Re: [Lsr] Link Data value for Multi-area links
Peter Psenak <ppsenak@cisco.com> Thu, 03 December 2020 10:30 UTC
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To: "Ketan Talaulikar (ketant)" <ketant@cisco.com>, "Acee Lindem (acee)" <acee=40cisco.com@dmarc.ietf.org>, "Van De Velde, Gunter (Nokia - BE/Antwerp)" <gunter.van_de_velde@nokia.com>, Alexander Okonnikov <alexander.okonnikov@gmail.com>, "Acee Lindem (acee)" <acee@cisco.com>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Thu, 03 Dec 2020 11:30:42 +0100
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Subject: Re: [Lsr] Link Data value for Multi-area links
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Hi Ketan, On 03/12/2020 11:26, Ketan Talaulikar (ketant) wrote: > Hi Peter, > > Please check inline below. > > -----Original Message----- > From: Peter Psenak <ppsenak@cisco.com> > Sent: 03 December 2020 15:48 > To: Ketan Talaulikar (ketant) <ketant@cisco.com>; Acee Lindem (acee) <acee=40cisco.com@dmarc.ietf.org>; Van De Velde, Gunter (Nokia - BE/Antwerp) <gunter.van_de_velde@nokia.com>; Alexander Okonnikov <alexander.okonnikov@gmail.com>; Acee Lindem (acee) <acee@cisco.com> > Cc: lsr@ietf.org > Subject: Re: [Lsr] Link Data value for Multi-area links > > Hi Ketan, > > On 03/12/2020 10:31, Ketan Talaulikar (ketant) wrote: >> Hello All, >> >> The text in RFC5185 for picking the neighbor’s IP Address or IfIndex >> for the link-data is indeed very odd and flies against how things are >> done for normal p2p links per RFC2328. >> >> The implementations that I am aware of do not really following this >> “decision” of RFC5185 and instead stick to RFC2328 architecture by >> picking the local IP address or IfIndex even for MADJ links. This way, >> a remote router cannot really distinguish between a normal P2P link or >> a MADJ – they look the same in the LSDB. >> >> While the neighbor IP address can be learnt via the source address >> used for the hello messages, there is really no simple way to learn >> the neighbor’s IfIndex for unnumbered links [1]. > > rfc8510? > [KT] Yes > >> >> So IMHO the RFC5185 is in error and we should fix this if we have >> consensus in the WG via a BIS as suggested by Acee. > > > I'm not convinced about the error. Nor about the need of the bis. > [KT] The question is why is RFC5185 not aligned with base OSPF RFC2328 on this aspect? What was the need for MADJ to have a reverse link-data information as compared to normal P2P links? it has been defined that way and I believe it works. Unless there is something that is broken, why would we need to change? thanks, Peter > > Thanks, > Ketan > > my 2c, > Peter > > >> >> Gunter, I am not getting into your other questions because of what >> I’ve mentioned above 😊 >> >> Thanks, >> >> Ketan >> >> [1] Note that over time we have introduced such mechanisms (RFC8510), >> but they have all been optional and not “base/required” behavior. >> >> *From:*Lsr <lsr-bounces@ietf.org> *On Behalf Of *Acee Lindem (acee) >> *Sent:* 30 November 2020 23:18 >> *To:* Van De Velde, Gunter (Nokia - BE/Antwerp) >> <gunter.van_de_velde@nokia.com>; Alexander Okonnikov >> <alexander.okonnikov@gmail.com>; Peter Psenak (ppsenak) >> <ppsenak@cisco.com>; Acee Lindem (acee) <acee@cisco.com> >> *Cc:* lsr@ietf.org >> *Subject:* Re: [Lsr] Link Data value for Multi-area links >> >> You are welcome to propose an alternate solution which could possibly >> be accepted as a BIS document. However, this is not something that can >> be simply changed in