Re: [Lsr] Enhancement related to Area Leader Sub-TLV

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Tue, 28 May 2019 15:19 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: Huaimo Chen <hchen@futurewei.com>, "tony.li@tony.li" <tony.li@tony.li>
CC: "lsr@ietf.org" <lsr@ietf.org>
Thread-Topic: Enhancement related to Area Leader Sub-TLV
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Date: Tue, 28 May 2019 15:19:09 +0000
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Subject: Re: [Lsr] Enhancement related to Area Leader Sub-TLV
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Huaimo -

It is highly undesirable that there only be one Area Leader sub-TLV advertisement. The latest version of the draft (V2) highlights this. Please see https://tools.ietf.org/html/draft-ietf-lsr-dynamic-flooding-02#section-6.8.10

You have also not responded to Tony's point that we do not expect ALL nodes to advertise Area Leader Sub-TLV - which means the savings you calculate below isn't real.

   Les


From: Lsr <lsr-bounces@ietf.org> On Behalf Of Huaimo Chen
Sent: Monday, May 27, 2019 7:50 PM
To: tony.li@tony.li
Cc: lsr@ietf.org
Subject: Re: [Lsr] Enhancement related to Area Leader Sub-TLV


Hi Tony,



    Thank you for your explanations.


    After moving one byte for the priority from Area Leader Sub-TLV to Dynamic Flooding Sub-TLV, only one Area Leader Sub-TLV is advertised. For an area with N nodes supporting both centralized and distributed mode, my understanding is below.

    Before moving, each of N nodes may advertise an Area Leader Sub-TLV and a Dynamic Flooding Sub-TLV. After moving, only the leader node advertises a (Updated) Area Leader Sub-TLV. Thus (N - 1) Area Leader Sub-TLVs are saved, which use space of (N-1)*S1 bytes, where S1 is the size of Area Leader Sub-TLV. Each of N nodes may advertise a (Updated) Dynamic Flooding Sub-TLV, which has one extra byte for the priority. Thus N bytes are used.

    The saving on space after moving should be (N-1)*S1 - N. S1 is 4 in IS-IS; S1 is 8 in OSPF.
For N = 1000 and IS-IS, the saving is (1000-1)*4 - 1000 = 2996 (bytes)
For N = 1000 and OSPF, the saving is (1000-1)*8 - 1000 = 6992 (bytes)

Best Regards,
Huaimo
________________________________
From: Tony Li <tony1athome@gmail.com<mailto:tony1athome@gmail.com>> on behalf of tony.li@tony.li<mailto:tony.li@tony.li> <tony.li@tony.li<mailto:tony.li@tony.li>>
Sent: Friday, May 24, 2019 4:56 PM
To: Huaimo Chen
Cc: lsr@ietf.org<mailto:lsr@ietf.org>
Subject: Re: Enhancement related to Area Leader Sub-TLV


Hi Huaimo,

Thank you for your proposal.

The area leader sub-tlv is only advertised by systems that are willing to be area leader.  Presumably, that's not necessarily all of the ones who support dynamic flooding.  Thus, what you're proposing moves one byte from one TLV into another TLV that will be more commonly used. So your proposal actually consumes more LSP space.

The intention here is that the candidates for area leader advertise the Area Leader Sub-TLV.  All nodes that support dynamic flooding would advertise the Dynamic Flooding Sub-TLV.
Since the priority is part of the Area Leader election, it makes sense for it to be part of the Area Leader Sub-TLV.

Regards,
Tony

p.s. IS-IS does not depend on word-alignment, so we typically do not leave reserved bytes in our TLV formats. OSPF is a different kettle of fish... :-)



On May 24, 2019, at 1:44 PM, Huaimo Chen <hchen@futurewei.com<mailto:hchen@futurewei.com>> wrote:

Hi Tony,

     An enhancement related to Area Leader Sub-TLV is briefed below for discussions.  A .pdf file is attached in the case that the formats below are messed up.

The leader of an area advertises an Area Leader Sub-TLV to indicate/instruct whether centralized or distributed mode is to be used by all the nodes in the area (Algorithm = 0: centralized mode; Algorithm = N (N>0): distributed mode and N is the algorithm to be used by every node to compute flooding topology).


Currently for IS-IS, IS-IS Area Leader Sub-TLV below is used by each of the nodes to advertise its priority for becoming the leader
    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    | Priority      |   Algorithm   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     (Current) IS-IS Area Leader Sub-TLV


It seems hard to understand that every node uses an Area Leader Sub-TLV to advertise its priority for becoming the leader, and at the same time to indicate/instruct whether centralized or distributed mode is to be used by all the nodes in the area.


When every node advertises an Area Leader Sub-TLV, only one for indication/instruction for flooding reduction mode is used, and all the others are not used, which consume space and processing time.


An enhancement is to let every node advertise its priority for becoming the leader and the algorithms that it supports though using a Dynamic Flooding Sub-TLV, and only the leader advertise the indication for the flooding reduction mode. To achieve this, some changes to the two Sub-TLVs and the texts related to the Sub-TLVs should be made.


For IS-IS, IS-IS Area Leader Sub-TLV is updated as follows (Priority is removed)
    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      |   Algorithm   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                   (Updated) IS-IS Area Leader Sub-TLV


The Priority is added into IS-IS Dynamic Flooding Sub-TLV. The current IS-IS Dynamic Flooding Sub-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    | Algorithm...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   (Current) IS-IS Dynamic Flooding Sub-TLV


is changed to:
    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    | Priority       |Algorithm...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   (Updated) IS-IS Dynamic Flooding Sub-TLV


Similarly for OSPF, the current OSPF Area Leader Sub-TLV below
       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Priority   |   Algorithm   |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                   (Current) OSPF Area Leader Sub-TLV
is changed to
       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   |   Algorithm   |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                   (Updated) OSPF Area Leader Sub-TLV


The current OSPF Dynamic Flooding Sub-TLV below
       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Algorithm ... |                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      (Current) OSPF Dynamic Flooding Sub-TLV
is changed to
       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Priority   | Algorithm ... |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      (Updated) OSPF Dynamic Flooding Sub-TLV


Best Regards,
Huaimo

<EnhanceOnAdvertisePriority4Leader.pdf>