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Re: [Idr] Few questions about Segment Routing extensions for BGP LS (draft-ietf-idr-bgp-ls-segment-routing-ext)

"Wanghaibo (Rainsword)" <rainsword.wang@huawei.com> Thu, 22 July 2021 08:12 UTC

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From: "Wanghaibo (Rainsword)" <rainsword.wang@huawei.com>
To: Boris Hassanov <bhassanov=40yahoo.com@dmarc.ietf.org>, IDR List <idr@ietf.org>
Thread-Topic: [Idr] Few questions about Segment Routing extensions for BGP LS (draft-ietf-idr-bgp-ls-segment-routing-ext)
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Date: Thu, 22 Jul 2021 08:12:20 +0000
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Subject: Re: [Idr] Few questions about Segment Routing extensions for BGP LS (draft-ietf-idr-bgp-ls-segment-routing-ext)
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Hi Boris,

2)  draft-ietf-idr-bgp-ls-segment-routing-ext-18 has two types of labels TLV: SID/Label TLV type 1161 and Prefix SID  TLV type 1158.  I checked several vendors implementations of BGP-LS, all of them use only Prefix SID TLV.

BGP-LS information come from ISIS or OSPF. The Prefix-SID can indicate a node. But there is no separate Node-SID defined now.


Regards,
Haibo

From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of Boris Hassanov
Sent: Wednesday, July 21, 2021 5:55 PM
To: IDR List <idr@ietf.org>
Subject: [Idr] Few questions about Segment Routing extensions for BGP LS (draft-ietf-idr-bgp-ls-segment-routing-ext)

Hi all,

1) Need an advice, I might be missing something but I see that Anycasi SID (3333 in the example below)  is in BGP-LS update as regular Prefix SID TLV:

 Path Attribute - BGP-LS Attribute

            Flags: 0x80, Optional, Non-transitive, Complete

                1... .... = Optional: Set

                .0.. .... = Transitive: Not set

                ..0. .... = Partial: Not set

                ...0 .... = Extended-Length: Not set

                .... 0000 = Unused: 0x0

            Type Code: BGP-LS Attribute (29)

            Length: 12

            Link State

                Prefix SID TLV

                    Type: 1158

                    Length: 8

                    Flags: 0x40, Node-SID (N)

                        0... .... = Re-advertisement (R): Not set

                        .1.. .... = Node-SID (N): Set

                        ..0. .... = No-PHP (P): Not set

                        ...0 .... = Explicit-Null (E): Not set

                        .... 0... = Value (V): Not set

                        .... .0.. = Local (L): Not set

                    Algorithm: 0

                    SID/Index: 3333

Here is confusion, how, let's say, a controller, which receives such BGP-LS update, could  distinguish it from regular Prefix/Node SID?

Unfortunately draft-ietf-idr-bgp-ls-segment-routing-ext-18 does not clarify this issue because it only describes Prefix SID TLV type 1158. Any suggestions?

2)  draft-ietf-idr-bgp-ls-segment-routing-ext-18 has two types of labels TLV: SID/Label TLV type 1161 and Prefix SID  TLV type 1158.  I checked several vendors implementations of BGP-LS, all of them use only Prefix SID TLV.
Why the draft does not have some conditions or clarifications when to use SID/Label TLV and when Prefix SID TLV?

Thank you.

SY,
Boris

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