Re-,

Your proposal to use "metric that excludes prefix from the route calculation" 
works for me. Thanks.

The only pending point is the UP-flag:

==

##PP3
we are not making any assumptions at all. We offer distinction if it becomes 
useful for any app.

[Med] This looks more like a bet here, Peter: assume that a single flag that 
says this a PM loss is sufficient for what these applications needs to do 
compared to reacting to the U-flag.

##PP4
yes, that was exactly what was requested by several folks in the WG. You may 
see it as a bet, but I see no harm.
==

What would be helpful is to hear from the WG about what can be achieved with 
the UP-flag, but is impossible with the U-flag alone. In other words, what are 
we losing if we drop the UP-flag?

Cheers,
Med

De : Peter Psenak <[email protected]>
Envoyé : mercredi 24 septembre 2025 11:10
À : BOUCADAIR Mohamed INNOV/NET <[email protected]>; Peter Psenak 
<[email protected]>; The IESG <[email protected]>
Cc : [email protected]; [email protected]; 
[email protected]; [email protected]
Objet : Re: [Lsr] Re: Mohamed Boucadair's Discuss on 
draft-ietf-lsr-igp-ureach-prefix-announce-09: (with DISCUSS and COMMENT)


Hi Med,

please see inline (##PP4):

On 24/09/2025 07:20, 
[email protected]<mailto:[email protected]> wrote:
Hi Peter,

I think that we are almost converging.

Please see inline.

Cheers,
Med

De : Peter Psenak 
<[email protected]><mailto:[email protected]>
Envoyé : mardi 23 septembre 2025 15:23
À : BOUCADAIR Mohamed INNOV/NET 
<[email protected]><mailto:[email protected]>; Peter 
Psenak 
<[email protected]><mailto:[email protected]>;
 The IESG <[email protected]><mailto:[email protected]>
Cc : 
[email protected]<mailto:[email protected]>;
 [email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>
Objet : Re: [Lsr] Re: Mohamed Boucadair's Discuss on 
draft-ietf-lsr-igp-ureach-prefix-announce-09: (with DISCUSS and COMMENT)


Hi Med,

please see inline (##PP3):

On 23/09/2025 14:33, 
[email protected]<mailto:[email protected]> wrote:
Re-,

Please see inline.

Cheers,
Med

De : Peter Psenak 
<[email protected]><mailto:[email protected]>
Envoyé : mardi 23 septembre 2025 13:59
À : BOUCADAIR Mohamed INNOV/NET 
<[email protected]><mailto:[email protected]>; The IESG 
<[email protected]><mailto:[email protected]>
Cc : 
[email protected]<mailto:[email protected]>;
 [email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>
Objet : Re: Mohamed Boucadair's Discuss on 
draft-ietf-lsr-igp-ureach-prefix-announce-09: (with DISCUSS and COMMENT)

Hi Med,

please see inline (##PP2):

On 23/09/2025 11:07, 
[email protected]<mailto:[email protected]> wrote:
Hi Peter,

Thanks for the follow-up.

Please see inline.

Cheers,
Med

De : Peter Psenak <[email protected]><mailto:[email protected]>
Envoyé : lundi 22 septembre 2025 17:11
À : BOUCADAIR Mohamed INNOV/NET 
<[email protected]><mailto:[email protected]>; The IESG 
<[email protected]><mailto:[email protected]>
Cc : 
[email protected]<mailto:[email protected]>;
 [email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>
Objet : Re: Mohamed Boucadair's Discuss on 
draft-ietf-lsr-igp-ureach-prefix-announce-09: (with DISCUSS and COMMENT)


Hi Med,

thanks for the comments, please see inline (##PP):

On 21/09/2025 12:21, Mohamed Boucadair via Datatracker wrote:

Mohamed Boucadair has entered the following ballot position for

draft-ietf-lsr-igp-ureach-prefix-announce-09: Discuss



When responding, please keep the subject line intact and reply to all

email addresses included in the To and CC lines. (Feel free to cut this

introductory paragraph, however.)





