Re: [Lsr] RFC8401 - Question on BIER TLV leaking from one level to the other
"Xiejingrong (Jingrong)" <xiejingrong@huawei.com> Thu, 16 January 2020 09:53 UTC
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From: "Xiejingrong (Jingrong)" <xiejingrong@huawei.com>
To: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>, Senthil Dhanaraj <senthil.dhanaraj.ietf@gmail.com>, Antoni Przygienda <prz@juniper.net>, "aldrin.ietf@gmail.com" <aldrin.ietf@gmail.com>, "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>
CC: BIER WG <bier@ietf.org>, Liangyanrong <liangyanrong@huawei.com>, dongjiajia <dongjiajia@huawei.com>, "lsr@ietf.org" <lsr@ietf.org>
Thread-Topic: RFC8401 - Question on BIER TLV leaking from one level to the other
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Date: Thu, 16 Jan 2020 09:53:30 +0000
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Subject: Re: [Lsr] RFC8401 - Question on BIER TLV leaking from one level to the other
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Hi Les, Thanks for the clarification. Would expect the Errata from Senthil as well. Jingrong From: Les Ginsberg (ginsberg) [mailto:ginsberg@cisco.com] Sent: Thursday, January 16, 2020 12:41 AM To: Xiejingrong (Jingrong) <xiejingrong@huawei.com>; Senthil Dhanaraj <senthil.dhanaraj.ietf@gmail.com>; Antoni Przygienda <prz@juniper.net>; aldrin.ietf@gmail.com; Jeffrey (Zhaohui) Zhang <zzhang@juniper.net> Cc: BIER WG <bier@ietf.org>; Liangyanrong <liangyanrong@huawei.com>; dongjiajia <dongjiajia@huawei.com> Subject: RE: RFC8401 - Question on BIER TLV leaking from one level to the other Jingrong – I had to look at this twice because of the long interval since the last email on this thread. Inline. From: Xiejingrong (Jingrong) <xiejingrong@huawei.com<mailto:xiejingrong@huawei.com>> Sent: Tuesday, January 14, 2020 11:15 PM To: Les Ginsberg (ginsberg) <ginsberg@cisco.com<mailto:ginsberg@cisco.com>>; Senthil Dhanaraj <senthil.dhanaraj.ietf@gmail.com<mailto:senthil.dhanaraj.ietf@gmail.com>>; Antoni Przygienda <prz@juniper.net<mailto:prz@juniper.net>>; aldrin.ietf@gmail.com<mailto:aldrin.ietf@gmail.com>; Jeffrey (Zhaohui) Zhang <zzhang@juniper.net<mailto:zzhang@juniper.net>> Cc: BIER WG <bier@ietf.org<mailto:bier@ietf.org>>; Liangyanrong <liangyanrong@huawei.com<mailto:liangyanrong@huawei.com>>; dongjiajia <dongjiajia@huawei.com<mailto:dongjiajia@huawei.com>> Subject: RE: RFC8401 - Question on BIER TLV leaking from one level to the other Hi Les, Thank you very much for the clarification. I am curious if the text about N flag also need to change when BIER TLV is leaking from one level to another. RFC7794 says in section 2.1 about N-flag: “Set when the prefix identifies the advertising router”. [Les:] RFC7794 also says: “The flag MUST be preserved when leaked between levels.” The identity of the originating router can be obtained from the source Router ID sub-TLV defined in https://tools.ietf.org/html/rfc7794#section-2.2 In the case when a BIER TLV (prefix=Prefix-ABR) is leaking by an ABR router from Level-1 to Level-2, the advertising router is ABR and the prefix is Prefix-ABR(a prefix bound to a Level-1 interface of ABR), so the N-flag need to be set. In the case when a BIER TLV (prefix=Prefix-A) is leaking by an ABR router from Level-1 to Level-2, the advertising router is ABR but the prefix is Prefix-A(a prefix bound to a interface of router-A), so the N-flag need to be cleared. Is the understanding correct ? Would anyone please raise an Errata about this defect in the RFC ? I can also do that if needed. [Les:] To be sure we are on the same page, the