Peter,
It is clearly specified that ABR originating prefixes from other areas 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 advertisements as
well.
" 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 it does
not cover the
Case of re-distributed prefixes for mapping server advertisements.
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 as
described in section 2.1 of [RFC7684] then PHP MUST not be done"
Rgds
Shraddha
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Wednesday, May 10, 2017 12:33 PM
To: Shraddha Hegde <[email protected]>; [email protected];
[email protected]
Cc: [email protected]
Subject: Re: [OSPF] I-D Action:
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 standardization.
>
> 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
> 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 packet
> to ABR, It does not work since the inner labels gets exposed at the 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 distinguish
between the two based on the A-flag in the Extended Prefix TLV as specified 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:[email protected]] On Behalf Of
> [email protected]
> Sent: Thursday, May 4, 2017 3:28 PM
> To: [email protected]
> Cc: [email protected]
> 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
> directories.
> This draft is a work item of the Open Shortest Path First IGP of the IETF.
>
> 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 paths
> 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-exten
> sions/
>
> There are also htmlized versions available at:
> https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extensions
> -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=draft-ietf-ospf-segment-routing-exte
> nsions-13
>
>
> Please note that it may take a couple of minutes from the time of submission
> 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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