Please refer to 
https://www.ietf.org/about/groups/iesg/statements/handling-ballot-positions/

for more information about how to handle DISCUSS and COMMENT positions.





The document, along with other ballot positions, can be found here:

https://datatracker.ietf.org/doc/draft-ietf-lsr-igp-ureach-prefix-announce/







----------------------------------------------------------------------

DISCUSS:

----------------------------------------------------------------------



Hi Peter, Clarence, Daniel, Shraddha, and Gyan,



Thank you for the effort put into this specification.



I like the approach adopted here as it leverages exiting features (which is

good for backward compatibility) and thus eases incremental deployment.



# Meta comment



The flow of the document can be made better by introducing the explicit

signaling part early in the document as that is what actually demux the use

defined in the draft vs. any other future uses of the specific metric. The

current flow reveals that the signaling part was added as an after though, not

as part of the design.

##PP2
the document has been re-ordered several times based on the comments during 
various stages of the review process.
I'm a bit reluctant to change it again, as different people have a different  
priorities, and it's not possible to make everyone happy.
In the end, what we are specifying is rather simple, so the ordering does not 
play that significant role IMHO.

[Med] I understand, but I still think this is important to fix. FWIW, as part 
of this review, I have checked implementations available out there and I was 
puzzled by one UPA implementation that says "UPA flags are not supported".

The current structure reveals this issue: the support/advertisement/propagation 
are specified separately than signaling (which is the core of the extension and 
which justifies at the first place the PS status). The signaling part should be 
integrated in the "Supporting ..." part.

##PP2
done

[Med] Thanks.



   3.  Supporting UPA in IS-IS . . . . . . . . . . . . . . . . . . .   5

     3.1.  Advertisement of UPA in IS-IS . . . . . . . . . . . . . .   5

     3.2.  Propagation of UPA in IS-IS . . . . . . . . . . . . . . .   6

   4.  Supporting UPA in OSPF  . . . . . . . . . . . . . . . . . . .   6

     4.1.  Advertisement of UPA in OSPF  . . . . . . . . . . . . . .   7

     4.2.  Propagation of UPA in OSPF  . . . . . . . . . . . . . . .   8

   5.  Signaling UPA . . . . . . . . . . . . . . . . . . . . . . . .   8

     5.1.  Signaling UPA in IS-IS  . . . . . . . . . . . . . . . . .   8

     5.2.  Signaling UPA in OSPF . . . . . . . . . . . . . . . . . .   9

       5.2.1.  Signaling UPA in OSPFv2 . . . . . . . . . . . . . . .   9

       5.2.2.  Signaling UPA in OSPFv3 . . . . . . . . . . . . . . .   9





Please find below some DICUSS points:



# Planned Maintenance



I expect that adequate reconfiguration will be put in place to isolate a node

for PM purposes. The document does not explain how the signal defined here is

needed or solves an issue. I appreciate that the introduction include a short

mention of the use of overload bit, though.



I'm also asking the question because there is no ** normative ** discussion (at

least I missed it) about how that can be triggered at the originating ABR.



Also, unlike a random failure, a planned failure is associated with an expected

start and end times. Signaling the event without those characteristic questions

the value of tagging a loss as an NP.

##PP
I'm not sure what is being asked. This document does not specify the PM 
procedure of any kind.
This document specifies the UPA signaling, including the bit that signals that 
the UPA was originated on the ABR/ASBR as a result of the PM in its source 
area/domain.

UPA helps in propagating the information about the connectivity loss caused by 
the beginning of the PM outside of the area/domain. That's all.

[Med] The main point is what issue are we solving by indicating a planned 
failure, compared to sole use of U-flag? What we lose if the UP-flag is removed?

##PP2
application that uses these flags may treat them differently. That's all. We 
are not specifying the application treatment of any of these flags, but we 
offer the distinction.

[Med] We are making hidden assumptions here as we don't know why these 
applications need such signal, how they intend to make use of the UP-signal, 
whether a simple additional flag is sufficient from them compared to what is 
already exposed with U-flag, etc.

