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

From: "徐小虎(义先)" <[email-masked]>
Date: Sun, 22 Jul 2018 10:54:43 +0800

Hi all,

I just watched the IDR meeting record at https://play.conf.meetecho.com/Playout/?session=IETF102-IDR-20180719-1810

I'm in favor of the AD's recommendation of finding a unified proposal rather than two different proposals doing almost the same thing. BGP-SPF is intended to be a link-state protocol built on the BGP base protocol and L3 liveness works fine for link-state protocols (eg., OSPF). Hence I'm curious about the reason why L2 liveness is a must for BGP-SPF.  In other word, what's special for BGP-SPF as a link-state protocol that makes it have such "nice constrained problem"?

By the way, provided that BGP-SPF did need L2 liveness which in turn is expected by some BGP-SPF guys to be generic and therefore be applicable to other scenarios beyond BGP, wouldn't IEEE be a better place to pursue such generic L2 liveness mechanism?

Best regards,
Xiaohu

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From: "Jakob Heitz (jheitz)" <[email-masked]>
Date: Sun, 22 Jul 2018 03:06:55 +0000

What do you really mean by L2 liveness?
L2 can be Ethernet, Token Ring, ATM, Frame Relay, PPP, SLIP, MTP2 and others that may be invented in the future.
Each one needs its own liveness protocol. You will need to do it separately in each L2 protocol.
Do you mean the answer to the question:
Can the nodes at each end of the link forward IP packets to each other and forward those packets to the correct interface where they need to go?

Regards,
Jakob.

From: Idr <[email-masked]> On Behalf Of ???(??)
Sent: Saturday, July 21, 2018 7:55 PM
To: [email-masked]; [email-masked]
Subject: [Idr] Why L2 liveness needed for BGP-SPF

Hi all,

Best regards,
Xiaohu

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From: "徐小虎(义先)" <[email-masked]>
Date: Sun, 22 Jul 2018 11:16:24 +0800

Please look at the IDR meeting record starting from 00:48:00 (https://play.conf.meetecho.com/Playout/?session=IETF102-IDR-20180719-1810)

Best regards.
Xiaohu

------------------------------------------------------------------
From:Jakob Heitz (jheitz) <[email-masked]>
Send Time:2018年7月22日(星期日) 11:06
To:徐小虎(义先) <[email-masked]>; [email-masked] <[email-masked]>; [email-masked] <[email-masked]>; Randy Bush <[email-masked]>
Subject:RE: [Idr] Why L2 liveness needed for BGP-SPF

Regards,
Jakob.

  

Best regards, 
Xiaohu

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From: Randy Bush <[email-masked]>
Date: Sun, 22 Jul 2018 04:34:37 -0700

> L2 can be Ethernet, Token Ring, ATM, Frame Relay, PPP, SLIP, MTP2 and
> others that may be invented in the future.

it could be tin cans and a string.  but out here in the internet, it's
ethernet.  there are tiny vestiges of sonet, which you seem to have
forgotten; but no one is gonna run bgp-spf over them.  it is a mono-
culture; ethernet won.

randy

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From: Victor Kuarsingh <[email-masked]>
Date: Sun, 22 Jul 2018 10:09:12 -0400

At this point, the current applicability for BGP-SPF is Data Center / CLOS
networks as described in the applicability document (
https://tools.ietf.org/html/draft-keyupate-lsvr-applicability-02)

There is some texts around future use of this protocol (SP backbone), but
again not the focus of our current work.

That said, as noted by Randy, these topologies are currently Ethernet (at
least in the cases we are aware of).

Regards,

Victor K

> randy
>
> _______________________________________________
> Idr mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/idr
>

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From: Greg Mirsky <[email-masked]>
Date: Sun, 22 Jul 2018 09:43:44 -0500

Dear All,
hope an easy question you'll help me with. Liveness as path continuity
check or as connectivity verification.

Regards,
Greg

On Sun, Jul 22, 2018, 09:09 Victor Kuarsingh <[email-masked]> wrote:

> Lsvr mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/lsvr
>

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From: Robert Raszuk <[email-masked]>
Date: Sun, 22 Jul 2018 16:55:35 +0200

Is IETF a new forum for Ethernet specification ? I was always under slight
impression that this is rather IEEE Ethernet WG ...

http://www.ieee802.org/3/

On Sun, Jul 22, 2018 at 4:43 PM, Greg Mirsky <[email-masked]> wrote:

>> At this point, the current applicability for BGP-SPF is Data Center /
>> CLOS networks as described in the applicability document (

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From: Randy Bush <[email-masked]>
Date: Sun, 22 Jul 2018 08:42:26 -0700

> check or as connectivity verification.

layer 2 link liveness.  we have other tools above layer 2; e.g. bfd.

randy

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From: Greg Mirsky <[email-masked]>
Date: Sun, 22 Jul 2018 12:16:20 -0500

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

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From: Robert Raszuk <[email-masked]>
Date: Mon, 23 Jul 2018 00:49:00 +0200

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.

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From: Greg Mirsky <[email-masked]>
Date: Sun, 22 Jul 2018 15:55:56 -0700

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 <[email-masked]> wrote:

> Just to note L3 BGP Hellos to discover topology is terrible idea even
> worse then LLDP one.
>
> Thx,
> R.
>
>