an Errata to reduce the complexity. >> >> Thanks, >> Acee >> >> *From: *Lsr <lsr-bounces@ietf.org <mailto:lsr-bounces@ietf.org>> on >> behalf of Gunter Van de Velde <gunter.van_de_velde@nokia.com >> <mailto:gunter.van_de_velde@nokia.com>> >> *Date: *Monday, November 30, 2020 at 12:21 PM >> *To: *"Acee Lindem (acee)" <acee=40cisco.com@dmarc.ietf.org >> <mailto:acee=40cisco.com@dmarc.ietf.org>>, Alexander Okonnikov >> <alexander.okonnikov@gmail.com >> <mailto:alexander.okonnikov@gmail.com>>, >> "Peter Psenak (ppsenak)" <ppsenak@cisco.com >> <mailto:ppsenak@cisco.com>> >> *Cc: *"lsr@ietf.org <mailto:lsr@ietf.org>" <lsr@ietf.org >> <mailto:lsr@ietf.org>> >> *Subject: *Re: [Lsr] Link Data value for Multi-area links >> >> The oddnes is that the architecture decision in RFC5185 to select >> remote-ip-address instead of local-ip-address for the ‘Link Data’ is >> making things much more complicated. >> >> I am surprised to see that using the remote-ip-address is seen as the >> ‘better’ choice as selecting local-ip-address. To me it seems as a >> worse choice. >> >> A question that was asked: How router will be able to match Link TLV >> (RFC 3630) to corresponding Link in Router LSA? >> >> Answer: >> >> For unnumbered links we can match Link TLV with Router TLV using the >> IfIndex when there is no stub type 3 link (=easy) >> >> For numbered: >> >> 1.we must first look if the there is a stub type 3 link >> >> 2.If stub type 3 exists, then the RFC3630 local ip address must be >> used to identify the correspond link within the router TLV to the >> neighbor >> >> 3.If the stub type 3 link did not exist in Router TLV link, then the >> maybe the link is unnumbered, and we try to match upon IfIndex… This >> may give a match or no match >> >> 4.If there is no match, then maybe the link is MADJ and we must use >> the >> RFC3630 remote IP address to match upon the Link Data >> >> 5.= over-complex. (If we used for RFC5185 ‘Link Data = local ip >> address’ then (2) would given answer directly) >> >> In addition, for a router it is much simpler to learn and advertise >> local-ip-address in Router LSAs then using a remote-ip-address. >> >> I also believe that if we want to search something in TEDB after >> receiving a TE Link TLV. How can we identify from the TE Link TLV if >> multi-area or not multi-area? If we can not, then how can we create >> the correct key? >> >> Looking at the above, the choice of using remote-ip-address for >> RFC5185 Link Data seems not the best design that we can do, and is >> adding OSPF complexity without benefits. >> >> Should this not be corrected in RFC5185 and simply use >> local-ip-address instead of the remote-ip-address for Multi-area Link >> Data and avoid the additional unnecessary complexity the current RFC for numbered links? >> >> Brgds, >> >> G/ >> >> *From:*Lsr <lsr-bounces@ietf.org <mailto:lsr-bounces@ietf.org>> *On >> Behalf Of *Acee Lindem (acee) >> *Sent:* Monday, November 30, 2020 18:01 >> *To:* Alexander Okonnikov <alexander.okonnikov@gmail.com >> <mailto:alexander.okonnikov@gmail.com>>; Peter Psenak (ppsenak) >> <ppsenak@cisco.com <mailto:ppsenak@cisco.com>> >> *Cc:* lsr@ietf.org <mailto:lsr@ietf.org> >> *Subject:* Re: [Lsr] Link Data value for Multi-area links >> >> Hi Alex, >> >> Multi-Area interface disambiguation is required to support the OSPF >> MIB as specified in RFC 4750. The table indexing doesn’t include the area. >> For example: >> >> -- OSPF Interface Table >> >> ospfIfTable OBJECT-TYPE >> >> SYNTAX