##PP3
we are not making any assumptions at all. We offer distinction if it becomes 
useful for any app.

[Med] This looks more like a bet here, Peter: assume that a single flag that 
says this a PM loss is sufficient for what these applications needs to do 
compared to reacting to the U-flag.

##PP4
yes, that was exactly what was requested by several folks in the WG. You may 
see it as a bet, but I see no harm.







Also, we don't say how the UP-flag is triggered.

##PP3:

Section 2 says:

UPA MAY be generated by an ABR or ASBR for a prefix that is

   summarized by the summary prefix originated by an ABR or ASBR in the

   following cases:



   1.  Reachability of a prefix that was reachable earlier was lost.



   2.  For any of the planned maintenance cases:



          - if the node originating the prefix is signalling the

          overload state in IS-IS, or or H-bit in OSPFv2 [RFC8870], or

          R-bit in OSPFv3 [RFC5340] .



          - the metric to reach the prefix from an ABR or ASBR crosses

          the configured threshold.



(2) is specific for planned maintenance. That's when the UP flag is set.





# Configuration Efficiency



Section 2

   Implementations MAY limit the UPA generation to specific prefixes,

   e.g.  host prefixes, SRv6 locators, or similar.  Such filtering is

   optional and MAY be controlled via configuration.



I'm afraid that for the limit to be useful, it should be tweaked based on local

operator policy and not on some magic that is internal to the implementation. I

suggest the second MAY to be changed to SHOULD when such limit is supported.
##PP
done
[Med] Thanks.





Idem for the following:

   Implementation MAY provide a configuration option to specify the UPA

   lifetime at the originating ABR or ASBR.



I suggest we update it to:



   UPA implementations SHOULD provide a configuration option to specify the UPA

   ^^^^^^^^^^^^^^^^^^^

   lifetime at the originating ABR or ASBR.
##PP
done
[Med] Thanks.





The reasoning for this change is that a failure may last long and that an

operator would like to maintain that loss state longer (than allowed by a

default limit) to accommodate how the specific application consuming the loss

signal.



Please note that you say that the validity depends on the use case:



CURRENT (S.2):

   The

   time the UPA is kept in the network SHOULD also reflect the intended

   use-case for which the UPA was advertised.



# Withdrawal



Section 2 says:



   UPA advertisements SHOULD

   therefore be withdrawn after some amount of time, that would provides

   sufficient time for UPA to be flooded network-wide and acted upon by

   receiving nodes, but limits the presence of UPA in the network.  The

   time the UPA is kept in the network SHOULD also reflect the intended

   use-case for which the UPA was advertised.

   ...

   ABR or ASBR MUST withdraw the previously advertised UPA when the

   reason for which the UPA was generated ceases - e.g. prefix

   reachability was restored or its metric has changed such that it is

   below the configured threshold value.



The second MUST is not useful if that reason disappears before the timeout that

triggers the SHOULD.



I think a simple text reorder would fix this. For example,



NEW:

   ABR or ASBR MUST withdraw the previously advertised UPA when the

   reason for which the UPA was generated ceases - e.g. prefix

   reachability was restored or its metric has changed such that it is

   below the configured threshold value.



   Even if the reasons persist, UPA advertisements SHOULD

   be withdrawn after some amount of time, that would provides

   sufficient time for UPA to be flooded network-wide and acted upon by

   receiving nodes, but limits the presence of UPA in the network.  The

   time the UPA is kept in the network SHOULD also reflect the intended

   use-case for which the UPA was advertised.

##PP
done

[Med] ACK



# Scalability control



Section 2 says:

   It is also RECOMMENDED that implementations limit the number of UPA

   advertisements which can be originated at a given time.



The benefits gained by summarization may be nullified if a large number of UPAs

are injected. This recommendation is really great, but there is a need to

expose a configuration parameter here. Pease



NEW:

   UPA implementations SHOULD provide a configuration option to limit

   the number of such UPAs.

