Re: [Lsr] Genart last call review of draft-ietf-ospf-mpls-elc-13

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Thu, 14 May 2020 21:46 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: Alvaro Retana <aretana.ietf@gmail.com>, "Acee Lindem (acee)" <acee@cisco.com>, "Peter Psenak (ppsenak)" <ppsenak@cisco.com>, Elwyn Davies <elwynd@dial.pipex.com>, "gen-art@ietf.org" <gen-art@ietf.org>
CC: "lsr@ietf.org" <lsr@ietf.org>, "last-call@ietf.org" <last-call@ietf.org>, "draft-ietf-ospf-mpls-elc.all@ietf.org" <draft-ietf-ospf-mpls-elc.all@ietf.org>
Thread-Topic: [Lsr] Genart last call review of draft-ietf-ospf-mpls-elc-13
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Date: Thu, 14 May 2020 21:46:10 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/lsr/o_YTOPbhcZiIZKnP8ID_5e_scmw>
Subject: Re: [Lsr] Genart last call review of draft-ietf-ospf-mpls-elc-13
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Elwyn’s comment was:

<snip>
I was trying to understand
why a router that satisfies the previous condition so that it is
legitimate for it to announce ELC with any IP address prefix might wish
to only announce it with some prefixes and not others.
<end snip>

The answer to that is clearly stated in the draft (emphasis added):

“If the router supports ELs on all of its interfaces, it SHOULD
   advertise the ELC with every local host prefix it advertises in OSPF.”


What is needed is to know whether traffic routed via a particular node can depend upon that node supporting EL.  That info is communicated by advertising ELC for the local host prefixes only.
No need to do so for other prefixes.

HTH

   Les


From: Lsr <lsr-bounces@ietf.org> On Behalf Of Alvaro Retana
Sent: Thursday, May 14, 2020 12:46 PM
To: Acee Lindem (acee) <acee@cisco.com>om>; Peter Psenak (ppsenak) <ppsenak@cisco.com>om>; Elwyn Davies <elwynd@dial.pipex.com>om>; gen-art@ietf.org
Cc: lsr@ietf.org; last-call@ietf.org; draft-ietf-ospf-mpls-elc.all@ietf.org
Subject: Re: [Lsr] Genart last call review of draft-ietf-ospf-mpls-elc-13

Hi!

Yes, we cannot specify something that routers unaware of this specification should or shouldn’t do.

I believe that Elwyn’s point is this: *if a router supports this specification* then when would it not advertise the ELC?  IOW, the specification only obviously applies to implementations that support it — in that case I would think that if a router supports ELs on all of its interfaces then it would always advertise the ELC, right?


Thanks!

Alvaro.


On May 11, 2020 at 3:18:34 PM, Acee Lindem (acee) (acee@cisco.com<mailto:acee@cisco.com>) wrote:
Note that the optionality of ERLD-MSD advertisements appears on
reflection to be a more serious issue than just an editorial nit.

So what would you suggest? There are existing implementations that support multipath forwarding entropy using MPLS entropy labels but do not signal that capability in OSPF. We can't have a document that retroactively mandates that they signal it. This wouldn't be backward compatible. How can you possibly see this as a serious issue?