Subject: [OSPF] [OSPFv3-SR] Regarding LAN Adj-SID/Label description

From: Veerendranatha Reddy Vallem <[email-masked]>
Date: Tue, 29 Nov 2016 02:06:34 +0000

Dear Authors,

As per draft, for LAN SID Sub-TLV,

7.2.  LAN Adj-SID Sub-TLV

   The LAN Adj-SID is an optional Sub-TLV of the Router-Link TLV.  It
   MAY appear multiple times in the Router-Link TLV.  It is used to
   advertise a SID/Label for an adjacency to a non-DR neighbor on a
   broadcast or NBMA network.

    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             |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |     Flags     |     Weight    |            Reserved           |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                           Neighbor ID                         |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                    SID/Label/Index (variable)                 |

   +---------------------------------------------------------------+

"LAN SID is used for non-DR neighbors." We cannot use this Sub TLV to provide SID for DR router (Neighbor ID is DR's router id in this TLV) ?
It means we need to include "Adj_SID Sub TLV for DR neighbor" and LAN Adj-SID for other neighbors (including BDR)  in the network while advertising Adj- SID in Router Link TLV for LAN?
Can you please provide clarity for this sub TLV.

Regards,
Veerendranath

---

From: Peter Psenak <[email-masked]>
Date: Tue, 29 Nov 2016 09:01:45 +0100

Veerendranath,

please see inline:

On 29/11/16 03:06 , Veerendranatha Reddy Vallem wrote:
>     MAY appear multiple times in the Router-Link TLV. *It is used to*
>
> *   advertise a SID/Label for an adjacency to a non-DR neighbor on a*
>
> *   broadcast or NBMA network.*
>
> **
>
>      0                   1                   2                   3
>
> **
> “LAN SID is used for non-DR neighbors.” We cannot use this Sub TLV to
> provide SID for DR router (Neighbor ID is DR’s router id in this TLV) ?

No.

>
> It means we need to include “Adj_SID Sub TLV for DR neighbor” and LAN
> Adj-SID for other neighbors (including BDR)  in the network while
> advertising Adj- SID in Router Link TLV for LAN?

yes, that is correct.

8.4.2.  Adjacency SID on Broadcast or NBMA Interfaces

    Broadcast or NBMA networks in OSPFv3 are represented by a star
    topology where the Designated Router (DR) is the central point to
    which all other routers on the broadcast or NBMA network connect.  As
    a result, routers on the broadcast or NBMA network advertise only
    their adjacency to the DR.  Routers that do not act as DR do not form
    or advertise adjacencies with each other.  They do, however, maintain
    a 2-Way adjacency state with each other and are directly reachable.

Psenak, et al.             Expires May 1, 2017                 [Page 31]

Internet-Draft    OSPFv3 Extensions for Segment Routing     October 2016

    When Segment Routing is used, each router on the broadcast or NBMA
    network MAY advertise the Adj-SID for its adjacency to the DR using
    Adj-SID Sub-TLV as described in Section 7.1.

    SR capable routers MAY also advertise an Adj-SID for other neighbors
    (e.g.  BDR, DR-OTHER) on the broadcast or NBMA network using the LAN
    ADJ-SID Sub-TLV as described in Section 7.2.

thanks,
Peter