##PP
done.

[Med] ACK



# Backward compatibility Check



CURRENT (3.2/4.2):

   Such requirement of

   reachability MUST NOT be applied for UPAs, as they are propagating

   unreachability.



Does this mean that an ABR that don't support UPA might discard it?

##PP
it will not discard it, bit it will not propagate it between areas.

[Med] OK. This confirms what I had in mind: for the feature to be useful, all 
ABRs should upgraded. Can you please indicate this in the operational 
considerations section? Thanks.

##PP2

Section 4.2 says (updated based on Ketan's comment):

     "OSPF ABRs, which would be responsible for propagating
       UPA advertisements into other areas need to recognize such 
advertisements.
       Failure to do so would prevent UPA to reach the routers in the remote 
areas."

[Med] This is a great addition. I still prefer we group these considerations 
under an OPS consideration section as this is more about how to operate the 
protocol extension.
##PP3
I believe what we have is sufficient. As far as I know operational section is 
not mandatory, at least not yet. I wish it never becomes.




I added similar text to section 3.2 for consistency and completeness:

       "ISIS L1/L2 routers, which would be responsible for propagating UPA
        advertisements between levels need to recognize such advertisements.
        Failure to do so would prevent UPA to reach the routers in the remote 
areas.

That should be sufficient I believe.

[Med] Thank you.





# Avoid redefining exiting behaviors



CURRENT (Section 4):

   In addition, NU-bit is defined for OSPFv3 [RFC5340].  Prefixes having

   the NU-bit set in their PrefixOptions field SHOULD NOT be included in

   the routing calculation.



The SHOULD NOT part is already defined in 5340. What is this redefined again?

##PP

I changed to:

"Prefixes having  the NU-bit set in their PrefixOptions field are not included 
in the routing
 calculation."

Is that ok? Without any text it's not clear what's the relevance of the NU bit 
here.

[Med] It is better. You can add a pointer to Section 4.8.1 of [RFC5340].

##PP2:
pointer to RFC5340 is provided in the previous sentence:

"In addition, NU-bit is defined for OSPFv3 [RFC5340]. Prefixes having the 
NU-bit set in their PrefixOptions field are not included in the routing 
calculation."

[Med] Having an explicit pointer where to look in that RFC will be convenient 
for readers.





# Check on "UP-Flag" is useless



5.1.1

   The prefix that is advertised with U-Flag or UP-Flag  MUST have the

   metric set to a value larger than 0xFE000000.  If the prefix metric

   is less than or equal 0xFE000000, both of these flags MUST be

   ignored.



5.2.2

   The prefix that is advertised with U-Flag or UP-Flag MUST have the

   NU-bit set in the PrefixOptions of the parent TLV.



The "or UP-Flag" part of both MUSTs is useless as U-Flag will be set in such

case as well. The case where only UP-Flag is set is invalid and will be ignored.



Unless I missed a subtle thing here, please update these two.

##PP
good catch, fixed it.
We changed the UP flag from standalone one to be suplementary, but we forgot to 
update the text.

[Med] Thanks.





# Service stability



The document declares the applications that consume the signal out of scope.

Which is fine. However, there might be some negative implications due to how

the loss signal (or it withdrawal/absence) is interpreted. For example, add a

warning to insist that withdrawal does not mean revert to a nominal state.

Having few sentences for these service to take appropriate measure before

reverting.

##PP

The usage of the UPA depends on the application. As we may not know what 
applications are going to use it, I would be reluctant to specify the 
application behavior.

[Med] This is not about specifying the behavior but indicating precaution that 
these applications need to take care of.

For some applications, the presence of the UPA may be required, before the 
application itself detects the loss later.

Section 2 says:
"ABR or ASBR MUST withdraw the previously advertised UPA when the reason for 
which the UPA was generated ceases"

In such case the withdrawal could mean that the prefix for which the UPA was 
generated became reachable again.