only Errata is the one mentioned below regarding the R flag. There is no issue regarding the N flag. I believe Senthil indicated he would create an Errata for that but it appears that this never happened. Les Best regards, Jingrong From: BIER [mailto:bier-bounces@ietf.org] On Behalf Of Les Ginsberg (ginsberg) Sent: Saturday, April 13, 2019 4:24 AM To: Senthil Dhanaraj <senthil.dhanaraj.ietf@gmail.com<mailto:senthil.dhanaraj.ietf@gmail.com>>; Antoni Przygienda <prz@juniper.net<mailto:prz@juniper.net>>; aldrin.ietf@gmail.com<mailto:aldrin.ietf@gmail.com>; Jeffrey (Zhaohui) Zhang <zzhang@juniper.net<mailto:zzhang@juniper.net>> Cc: BIER WG <bier@ietf.org<mailto:bier@ietf.org>> Subject: Re: [Bier] RFC8401 - Question on BIER TLV leaking from one level to the other Senthil – There is no such thing as a “BIER-ISIS extension TLV”. There is only the “BIER Info” sub-TLV(sic) which is carried in a Prefix Reachability TLV (one of TLVs 135, 235, 236, and 237). Therefore the Prefix-Attribute sub-TLV can and should be present in such a TLV as well. See https://tools.ietf.org/html/rfc8401#section-4.2 The only minor issue here is that the RFC says: o When the Prefix Attributes Flags sub-TLV [RFC7794] is present, the N flag MUST be set and the R flag MUST NOT be set. In cases where the prefix is leaked the R flag will be set. The text is a holdover from early versions where we had prohibited leaking. In cases where the prefix is leaked the R flag will be set. I suppose this deserves an Errata. I thought this issue had been discussed and addressed – but I couldn’t find any relevant email and clearly the published text has a flaw. Sigh… Les From: Senthil Dhanaraj <senthil.dhanaraj.ietf@gmail.com<mailto:senthil.dhanaraj.ietf@gmail.com>> Sent: Thursday, April 11, 2019 11:03 PM To: Les Ginsberg (ginsberg) <ginsberg@cisco.com<mailto:ginsberg@cisco.com>>; Antoni Przygienda <prz@juniper.net<mailto:prz@juniper.net>>; aldrin.ietf@gmail.com<mailto:aldrin.ietf@gmail.com>; Jeffrey (Zhaohui) Zhang <zzhang@juniper.net<mailto:zzhang@juniper.net>> Cc: BIER WG <bier@ietf.org<mailto:bier@ietf.org>> Subject: RFC8401 - Question on BIER TLV leaking from one level to the other Hi Authors, When ABR leaks the Prefix (& BIER TLVs) from one level to another, the LSP contains both the ABR's local prefix and the other prefix'es which are re-advertised from one level to the other. Nodes receiving such an LSP should be able to identify the Prefix (& BIER TLV) that is originally local to the ABR from the other inter (re-advertised) prefix'es. Unlike SR-ISIS extensions TLV, BIER-ISIS extension TLVs do not have N/R flags. Hence the only way to identify the prefix type (local or re-advertised) is by having the ABR advertise the "IPv4/IPv6 Extended Reachability Attribute Flags sub-TLV - RFC7794" whenever it leaks the BIER TLVs from one level to another. Is my understanding correct? Ref from - RFC 7794 - 2.1<https://tools.ietf.org/html/rfc7794#section-2.1>. IPv4/IPv6 Extended Reachability Attribute Flags 0 1 2 3 4 5 6 7... +-+-+-+-+-+-+-+-+... |X|R|N| ... +-+-+-+-+-+-+-+-+... R-Flag: Re-advertisement Flag (Bit 1) Set when the prefix has been leaked from one level to another (upwards or downwards). Thanks, Senthil
- Re: [Lsr] RFC8401 - Question on BIER TLV leaking … Xiejingrong (Jingrong)
- Re: [Lsr] RFC8401 - Question on BIER TLV leaking … Xiejingrong (Jingrong)
- Re: [Lsr] RFC8401 - Question on BIER TLV leaking … Xiejingrong (Jingrong)
- Re: [Lsr] RFC8401 - Question on BIER TLV leaking … Les Ginsberg (ginsberg)
- Re: [Lsr] RFC8401 - Question on BIER TLV leaking … Xiejingrong (Jingrong)