From: Shraddha Hegde <shraddha@juniper.net>
To: Peter Psenak <ppsenak@cisco.com>, "internet-drafts@ietf.org"
 <internet-drafts@ietf.org>, "i-d-announce@ietf.org" <i-d-announce@ietf.org>
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Thread-Topic: [OSPF] I-D Action:
 draft-ietf-ospf-segment-routing-extensions-13.txt
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Date: Thu, 11 May 2017 09:30:55 +0000
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Subject: Re: [OSPF] I-D Action:
 draft-ietf-ospf-segment-routing-extensions-13.txt
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Peter,

Inter-area/external prefixes with A-flag re-set is the only scenario
I can think of where SRMS SIDs should not do PHP.
Is there any other case?

> "For all other cases, when SID is coming from SRMS, PHM MUST not be done"
I suggest the text to be more specific to the cases since we do=20
not have many scenarios to list.=20

Rgds
Shraddha
-----Original Message-----
From: Peter Psenak [mailto:ppsenak@cisco.com]=20
Sent: Thursday, May 11, 2017 2:46 PM
To: Shraddha Hegde <shraddha@juniper.net>; internet-drafts@ietf.org; i-d-an=
nounce@ietf.org
Cc: ospf@ietf.org
Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-segment-routing-extensions-=
13.txt

Hi Shraddha

please see inline:

On 11/05/17 08:49 , Shraddha Hegde wrote:
> Peter,
>
> It is clearly specified that ABR originating prefixes from other areas=20
> should have NP Bit set.
>
> "The NP-Flag (No-PHP) MUST be set for Prefix-SIDs allocated to inter-
>     area prefixes that are originated by the ABR based on intra-area or
>     inter-area reachability between areas.  When the inter-area prefix is
>     generated based on a prefix which is directly attached to the ABR,
>     the NP-Flag SHOULD NOT be set."
>
>
> The same behavior should apply to mapping server advertised advertisement=
s as well.

when SRMS advertises the SID, it can not set the NP-Flag, so we can not app=
ly the exact same behavior there.

>
> " As the Mapping Server does not specify the originator of a prefix
>>      advertisement, it is not possible to determine PHP behavior solely
>>      based on the Mapping Server advertisement.  However, PHP behavior
>>      SHOULD be done in following cases:
>>
>>         The Prefix is intra-area type and the downstream neighbor is the
>>         originator of the prefix.
>>
>>         The Prefix is inter-area type and downstream neighbor is an ABR,
>>         which is advertising prefix reachability and is also generating
>>         the Extended Prefix TLV with the A-flag set for this prefix as
>>         described in section 2.1 of [RFC7684]."
>
>
> While the text above captures the case of directly attached prefixes=20
> it does not cover the Case of re-distributed prefixes for mapping server =
advertisements.

there is a text in the draft right after the above mention text that talks =
about the redistribution case:

       "The Prefix is external type and downstream neighbor is an ASBR,
       which is advertising prefix reachability and is also generating
       the Extended Prefix TLV with the A-flag set for this prefix as
       described in section 2.1 of [RFC7684]."


>
> Suggest to add below text.
>
>          "The Prefix is inter-area type and downstream neighbor is an ABR=
,
>          which is advertising prefix reachability and is also generating
>          the Extended Prefix TLV with the A-flag re-set for this prefix a=
s
>          described in section 2.1 of [RFC7684] then PHP MUST not be done"


the draft says when PHP should be done when the SID is coming from the SRMS=
. It assumes that in all other cases PHP is not done.

If we are going to say when the PHP must not be done for SID coming from SR=
MS, we need to list all cases, not only one of them.