[Med] but we also withdraw UPA after a timer even if the reachability is not 
OK. Depending solely on the absence of UPA to infer that reachability is back, 
is not deterministic.

UPA is a one time signal for applications that there might be some loss of 
connectivity. Application itself must use its own mechanism to verify/detect 
the loss eventually. In the meantime it may decide to do some proactive 
measures, but UPA does not dictates the application behavior.

[Med] We just need to say so in the OPS consideration section.

##PP2

I added the following text at the end of the "Processing of the UPA" section:

     "Applications using the UPA cannot use the absence of the UPA to infer 
that the
       reachability of the prefix is back. They must rely on their own 
mechanisms to verify
       the reachability of the remote end-points."

[Med] Looks good to me. Thanks.



----------------------------------------------------------------------

COMMENT:

----------------------------------------------------------------------



# Topology-dependent matters



Abstract:

   This enables fast

   convergence by steering traffic away from the node which owns the

   prefix and is no longer reachable.



"steering.." part of the text is only possible when there alternate routes for

that prefix. Otherwise, the traffic will be dropped anyway.



Pleas reword. For example, saying "when applicable" or similar would be just

fine.

##PP
done

[Med] Thanks.





# Why now?



Summarization was there since decades. A mention about what exacerbates the

need for this new feature now (and was not considered as a major issue in past)

would be helpful.

##PP
is it really required? I was not planning to mention it in the text . But if 
you insist...

[Med] As a reader, it is helpful to understand this.

It's the SRv6 that brings summarization back in life for underlay (IGPs). With 
MPLS summarization was not possible.

[Med] I see that Robert/Joel have some comments on this. I trust that some 
motivation that captures the discussion will be recorded in the draft. Thank 
you.
##PP2
I intentionally did not want to spark that discussion and that was the reason 
there was no such text there. I would rather leave it that way.
[Med] Up to you to decide here.



# "Egress" depends on the traffic directionality



Section 1:

   Similarly, when an egress router needs to be taken out of service for

   maintenance, the traffic is drained from the node before taking it

   down.



A router may behave as ingress/egress as a function of traffic direction. I

would delete "egress" here.
##PP
done
[Med] ACK






# (ni) There might be many ABRs per area, not single one



Please make this change in Section 1 (and similar):



OLD:

   When prefixes from such node are summarized by the

   Area Border Router (ABR) or Autonomous System Boundary Router (ASBR),



NEW:

   When prefixes from such node are summarized by an

   Area Border Router (ABR) or Autonomous System Boundary Router (ASBR),

##PP
done

[Med] ACK





# (Operational Considerations) Many signals, distinct expected uses



Section 1 has the following:



   This document does not define how to advertise prefix that is not

   reachable for routing.  That has been defined for IS-IS in [RFC5305]

   and [RFC5308], for OSPF in [RFC2328], and for OSPFv3 in [RFC5340].



I wonder whether we can list the signals available out there (explicit prefer

advertisement, prefix with a specific metric, etc.) and remind the intend use

scope for each of them. This can be record in the Operational Considerations.

##PP
that is what the beginning of section 3 and 4 are doing for ISIS and OSPFv2/v3 
respectively.

[Med] Yeah, but that is lost in the mass. Moving/extending that part is as a 
helpful operational considerations to clarify the scope for each of these tools 
and this help those who will deploy.
##PP2
I don't feel it's lost.
[Med] That's fine as an author. But, I'm approaching this from distinct 
perspective: as an operator who want to digest how this is different from the 
tools already.

##PP3
as an operator, you are only interested in one protocol. As such you are only 
going to read the section that is specific to that protocol. That is my 
experience with operators :)



The document is organized in a protocol specific sections because historically 
different mechanisms were defined for each protocol. Section 3.1 and 4.1. 
discuss in detail the existing protocol mechanisms. I don't see a need for the 
operational section that repeats the same thing.
[Med] It does not to repeat things, but better structure some of the content 
you already have.





I'm raising this point, especially that the text right after says the following

without appropriate scoping:



CURRENT:

   This document defines two new flags in IS-IS, OSPF, and OSPFv3.

