Elwyn,
On 18/05/2020 23:02, elwynd wrote:
Hi.
I am not convinced by the discussion that has ensued from my review.
s3, para 3:
If the router supports ELs on all of its interfaces, it SHOULD
advertise the ELC with every local host prefix it advertises in OSPF.
- Both Acee amd I didn't immediately understand that 'every local host prefix' was not every
prefix that the router might advertise. It would be good to explain that this is the case.
what exactly needs to be explained? The local property of the prefix?
- As I previously stated, with a SHOULD it ought to be explained why one might not want to
advertise the ELC with some subset of the local host prefixes.
SHOUDL is used not to say that one does it for subset of host prefixes,
but rather because MUST can not be used for reasons mentioned earlier.
From the functionality perspective it is sufficient to advertise it
with a single local prefix. We specified for "every local prefix" to
make it simpler.
- Given that there are now two sets of prefixes, would/SHOULD/MUST ELC be advertised with the
prefixes that are not local host prefixes?
no, only with local host prefixes. I can add "MUST NOT be advertised
with any other prefix" if that's what you are after.
s4, para 3:
The absence of ERLD-MSD advertisements indicates only that the
advertising node does not support advertisement of this capability.
Firstly, I cannot see why this statement or its absence might affect other EL mechanisms that
don't use OSPF to do signaling of ELC.
It does not. All we say that if it is not advertised by OSPF, it means
the router does not support the advertisement in OSPF. Nothing else. It
has no effect on any other mechanisms that might be used to derive these
capabilities.
If I understand RFC 8662 correctly, if OSPF is being used to distribute ELC adverts and the ERLD
is not advertised by OSPF, then either the ERLD has to be supplied by other means or it will
effectively default to zero.
Thus, I would suggest that the paragraph above should be replaced with:
Advertisement of ERLD via OSPF using ERLD-MSD is OPTIONAL. If a router does not advertise
ERLD, then the EL positioning calculations described in [RFC8662] will assume a vaue of zero
for the ERLD of this router unless a different value is supplied by alternative means.
I don't think we should be specifying anything that belongs to RFC8662
here in this draft. What we specify in this draft is how to advertise
something in OSPF, not how this is being used, because this information
is not used by OSPF. The usage of this info is outside of the scope of
this draft and if anything needs to be added in that regard it should be
done by updating the RFC8662.
regards,
Peter
Regards,
Elwyn
Sent from Samsung tablet.
-------- Original message --------
From: "Acee Lindem (acee)" <acee@xxxxxxxxx>
Date: 14/05/2020 21:43 (GMT+00:00)
To: Alvaro Retana <aretana.ietf@xxxxxxxxx>, "Peter Psenak (ppsenak)"
<ppsenak@xxxxxxxxx>, Elwyn Davies <elwynd@xxxxxxxxxxxxxx>, gen-art@xxxxxxxx
Cc: last-call@xxxxxxxx, draft-ietf-ospf-mpls-elc.all@xxxxxxxx, lsr@xxxxxxxx
Subject: Re: Genart last call review of draft-ietf-ospf-mpls-elc-13
Hi Alvaro, Elwyn,
*From: *Alvaro Retana <aretana.ietf@xxxxxxxxx>
*Date: *Thursday, May 14, 2020 at 3:46 PM
*To: *Acee Lindem <acee@xxxxxxxxx>, "Peter Psenak (ppsenak)"
<ppsenak@xxxxxxxxx>, Elwyn Davies <elwynd@xxxxxxxxxxxxxx>,
"gen-art@xxxxxxxx" <gen-art@xxxxxxxx>
*Cc: *"last-call@xxxxxxxx" <last-call@xxxxxxxx>,
"draft-ietf-ospf-mpls-elc.all@xxxxxxxx"
<draft-ietf-ospf-mpls-elc.all@xxxxxxxx>, "lsr@xxxxxxxx" <lsr@xxxxxxxx>
*Subject: *Re: 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?
That’s true – but not advertising the OSPF capability could imply that
either ELC MSD or advertisement of the OSPF capability is not supported.
Although I might not have worded it as such, that was clear to me from
the text. Feel free to recommend alternate text if you feel it is
necessary.
Thanks,
Acee
Thanks!
Alvaro.
On May 11, 2020 at 3:18:34 PM, Acee Lindem (acee) (acee@xxxxxxxxx
<mailto:acee@xxxxxxxxx>) 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?
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