Re: [OSPF] I-D Action: draft-ietf-ospf-segment-routing-extensions-13.txt
Peter Psenak <ppsenak@cisco.com> Thu, 11 May 2017 09:38 UTC
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Date: Thu, 11 May 2017 11:38:10 +0200
From: Peter Psenak <ppsenak@cisco.com>
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To: Shraddha Hegde <shraddha@juniper.net>, "internet-drafts@ietf.org" <internet-drafts@ietf.org>, "i-d-announce@ietf.org" <i-d-announce@ietf.org>
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Subject: Re: [OSPF] I-D Action: draft-ietf-ospf-segment-routing-extensions-13.txt
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Hi Shraddha, On 11/05/17 11:30 , Shraddha Hegde wrote: > 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? - Intra-area route, where the downstream neighbor is not the originator or the prefix - Inter-area prefixes, for which the downstream neighbor is not the originator or the prefix - External prefix for which the downstream neighbor is not the originator or the prefix - Inter-area prefixes, where originator is not advertising Extended Prefix TLV - External prefix , where originator is not advertising Extended Prefix TLV thanks, Peter > >> "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 > not have many scenarios to list. > > Rgds > Shraddha > -----Original Message----- > From: Peter Psenak [mailto:ppsenak@cisco.com] > Sent: Thursday, May 11, 2017 2:46 PM > To: Shraddha Hegde <shraddha@juniper.net>; internet-drafts@ietf.org; i-d-announce@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 >> 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. > > when SRMS advertises the SID, it can not set the NP-Flag, so we can not apply 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 >> 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 as >> 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 SRMS, 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; >> i-d-announce@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 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:ospf-bounces@ietf.org] On Behalf Of >>> 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 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-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=draft-ietf-ospf-segment-routing-ext >>> e >>> 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/ >>> >>> _______________________________________________ >>> OSPF mailing list >>> OSPF@ietf.org >>> https://www.ietf.org/mailman/listinfo/ospf >>> >>> _______________________________________________ >>> OSPF mailing list >>> OSPF@ietf.org >>> https://www.ietf.org/mailman/listinfo/ospf >>> . >>> >> >> . >> > > . >
- [OSPF] I-D Action: draft-ietf-ospf-segment-routin… internet-drafts
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Ketan Talaulikar Talaulikar (ketant)
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Peter Psenak
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Erik Auerswald
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Peter Psenak
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Shraddha Hegde
- Re: [OSPF] I-D Action: draft-ietf-ospf-segment-ro… Peter Psenak