SEQUENCE OF OspfIfEntry >> >> MAX-ACCESS not-accessible >> >> STATUS current >> >> DESCRIPTION >> >> "The OSPF Interface Table describes the interfaces >> >> from the viewpoint of OSPF. >> >> It augments the ipAddrTable with OSPF specific information." >> >> REFERENCE >> >> "OSPF Version 2, Appendix C.3 Router interface >> >> parameters" >> >> ::= { ospf 7 } >> >> ospfIfEntry OBJECT-TYPE >> >> SYNTAX OspfIfEntry >> >> MAX-ACCESS not-accessible >> >> STATUS current >> >> DESCRIPTION >> >> "The OSPF interface entry describes one interface >> >> from the viewpoint of OSPF. >> >> Information in this table is persistent and when this >> object >> >> is written the entity SHOULD save the change to >> non-volatile >> >> storage." >> >> INDEX { ospfIfIpAddress, ospfAddressLessIf } >> >> ::= { ospfIfTable 1 } >> >> Note that if you really want to support this optimally, you could use >> a separate subnet pre-area and have adjacencies on secondary >> addresses. My Redback/Ericsson implementation allowed for this. >> >> Thanks, >> >> Acee >> >> *From: *Lsr <lsr-bounces@ietf.org <mailto:lsr-bounces@ietf.org>> on >> behalf of Alexander Okonnikov <alexander.okonnikov@gmail.com >> <mailto:alexander.okonnikov@gmail.com>> >> *Date: *Monday, November 30, 2020 at 5:27 AM >> *To: *"Peter Psenak (ppsenak)" <ppsenak@cisco.com >> <mailto:ppsenak@cisco.com>> >> *Cc: *"lsr@ietf.org <mailto:lsr@ietf.org>" <lsr@ietf.org >> <mailto:lsr@ietf.org>> >> *Subject: *Re: [Lsr] Link Data value for Multi-area links >> >> Hi Peter, >> >> 30 нояб. 2020 г., в 12:56, Peter Psenak <ppsenak@cisco.com >> <mailto:ppsenak@cisco.com>> написал(а): >> >> Hi Alex, >> >> On 27/11/2020 13:49, Alexander Okonnikov wrote: >> >> Hi Peter, >> Which kind of ambiguity is meant? In case of numbered >> point-to-point each link has its own unique IP address, so there >> is no ambiguity. >> Per my understanding this problem has appeared due to follow >> reasons: >> 1) In old versions of the draft (up to -05) it was proposed that >> multi-area links are treated as unnumbered. ifIndex to be >> encoded in Link Data field, irrespectively whether interface has >> its own IP address (numbered) or borrow it (unnumbered); >> 2) From -06 to -08 multi-area links are still treated as >> unnumbered, but if interface is numbered, then IP address of the >> neighbor (rather than local one) to be encoded into Link Data, >> in order to make the link look like unnumbered; >> 3) In version -09 of the draft and in RFC 5185 itself there is >> no more mentions that multi-area link to be treated as >> unnumbered. Rather, another approach is used - if router's >> interface is numbered, then link is also numbered; if router's >> interface is unnumbered, then link is unnumbered. The rule that >> specifies omitting corresponding type 3 link is added. Mention >> of 'unnumbered' link is also removed from section 3 in RFC 5185. > >> Hence, in version -09 with removing unnumbered nature of >> multi-area links Link Data for numbered links had to be changed >> from Neighbor's IP address to own IP address, as it is specified >> in RFC 2328. From perspective of other routers this link can be >> treated as numbered or unnumbered, depending on configuration of >> neighbor's corresponding interface. >> >> >> you are free to advertise the link as unnumbered. RFC5185 is not >> mandating to send IP address really. >> >> The same valid for numbered ones. I.e. I'm free to advertise the link >> as numbered. This is straightforward when the link is