearly state how to handle an
S-PMSI A-D route if its NLRI contains wild cards, but its PTA
specifies "no tunnel info".”
[SLI] I quickly ran over RFC6625, it does not mention anything on
explicit tracking or Leaf A-D routes.So we assume that RFC6513/6514
only applies here.
RFC 6625 specifies the handling of wildcard S-PMSI A-D routes, but did
not consider the case where the S-PMSI A-D routes do not carry a PTA.
This document corrects that.
“ * The explicit tracking procedures do not allow an ingress node
to "see" past the boundaries of the segmentation domain.
This particular problem is not further addressed in this
revision of this document.
“
[SLI] Do you plan to address it ? Or do we now consider it as out of
scope ?
I think this is actually addressed in Section 5.3, so I've removed the
remark.
Section 2:
“Prior specifications define one flag in the PTA, the "Leaf Info
Required" (LIR) flag, that is used for explicit tracking.”
[SLI] Please point to the right reference
Fixed.
“If the LIR-pF flag is set in a given PTA, the LIR flag of that PTA
SHOULD also be set.”
[SLI] Why not using a MUST ?
If all the PEs support the LIR-pF flag, the procedures will work as
intended even if the LIR flag is not set. So I don't think a MUST is
appropriate.
“one forces a
a response to be sent an egress node that does not support LIR-pF”
[SLI] Is there a missing word like ‘sent by an egress node” ?
Fixed.
Section 3:
“The definition of "match for reception" in [RFC6625] is hereby
modified as follows:”
[SLI] Please point to the section that you are updating.
In addition, section 3.2 of RFC6625 contains multiple if then else
conditions for each cases (C-S,C-G) and (C-*,C-G). Please give some
precision in where do you want to insert your new statement in this
processing sequence. I guess it is at the beginning.
I tried to make this clearer.
“When finding the "match for reception" for a given (C-S,C-G) or
(C-*,C-G), ignore any S-PMSI A-D route that has no PTA, or whose
PTA specifying "no tunnel information".”
[SLI] I would be in favor to introduce a normative statement here.
Fixed.
“We also introduce a new notion: the "match for tracking". This
differs from the "match for reception" as follows:”
[SLI] It would be better to give a definition of the “match for
tracking” before giving the rules. Here you’re explaining only the
rules, not the difference in the meaning. Wouldn’t it be easier to
tell that the implementation MUST consider only the S-PMSI A-D routes
that have a LIR flag and/or LR-pF flag set and then run the same rules
as the RFC6625. Why do you want to have S-PMSI routes with PTA and LIR
unset in your route list for “match for tracking” ? You need to take
care here on your text proposal as one of your previous statement
updates the RFC6625 and the match reception procedure, so the rules to
be applied are the original one from RFC6625 and not the updated one.
IMO, the clearest way to express this is to give the rules and then
illustrate with a couple of examples.
“ Also note that if a match for tracking does not have the LIR flag or
the LIR-pF flag set, no explicit tracking information will be
generated. See Section 5.”
[SLI] Again I do not see the value added of keeping such route as a
match for tracking as there is no tracking requested.
As the terms are defined, there is always a "match for tracking" route
for each flow. If tracking is not requested, this route will have LIR
and LIR-pF clear. There are no unnecessary routes.
Section 4:
“Such a route could be an
I-PMSI A-D route, a (C-*,C-G1) S-PMSI A-D route, a (C-S1,C-*)
S-PMSI A-D route, or a (C-*,C-*) S-PMSI A-D route. “
[SLI] Is per flow explicit tracking also required for I-PMSI ? I do
not see it listed in the goals of the doc ? The goal was to address
wildcards S-PMSI AD routes.
The above simply says that some route must specify the tunnel on which
the (C-S1,C-G1) is to be transmitted, and that this route could be an
I-PMSI A-D route.
“Further, if the ingress node originates a wildcard S-PMSI A-D
route carrying a PTA specifying the tunnel to be used for
carrying (C-S1,C-G1) traffic, and if that PTA has the LIR-pF bit
set, then explicit tracking for (C-S1,C-G1) is requested by that
S-PMSI A-D route. Thus the ingress node SHOULD NOT originate a
(C-S1,C-G1) S-PMSI A-D route whose PTA specifies "no tunnel
info"; such a route would not provide any additional
functionality.”