   These flags, together with the existing protocol mechanisms, provide

   the support for advertising prefix unreachability , together with the

   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

   reason for which the unreachability is advertised

##PP
what do you mean by "without appropriate scoping"?

[Med] Saying that « the support for advertising prefix unreachability" may be 
interpreted that we are advertising explicit prefix reachability, while we are 
not.

##PP2
I still do not follow. Protocols have been defined to advertise explicit prefix 
reachability day one. Nothing changes there. We are defining a way to advertise 
explicit prefix unreachability.

[Med] We are defining a reachability loss not signaling whether a prefix is 
UP/DOWN. These are distinct things in my mind.
##PP3

we are defining unreachability signaling which is needed for something that has 
not been signaled as reachable previously - for the summarization use case, the 
reachability of the summary component was never signaled.

For what has been signalled as reachable previously, the withdrawal of such 
advertisement makes it unreachable.

Anyway, back to your comment, what exactly do you suggest we do?

[Med] At least, s/ advertising prefix unreachability/advertising prefix 
unreachability loss

##PP4

I hope you meant "prefix reachability loss" not "prefix unreachability loss"

I'm sorry, but that would be incorrect. Advertising prefix reachability loss is 
something that exists in LS protocols today. If the prefix x/y was advertised 
from the originagtor Z, Z will signal the
prefix reachability loss by withdrawal of the x/y adverisement.

What we specify here is different. We are specifying a mechanism how Z can make 
unreachable x/y that he never advertised. And that is what we call 
unreachability signaling.

The fact that x/y reachability is covered by the advertisement of some other 
less specific prefix is not significant from the signaling perspective that we 
are specifying here.



# Unreachable metric?!



Section 1 has the following:

   This document defines a method to signal a specific reason for which

   the prefix with unreachable metric was advertised.



Unless, I'm mistaken there is no such "unreachable metric" as a thing in IS-IS.

##PP
Please see the section 3 of this document that mentions 
[RFC5305<https://www.rfc-editor.org/info/rfc5305>]. That RFC defines a metric 
that makes the prefix "not reachable" for the purpose of the routing.

[Med] I'm not sure to follow here. I interpret that metric as exclude it from 
SPF calculation, not more than that.
##PP2
if you exclude it from the SPF calculation, you are making it unreachable, 
don't you?
[Med] No, because reachability of that prefix depends whether that prefix is 
included, e.g., another aggregate advertised with a "normal" metric.

##PP3

 I'm afraid we are diverting from your original comment. The term "unreachable 
metric":

RFC2328 calls the LSInfinity metric as unreachable:

LSInfinity

        The metric value indicating that the destination described by an

        LSA is unreachable.

RFC5305<https://www.rfc-editor.org/info/rfc5305> does the same, just calls it 
differently.

If you have a better term how to refer to "unreachable metric" please suggest. 
We have been using this term for many years in LSR WG and everybody understand 
its meaning.

[Med] s/ the prefix with unreachable metric/the prefix with a specific metric 
(Section XX) (then point to the section where the extact metric are listed).

##PP4
this document does not define unrechable metric, that has been defined by 
existing RFCs for both OSPF and ISIS. OSPF calls such metric "unreachable 
metric", ISIS calls it "metric that MUST NOT be considered during the normal 
SPF computation".

Calling this a "specific metric" is simply incorrect.

I can use "metric that excludes prefix from the route calculation" or something 
of that nature if you really insist, even though I strongly believe that 
"unreachable" is far better.

thanks,
Peter



The term "unreachable metric" is a common term used in LS protocol community 
for such metric for last three decades.

We are reusing such metric value for UPA.





# (Operational Considerations) Activation default



Section 2 has the following:

   UPA MAY be generated by the ABR or ASBR for a prefix that is

   summarized by the summary address originated by the ABR or ASBR in

   the following cases:



Can we say something about whether the use of UPA be enabled or disabled by

default?