numbered indeed. >> And if we would prefer to have deal with unnumbered interfaces, we >> would not need RFC 5185 (section 1.2). >> >> One question - how neighboring router will perform next-hop >> calculation (in case it needs to do so)? If neighbor is >> configured with numbered interface, it will treat Link Data as >> IP next hop, which will be its own IP interface address. >> Another question - how router will be able to match Link TLV >> (RFC 3630) to corresponding Link in Router LSA? For example, we >> want to calculate RSVP-TE LSP based on IGP metric (RFC 3785) and >> thus router needs to match IGP link to TE link. >> >> >> I don't believe you are going to do any traffic engineering over a >> multi-area adjacency. MADJ is there to address the OSPF route >> preference rules that may lead to sub-optimal routing. MADJ link is >> not advertised for TE purposes. >> >> Why not? We need multi-area configuration and at the same time we need >> ability to build intra-area RSVP-TE LSPs within each of areas. And >> what about calculating IP next hop? Which compatibility is meant in section 3? >> >> thanks, >> Peter >> >> Thank you. >> >> Thank you. >> >> 27 нояб. 2020 г., в 14:50, Peter Psenak <ppsenak@cisco.com >> <mailto:ppsenak@cisco.com>> написал(а): >> >> Alexander, >> >> On 26/11/2020 17:58, Alexander Okonnikov wrote: >> >> Hi WG, >> RFC 5185 says that Neighbor's IP address to be encoded >> into Link Data field. Per RFC 2328 router's own IP >> address to be encoded into Link Data. What is the reason >> to advertise neighbor's IP address for multi-area links >> and not local IP address? It seems like bug. Could >> someone comment on this? >> >> >> Advertising a neighbor address/ifindex helps to eliminate >> ambiguity in case of parallel point-to-point adjacencies. >> It's not perfect, but that's how it was specified. So it's >> not a bug. >> >> thanks, >> Peter >> >> Thanks in advance. >> _______________________________________________ >> Lsr mailing list >> Lsr@ietf.org <mailto:Lsr@ietf.org> >> https://www.ietf.org/mailman/listinfo/lsr >> > > >
- [Lsr] Link Data value for Multi-area links Alexander Okonnikov
- Re: [Lsr] Link Data value for Multi-area links Robert Raszuk
- Re: [Lsr] Link Data value for Multi-area links Peter Psenak
- Re: [Lsr] Link Data value for Multi-area links Alexander Okonnikov
- Re: [Lsr] Link Data value for Multi-area links Peter Psenak
- Re: [Lsr] Link Data value for Multi-area links Alexander Okonnikov
- Re: [Lsr] Link Data value for Multi-area links Acee Lindem (acee)
- Re: [Lsr] Link Data value for Multi-area links Van De Velde, Gunter (Nokia - BE/Antwerp)
- Re: [Lsr] Link Data value for Multi-area links Alexander Okonnikov
- Re: [Lsr] Link Data value for Multi-area links Acee Lindem (acee)
- Re: [Lsr] Link Data value for Multi-area links Acee Lindem (acee)
- Re: [Lsr] Link Data value for Multi-area links Aijun Wang
- Re: [Lsr] Link Data value for Multi-area links Ketan Talaulikar (ketant)
- Re: [Lsr] Link Data value for Multi-area links Ketan Talaulikar (ketant)
- Re: [Lsr] Link Data value for Multi-area links Peter Psenak
- Re: [Lsr] Link Data value for Multi-area links Ketan Talaulikar (ketant)
- Re: [Lsr] Link Data value for Multi-area links Peter Psenak
- Re: [Lsr] Link Data value for Multi-area links Gyan Mishra
- Re: [Lsr] Link Data value for Multi-area links Aijun Wang
- Re: [Lsr] Link Data value for Multi-area links Ketan Talaulikar (ketant)
- Re: [Lsr] Link Data value for Multi-area links Acee Lindem (acee)