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X-OriginatorOrg: ndzh.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Nov 2025 17:27:52.3284 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9d57d7ca-cefa-48bf-4b44-08de1e22fb2c X-MS-Exchange-CrossTenant-Id: d6c573f1-34ce-4e5a-8411-94cc752db3e5 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=d6c573f1-34ce-4e5a-8411-94cc752db3e5;Ip=[3.132.208.199];Helo=[us-east-2c.obx-outbound.inkyphishfence.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF00002310.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR08MB6309 Message-ID-Hash: BVV3VJHTEUVNL2E46WKDXDRVKLQL5TEM X-Message-ID-Hash: BVV3VJHTEUVNL2E46WKDXDRVKLQL5TEM X-MailFrom: shares@ndzh.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-idr.ietf.org-0; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.9rc6 Precedence: list Subject: =?utf-8?q?=5BIdr=5D_draft-lp-idr-bgp-ls-sr-policy-supplement_-_Interaction_b?= =?utf-8?q?etween_=22pure_backup_path=22_and_the_reverse_path_segment?= List-Id: Inter-Domain Routing Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --_000_DM8PR08MB7413BD76EA2C9C61D72A82E8B3C3ADM8PR08MB7413namp_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Question: How does the B-Flag interact on the segment list with the concepts of the reverse path segment from draft-ietf-idr-sr-policy-path-segement-14. See discussions below. Sue draft-ietf-idr-sr-policy-path-segment-14 defines This provides a forward and reverse path. SR Policy SAFI NLRI: Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Priority Policy Name Explicit NULL Label Policy (ENLP) Segment List Weight Path Segment Segment Segment ... Reverse Segment List Path Segment Segment Segment ... draft-lp-idr-bgp-ls-sr-policy-supplement-03 Defines new flags for the Segment list: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | | | | | |S|B| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: New Flags in the Flag Field of SR Segment List TLV * S-Flag: Indicates the segment list is in administrative shut state when set. The segment list may be shut by the administrator via CLI or other methods, and it is out of the scope of this document. * B-Flag: Indicates that the segment list is a pure backup path as specified in [I-D.ietf-pce-multipath] section 4.4 when set. When B-Flag is clear, it indicates it is the primary path that carries normal traffic >From draft-ietf-pce-multipath, we have two definitions: MULTIPATH-BACKUP TLV and MULTIPATH-OPPDIR-PATH. Below is the text from draft-ietf-pce-multipath This functionality is not part of the SR Policy Architecture [RFC9256], but is something optional that may be implemented for certain specialized use cases. One such use case is the P2MP SR Policy [I-D.draft-ietf-pce-sr-p2mp-policy]. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Backup Path Count | Flags |B| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Backup Path ID 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Backup Path ID 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Backup Path ID n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: MULTIPATH-BACKUP TLV format >From draft-ietf-pce-multipath ha the following opposite direction TLV? 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |L|N| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opposite Direction Path ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: MULTIPATH-OPPDIR-PATH TLV format --_000_DM8PR08MB7413BD76EA2C9C61D72A82E8B3C3ADM8PR08MB7413namp_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Question:

How does the B-Flag interact on the segment list with

the concepts of the reverse path segment from

draft-ietf-idr-sr-policy-path-segement-14.

 

See discussions below.

 

Sue

 

draft-ietf-idr-sr-policy-path-segment-14 defines

 

This provides a forward and reverse path.



       SR Policy SAFI NL= RI: <Distinguisher, Policy-Color, Endpoint>

          = ; Attributes: Tunnel Encaps Attribute (23)

          = ; Tunnel Type: SR Policy

          = ;     Binding SID

          = ;     Preference

          = ;     Priority

          = ;     Policy Name

          = ;     Explicit NULL Label Policy (ENLP)

         &n= bsp;     Segment List

          = ;         Weight<= /p>

          = ;         Path Segment

          = ;         Segment=

          = ;         Segment=

          = ;         ...

          = ;         Reverse Segment List=

          = ;             P= ath Segment

          = ;             S= egment

          = ;             S= egment

          = ;             .= ..

 

 

draft-lp-idr-bgp-ls-sr-policy-supplement-03

 

Defines new flags for the Segment list:

 

          = ;             0=             &nb= sp;      1

          = ;            &n= bsp;  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5

          = ;            &n= bsp; +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          = ;            &n= bsp; | | | | | | | | | |S|B|        = ; |

          = ;             &= nbsp;+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 

        Figure 1: New Fl= ags in the Flag Field of SR Segment List TLV

 

   *  S-Flag: Indicates the segment list is = in administrative shut state

      when set.  The segment = list may be shut by the administrator via

      CLI or other methods, and it= is out of the scope of this document.

 

   *  B-Flag: Indicates that the segment lis= t is a pure backup path as

      specified in [I-D.ietf-pce-m= ultipath] section 4.4 when set.  When

      B-Flag is clear, it indicate= s it is the primary path that carries

      normal traffic

 

 

From draft-ietf-pce-multipath, we have two definitions:

MULTIPATH-BACKUP TLV and MULTIPATH-OPPDIR-PATH. 

 

Below is the text from draft-ietf-pce-multipath<= /span>

 

   This functionality is not part of the SR = Policy Architecture

   [RFC9256], but is something optional that may = be implemented for

   certain specialized use cases.  One such = use case is the P2MP SR

   Policy [I-D.draft-ietf-pce-sr-p2mp-policy].

 

      0    &nb= sp;            =   1           &= nbsp;       2     &n= bsp;            = ; 3

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 = 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;       Type     &= nbsp;        |    &n= bsp;        Length   &nbs= p;        |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp; Backup Path Count       |  &nbs= p;          Flags  &= nbsp;        |B|

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;            =        Backup Path ID 1   &nbs= p;            &= nbsp;     |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;            =        Backup Path ID 2   &nbs= p;            &= nbsp;     |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;            =             ... = ;            &n= bsp;            = ;    |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;            =        Backup Path ID n   &nbs= p;            &= nbsp;     |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 

          = ;         Figure 3: MULTIPATH-BACKU= P TLV format

 

From draft-ietf-pce= -multipath ha the following opposite direction TLV?

 

      0   &nbs= p;            &= nbsp;  1          &n= bsp;        2    &nb= sp;            =   3

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 = 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;       Type     &= nbsp;        |    &n= bsp;        Length   &nbs= p;        |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;     Reserved      &nb= sp;     |       &nbs= p;     Flags       &= nbsp; |L|N|

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     &nb= sp;           Opposite Di= rection Path ID          =           |<= /p>

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-= +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 

          = ;       Figure 4: MULTIPATH-OPPDIR-PATH TLV f= ormat

 

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