So I would say we either not say anything, or we say:

"For all other cases, when SID is coming from SRMS, PHM MUST not be done"

thanks,
Peter


> Rgds
> Shraddha
>
> -----Original Message-----
> From: Peter Psenak [mailto:ppsenak@cisco.com]
> Sent: Wednesday, May 10, 2017 12:33 PM
> To: Shraddha Hegde <shraddha@juniper.net>; internet-drafts@ietf.org;=20
> i-d-announce@ietf.org
> Cc: ospf@ietf.org
> Subject: Re: [OSPF] I-D Action:=20
> draft-ietf-ospf-segment-routing-extensions-13.txt
>
> Hi Shraddha,
>
> please see inline:
>
> On 10/05/17 07:34 , Shraddha Hegde wrote:
>> Authors,
>>
>> Apologies for being late with this comment in the process of standardiza=
tion.
>>
>> The below section 5 describes the PHP for mapping server
>>
>>
>> " As the Mapping Server does not specify the originator of a prefix
>>      advertisement, it is not possible to determine PHP behavior solely
>>      based on the Mapping Server advertisement.  However, PHP behavior
>>      SHOULD be done in following cases:
>>
>>         The Prefix is intra-area type and the downstream neighbor is the
>>         originator of the prefix.
>>
>>         The Prefix is inter-area type and downstream neighbor is an ABR,
>>         which is advertising prefix reachability and is also generating
>>         the Extended Prefix TLV with the A-flag set for this prefix as
>>         described in section 2.1 of [RFC7684]."
>>
>>
>> The text says "PHP behavior" should be done in following cases.
>> In the second case here it's an ABR re-advertising a prefix and SID=20
>> being advertised for this Prefix from a mapping server. If we interpret =
"PHP behavior should be done"
>> As the penultimate router removing the label and forwarding the=20
>> packet to ABR, It does not work since the inner labels gets exposed at t=
he ABR.
>
> above texts clearly specifies that PHP is done only for case where ABR is=
 originating a prefix, not propagating it from other area. You can distingu=
ish between the two based on the A-flag in the Extended Prefix TLV as speci=
fied in RFC7684, which the above text mentions.
>
> thanks,
> Peter
>>
>> Request authors to add clarification text around "PHP behavior".
>>
>> Rgds
>> Shraddha
>>
>> -----Original Message-----
>> From: OSPF [mailto:ospf-bounces@ietf.org] On Behalf Of=20
>> internet-drafts@ietf.org
>> Sent: Thursday, May 4, 2017 3:28 PM
>> To: i-d-announce@ietf.org
>> Cc: ospf@ietf.org
>> Subject: [OSPF] I-D Action:
>> draft-ietf-ospf-segment-routing-extensions-13.txt
>>
>>
>> A New Internet-Draft is available from the on-line Internet-Drafts direc=
tories.
>> This draft is a work item of the Open Shortest Path First IGP of the IET=
F.
>>
>>           Title           : OSPF Extensions for Segment Routing
>>           Authors         : Peter Psenak
>>                             Stefano Previdi
>>                             Clarence Filsfils
>>                             Hannes Gredler
>>                             Rob Shakir
>>                             Wim Henderickx
>>                             Jeff Tantsura
>> 	Filename        : draft-ietf-ospf-segment-routing-extensions-13.txt
>> 	Pages           : 35
>> 	Date            : 2017-05-04
>>
>> Abstract:
>>      Segment Routing (SR) allows a flexible definition of end-to-end pat=
hs
>>      within IGP topologies by encoding paths as sequences of topological
>>      sub-paths, called "segments".  These segments are advertised by the
>>      link-state routing protocols (IS-IS and OSPF).
>>
>>      This draft describes the OSPF extensions required for Segment
>>      Routing.
>>
>>
>>
>> The IETF datatracker status page for this draft is:
>> https://datatracker.ietf.org/doc/draft-ietf-ospf-segment-routing-exte
>> n
>> sions/
>>
>> There are also htmlized versions available at:
>> https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extension
>> s
>> -13
>> https://datatracker.ietf.org/doc/html/draft-ietf-ospf-segment-routing
>> -
>> extensions-13
>>
>> A diff from the previous version is available at:
>> https://www.ietf.org/rfcdiff?url2=3Ddraft-ietf-ospf-segment-routing-ext
>> e
>> nsions-13
>>
>>
>> Please note that it may take a couple of minutes from the time of submis=
sion until the htmlized version and diff are available at tools.ietf.org.
>>
>> Internet-Drafts are also available by anonymous FTP at:
>> ftp://ftp.ietf.org/internet-drafts/
>>
>> _______________________________________________
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>
> .
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