[SLI] I do not fully understand this text in the context of your
procedure 1. which deals with an origination of an (C-S1,C-G1) S-PMSI
A-D route (no wildcard). As I understand the procedure for the
wildcard is defined in 2.
This just says that there's no point in originating S-PMSI(C-S,C-G) with
LIR set if you've already originated S-PMSI(C-*,C-G) with LIR-pF set.
That seems to be an appropriate bit of advice.
“2. The following procedure can be used if (and only if) it is known
that the egress nodes support the optional LIR-pF flag.”
I have some issue with this sentence. It does not seem to be normative
as there is no normative statement. However I understand it as a
critical thing (“and only if” !) so it may require at least a SHOULD.
Then the issue I see is that this knowledge does not come from the
protocol, so it sounds important to me to highlight the impact of a
mistake.
BUT, reading the section 5. I understand that it is not as critical as
it seems as the receiver will ignore simply the LIR-pF flag and apply
the standard procedure (LIR set).
Please clarify the criticity to have or not this knowledge.
I added some text saying that procedure 2 may yield unexpected results
if not all the PEs support LIR-pF, and that the procedure SHOULD NOT be
used in that case.
“ To terminate explicit tracking that has been initiated by an
S-PMSI A-D route whose PTA specifies a tunnel, the ingress node
re-originates the route without the LIR flag set”
[SLI] Do we also need to clear the LIR-pf ? It would make sense to do so.
Fixed.
“If the match for tracking has LIR set and if either (a) the
egress node does not support LIR-pF, or (b) LIR-pF is not set,
then the egress node must respond to the match for tracking,
following procedures specified in other documents for the case
where LIR is set.”
[SLI] Please state the relevant document references here.
In the case described above, the handling of the LIR flag is not
modified by this document. I don't think it is necessary to cite a
specific set of documents that discuss the LIR flag.
Section 5.2
“Note that, per RFC4364, every RD begins with a two-octet type field
that is either 0, 1, or 2. By adding 16 to the second octet of the
RD, we force the type field to be 16, 17, or 18. “
[SLI] It works but we may need to ensure that the types > 16 cannot be
used anymore by new applications.
There is a registry for the Route Distinguisher Type field. Only types
16, 17, and 18 are defined here, other values are still available.
Moreover if new RD types are created, new siblings will have to be
created.
Your point is correct, but there hasn't been a new RD type in 20 years.
The draft shouldn't really say "add 16", it should just point out the
new types.
Wouldn’t it be easier to set the MSB of the RD type to 1 ? so we only
lock half of the type space.
I think it is easier to use three new type values than to turn one of
the bits into a flag.
Or what could be the impact of using the RD of the local VRF of the
egress node ?
The RD of the Leaf A-D route needs to be derived from the RD of the
S-PMSI A-D route that elicits it. Otherwise the ingress node receiving
the Leaf A-D route will have diffculty matching it to the corresponding
S-PMSI A-D route.
Section 5.3
“In the case where the egress
node is not a PE, but rather an ABR or ASBR, it will not know whether
it needs to receive a given flow unless it receives a Leaf A-D route
whose NLRI specifies that flow and whose IP-address-specific RT
specifies an address of the egress node.”
[SLI] The sentence works but when reading it I needed multiple reread
to understand that the “IP-address-specific RT
specifies an address of the egress node.” was referring to the
ASBR/ABR and not the receiver PE.
Do you mind using “this egress node” or “this ABR/ASBR” ?
I tried to clarify that.
Section 8.
[SLI] Do we have counter-measures against such “attack” ? Ingress PE
dropping ?
I consider the specification of such counter-measures to be outside the
scope of the document.
Section 9.2
I think RFC7524 needs to be referenced as normative giving that its
knowledge is required to understand section 5.3.
I'm not sure that RFC7524 should be a normative reference, as this draft
does not require segmentation at the ABRs. However, since RFC7524 is
already published, there's no harm in adding it to the "normative
references" section.
I think that section 5.3 is also updating/complementing the procedures
in RFC7524 with the “no-tunnel info” case.
There don't seem to be any clear and objective criteria for determining
whether one document "updates" another.
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