##PP
I added the following text as a response to one of the Ketan's comments:

"Generation of the UPA at the ABR or ASBR is optional and SHOULD be controlled 
by
 a configuration knob."

I would leave the default behavior for the implementations to decide. I see no 
reason why an RFC should mandate any specific default behavior.

[Med] For this specific case, UPA will be useful of enabled in all ABRs. I 
would this expect this to be disabled by default.
##PP2

why?

[Med] Because coordination is needed at level of a network to make use of a 
feature. Use of distinct defaults may lead to extra work and sub optimal 
behavior (e.g., some operators may introduce some nodes/functions with default 
picked by a vendor).

##PP3
not that I necessarily agree, but I added "It SHOULD be disabled by default." 
in section 2:



   Generation as well as propagation of the UPA at an ABR or ASBR is

   optional and SHOULD be controlled by a configuration knob. It SHOULD be 
disabled by default

[Med]  Looks good to me. Thanks.

thanks,
Peter



I'm going to repeat myself, but the role of the IETF is to maintain 
interoperability, not to tell implementations what defaults to use. It's the 
implementation choice and it's the reposnsibility of the field to push vendors 
to what the defaults should be if needed. There is no role for IETF to play 
there IMHO.





# Threshold



Section 2 says:

          - the metric to reach the prefix from the ABR or ASBR crosses

          the configured threshold.



Can we explicit the threshold we are referring to here + add reference where to

look at?

##PP
there is no explicit threshold here, it's any value of the metric that the 
operator defines. For example, if for the planned maintenance the cost of 
router's links is set to some high value X, the operator may set the threshold 
on the ABR to X + something.

[Med] Thanks. May be s/the configured threshold/a configured threshold
##PP2
done
[Med] ACK.










# Explicit references in Section 3



OLD:

   [RFC5305] defines the encoding for advertising IPv4 prefixes using 4

   octets of metric information.  Section 4 specifies:

   ..

   Similarly, [RFC5308] defines the encoding for advertising IPv6

   prefixes using 4 octets of metric information. Section 2 states:



NEW:

   [RFC5305] defines the encoding for advertising IPv4 prefixes using 4

   octets of metric information.  Section 4 of [RFC5305]  specifies:

   ..

   Similarly, [RFC5308] defines the encoding for advertising IPv6

   prefixes using 4 octets of metric information.  Section 2 of [RFC5308]

   states:

##PP
Ketan made a similar comment and the text has been updated already.

[Med] ACK.





# "Advertisement of UPA in IS-IS"



CURENT (S3.1)

   Recognition of the advertisement as UPA is only required on routers

   which have a valid use case for this information.



I would delete this sentence as this section is about the originator.

##PP
done

[Med] Thanks.





# Section 6



Consider moving that section right after current Section 7 as a subsection of

an Operational Consideration section.

##PP
done

[Med] ACK







## Multiple ABRs



That section may also discuss whether there are specific consideration to take

into account, e.g., presence of multiple ABRs with announces UPAs for a set of

prefixes in an area and measures to prevent routing stability. If you don't see

any risk out there, saying that as well would be useful.
##PP
there is no special risk with multiple ABRs - if the egress PE goes down they 
will all equally see it and generate the UPA. The problem is when one ABR sees 
the egress PE reachable and other as unreachable. This can only happen when the 
area partitions. That problem is described in section 6.

[Med] I like explanation with PEs, better. The case I had in mind is, e.g., a 
multi-ABR case with anycast prefixes injected via distinct PEs but a failure 
only occurs at one PE leg. Probably there is no issue at all.





## Consider adding any implications (or absence of) explicit withdrawal of an

UPA.

##PP
I'm not sure what do you mean by explicit withdrawal. UPA must be withdraw by 
the originator in all cases.

[Med]  I understand that by withdrawal we mean "to not advertise".
##PP2
yes

thanks,
Peter

Either based on the timeout, or because the reason for which it was generated 
does not exist anymore, whatever comes first.

thanks,
Peter







Cheers,

Med





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