Subject: [pim] bi-dir features [I-D ACTION:draft-ietf-mboned-routingarch-00.txt]

From: Pekka Savola <[email-masked]>
Date: Sat, 30 Apr 2005 10:11:38 +0300 (EEST)

(redirecting the mboned thread to pim list; we're discussing two open 
bi-dir pim issues in draft-ietf-mboned-routingarch-00.txt)

On Thu, 28 Apr 2005, Dino Farinacci wrote:
>>> [Bi-directional PIM]
>>>     Bi-directional PIM (see Section 2.1.3) was designed with faster
>>>     multicast convergence in mind, and if fast failover is required, it
>>>     may seem like an attractive solution.
>
>    I would argue that DF-election is slower than RPF which is used in ASM
>    and SSM. Since both DF-election and RPF are triggered by a unicast routing
>    table change, the former requires multiple packet exchanges on all LAN
>    interfaces before convergence is achieved where the later is just an
>    internal router change to the multicast routing table entries.

Well, at least Toerless argued bi-dir PIM as ""establish and 
fast-converge of loop-free rp-rooted bidirectional spanning trees 
within a network", but maybe I misunderstood or this would not have 
full consensus.

But I don't care about this either way -- I just want to have 1-2 
paragraph short summary about Bi-dir PIM compared to PIM-SM.  The two 
subsections, as they currently are, are below.  I'm open to any 
suggestions as how to reword them!

.........

2.1.3  Bi-directional PIM

    Bi-directional PIM [I-D.ietf-pim-bidir] aims to offer streamlined
    PIM-SM operation, without data-driven events and data-encapsulation,
    inside a PIM-SM domain.  The usage of bi-dir PIM may be on the
    increase especially inside sites leveraging multicast.

    As of this writing, it cannot be applied in Inter-domain multicast or
    for Embedded-RP.  XXX: explain why not, someone send text? (one
    paragraph please!).

[...]
2.5.3  Bi-directional PIM

    Bi-directional PIM (see Section 2.1.3) was designed with faster
    multicast convergence in mind, and if fast failover is required, it
    may seem like an attractive solution.

    XXX: someone want to send a bit more text about the convergence
    differences wrt PIM-SM?

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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---

From: Dino Farinacci <[email-masked]>
Date: Sat, 30 Apr 2005 00:24:40 -0700

>> within a network", but maybe I misunderstood or this would not have 

    I can guess he is coming from the point of view that since there is
    less total state, all state can converge faster than in ASM and/or SSM.
    I was referring to the time it takes for a single route to converge.
    But having said that, when many (*,G) entries point to the same RP and
    that RP converges, then all routes converge at the same time.

    That should be clarified in the text you provided.

>> suggestions as how to reword them!

    Fine. But blanket statements can be misleading. A few more words like
    "total convergence" or "less state translate to better convergence" would
    be a good idea IMO.

Dino