Re: [Idr] Regd. https://datatracker.ietf.org/doc/draft-mohanty-idr-secondary-label/

Igor Malyushkin <gmalyushkin@gmail.com> Sat, 12 August 2023 12:39 UTC

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From: Igor Malyushkin <gmalyushkin@gmail.com>
Date: Sat, 12 Aug 2023 16:38:48 +0400
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To: Robert Raszuk <robert@raszuk.net>
Cc: "Satya Mohanty (satyamoh)" <satyamoh=40cisco.com@dmarc.ietf.org>, "idr@ietf.org" <idr@ietf.org>, "RAMADENU, PRAVEEN" <pr9637@att.com>
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Subject: Re: [Idr] Regd. https://datatracker.ietf.org/doc/draft-mohanty-idr-secondary-label/
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Hello, Robert, Satya,

Using different CLUSTER_IDs for inline RRs at the same hierarchy level is
common. Especially when there is a labeled unicast underneath. Although, I
don't understand why two RRs should be clients to each other instead of
regular non-client peers.

For PD#1, it is possible to signal LU addresses of PE1, PE2, and both RRs
and use them as NHs for VPN prefixes. In this case for labeled unicast
prefixes a per-prefix label allocation mode completely solves the problem.
For VPN sessions RRs do not apply next-hop-self but act as classical RRs
(or even can be unaware of any VPN sessions at all). Classical seamless
MPLS approach. With the different CLUSTER_IDs, PIC between the RRs can be
maintained also.

If we talk about Option B, the solution with LU does not obviously work,
but there are several approaches to cope with scaling problems, Option A/B,
and Option B/C (draft-zzhang-bess-vpn-option-bc-00). The latest is the new
draft that combines a two-labeled approach but does not require new path
attributes.

For PD#2, here I agree with Robert that it is strange to use internal BGP
paths instead of external ones for PIC in that case. What if the ISP1 box
goes down? All the traffic will go to the ISP2 box from both PEs anyway.
Isn't it wise not to use internal BGP paths for a link failure? Actually,
we don't even differentiate a link down even from a node failure. But we
are trying to apply different FFR technics there.

Also, for a possible loop, does not NFRR from the MNA framework solve this
issue at the transport level?

My 2 cents.


сб, 12 авг. 2023 г. в 15:45, Robert Raszuk <robert@raszuk.net>:

