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Re: [Idr] [Lsvr] Why L2 liveness needed for BGP-SPF

Greg Mirsky <gregimirsky@gmail.com> Sun, 22 July 2018 22:56 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Sun, 22 Jul 2018 15:55:56 -0700
Message-ID: <CA+RyBmVrYCDbWfLwDmnX6R4TnJnD7Tg7CU6jFEXkzQW5EQS9eQ@mail.gmail.com>
To: Robert Raszuk <robert@raszuk.net>
Cc: Randy Bush <randy@psg.com>, idr wg <idr@ietf.org>, "Lsvr@ietf.org" <Lsvr@ietf.org>
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Subject: Re: [Idr] [Lsvr] Why L2 liveness needed for BGP-SPF
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Hi Robert,
thank you for the clarification. I've got interested in the discussion
since "liveliness" often used as the alternative for "continuity check".
But if it's topology discovery with or without capability advertisement,
I'll sit down.

Regards,
Greg

On Sun, Jul 22, 2018 at 3:49 PM, Robert Raszuk <robert@raszuk.net> wrote:

> Hey Greg,
>
> I don't think this is about liveness or connectivity verification.
>
> It is all about physical topology discovery at L2 without one of two
> popular link state protocol which today do the job just fine. Whoever is
> asking for it is however correct that we don't have a protocol independent
> way of discovering Ethernet topologies. If it is a feature or a drawback
> remains to be seen.
>
> I was observing identical struggle in OF .. as expected it failed pretty
> badly !
>
> Just to note L3 BGP Hellos to discover topology is terrible idea even
> worse then LLDP one.
>
> Thx,
> R.
>
>
> On Sun, Jul 22, 2018 at 7:16 PM, Greg Mirsky <gregimirsky@gmail.com>
> wrote:
>
>> Hi Randy,
>> thank you for the quick response to my question. BFD monitors path
>> continuity at the layer 3, though there's BFD over LAG that picks into the
>> layer 2. One cannot differentiate between liveness of the remote system and
>> availability of the path between two systems. If we are not interested
>> whether packets from the particular source and only that source received,
>> then we use path continuity check protocol. BFD is the example of the CC
>> while CFM, Layer 2, is the connectivity verification.
>>
>> Regards,
>> Greg
>>
>> On Sun, Jul 22, 2018, 10:42 Randy Bush <randy@psg.com> wrote:
>>
>>> > hope an easy question you'll help me with. Liveness as path continuity
>>> > check or as connectivity verification.
>>>
>>> layer 2 link liveness.  we have other tools above layer 2; e.g. bfd.
>>>
>>> randy
>>>
>>
>> _______________________________________________
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>>
>

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