> Satya,
>
> *Reg PD#1: *
>
> Problem described as PD#1 arises by violation of RFC4456 rules. When your
> RRs are part of the same cluster (and here they clearly are) it is
> mandatory to use the same CLUSTER_ID on both route reflectors. That will
> prevent any reflected routes to get accepted by the other RR client.
>
>    Both these RRs are also clients of each other and advertise VPN routes to each other with the
>    next-hop set to the peering address.
>
>
> Please do not invent a bandage to heal wounds which should not be self
> made in the first place. PD#1 as described is a misconfiguration.
>
> *Reg PD#2:*
>
> You say:
>
> >  Failure scenario 2 (FS#2) The links from ISP1 to PE1 and PE2 are down
> >  at the same time;
>
> If those two links go down in the same time both PEs should notice it
> (optics or BFD) and apply PIC accordingly. PIC on PE1 should result in
> shifting traffic to ISP2. So should PIC action on PE2.
>
> As with PIC the FIB rewrite is prefix independent so no loop should form.
>
> As you said both ISPs advertise identical set of routes: "Both ISPs
> advertise the same 700k prefixes/"
>
> Only in a situation when you would apply eiBGP multipath there could be
> some micr-loop.
>
> PIC should be smart and ignore IBGP paths (if their local pref is
> preferred in steady state) if local EBGP paths exist to heal data plane
> during the fast repair. Tnen BGP will converge to the policy
> aligned selection of exist.
>
> Kind regards,
> Robert
>
>
> On Thu, Jul 27, 2023 at 9:36 AM Satya Mohanty (satyamoh) <satyamoh=
> 40cisco.com@dmarc.ietf.org> wrote:
>
>> Hi Keyur and the chairs,
>>
>>
>>
>> Towards the end of my IETF presentation, the audio was coming garbled at
>> my end and not at all coherent.
>>
>> I went over the recording today. I am replying to the two
>> questions/observations.
>>
>>
>>
>> 1)  Suggestion was given to use another label mode i.e., per-prefix
>> (per-vrf does not apply here).  However, using per-prefix label allocation
>> would result in the inline RRs/ASBRs exhausting their label threshold
>> (platform dependent  very quickly as the route scale increases (platform
>> dependent upper-limit). Therefore, using per-prefix label allocation was
>> ruled out in this deployment after being given due consideration.
>>
>>
>>
>> Cisco IOS-XR supports the per-nexthop-recvd-label mode for some-time now
>> in Option-B ASBR and RR with nh-self use-cases, precisely for this reason.
>> I believe other vendors has an equivalent mode. Idea is to take advantage
>> of the optimal label allocation by this mode and simultaneously ensure fast
>> convergence via BGP PIC.
>>
>>
>>
>> 2) Regarding the suggestion of not using the proposed attribute, the
>> original thought was to use tunnel-encaps attribute. The problem that I saw
>> is that the tunnel-encaps can have many sub-tlvs for different purposes,
>> and if we wanted to restrict the advertisement of the secondary label to
>> routers that do not need it, it will not be that easy as those same routers
>> may need some other TLVs present in that same tunnel-encaps attribute. But,
>> we do look forward to getting your inputs/suggestions on this as you
>> indicated.
>>
>>
>>
>> Thanks.
>>
>>
>>
>> Best Regards,
>>
>> --Satya
>>
>>
>>
>>
>>
>>
>>
>> *From: *Idr <idr-bounces@ietf.org> on behalf of Satya Mohanty (satyamoh)
>> <satyamoh=40cisco.com@dmarc.ietf.org>
>> *Date: *Tuesday, July 11, 2023 at 9:44 PM
>> *To: *Dongjie (Jimmy) <jie.dong=40huawei.com@dmarc.ietf.org>,
>> idr@ietf.org <idr@ietf.org>, MEANS, ISRAEL L <im8327@att.com>, RAMADENU,
>> PRAVEEN <pr9637@att.com>
>> *Cc: *idr-chairs@ietf.org <idr-chairs@ietf.org>
>> *Subject: *Re: [Idr] Call for IETF 117 IDR agenda items
>>
>> Hi Jie,
>>
>>
>>
>> We would like to request a slot of 10 minutes to present the following
>> draft. Tuesday slot is preferable.
>>
>> https://datatracker.ietf.org/doc/draft-mohanty-idr-secondary-label/
>>
>>
>>
>> Thanks,
>>
>> --Satya
>>
>>
>>
>> *From: *Idr <idr-bounces@ietf.org> on behalf of Dongjie (Jimmy)
>> <jie.dong=40huawei.com@dmarc.ietf.org>
>> *Date: *Tuesday, June 27, 2023 at 3:57 PM
>> *To: *idr@ietf.org <idr@ietf.org>
>> *Cc: *idr-chairs@ietf.org <idr-chairs@ietf.org>
>> *Subject: *[Idr] Call for IETF 117 IDR agenda items
>>
>> Dear all,
>>
>>
>>
>> The draft agenda of IETF 117 is available at
>> https://datatracker.ietf.org/meeting/117/agenda. The IDR sessions are
>> scheduled as below:
>>
>>
>>
>> - Monday Session II  13:00 - 15:00 (local time)  Plaza B
>>
>>
>>
>> - Thursday Session IV 17:00 – 18:00 (local time)  Continental 4
>>
>>
>>
>> Please start to send any IDR agenda item request to me and CC the chairs (
>> idr-chairs@ietf.org). Please include the name of the person who will be
>> presenting, and the estimate time you'll need (including Q/A).
>>
>>
>>
>> If you plan to make a presentation, please keep in mind the IDR
>> tradition, "no Internet Draft - no time slot". You should also plan to send
>> your slides to me and CC the chairs no later than 24 hours prior to the IDR
>> session, though earlier is better. Please number your slides for the
>> benefit of remote attendees. By default your slides will be converted to
>> PDF and presented from the PDF.
>>
>>
>>
>> Potential presenters may want to take a look at the checklist for
>> presenting at IDR:
>>
>>
>>
>>
>> https://trac.tools.ietf.org/wg/idr/trac/wiki/Checklist%20for%20presenting%20at%20an%20IDR%20meeting
>>
>>
>>
>> Best regards,
>>
>> Jie
>> _______________________________________________
>> Idr mailing list
>> Idr@ietf.org
>> https://www.ietf.org/mailman/listinfo/idr
>>
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