Acee,
So, let us discuss whether there is a good reason for
draft-ietf-lsr-flex-algo-con to specify ASLA !
Link attributes are different from application configuration information. Link
attributes are properties of a link. They are independent of the applications
that use them. The following are examples:
* Total physical bandwidth
* Number of LAG elements
* Bandwidth of smallest lag member
* Latency
Link attributes do not benefit from ASLA encoding because they are not
application specific.
Application configuration information constrains the behavior of an
application. It can apply to:
* The application and a link
* The application only
Bandwidth reservation applies to an application and a link. For example, a link
may advertise that it has:
* X Gbps available for RSVP-TE reservations
* Y Gbps available for SR Policy reservations
* Z Gbps available for TI-LFA reservations
This class of configuration information clearly benefits from ASLA encoding,
because it is applicable to both the application and the link.
Some applications (e.g., Flexalgo) can be configured to use a variety of link
attributes in SPF calculation. No matter how they acquire this configuration
information, it MUST be the same at each node. Otherwise, routing loops may
result. Configuration options are:
1. Configure this information on each link and advertise link attributes
with ASLA
2. Configure this information on each node that runs the application
3. Configure this information in a few central places and advertise it to
all other nodes. The advertisement is not associated with a link. Flexalgo uses
the FAD in this manner.
Neither Option 1 nor Option 2 is very appealing, because it requires
configuration on each node. Option 3 is better because:
* It requires configuration on only a few nodes
* It maintains separation between link attributes and application
configuration information
* It can support applications like Flexalgo, where each algorithm may use
different link attributes to calculate the shortest path
Ron
Juniper Business Use Only
From: Acee Lindem (acee) <[email protected]>
Sent: Friday, August 13, 2021 10:22 AM
To: Ron Bonica <[email protected]>; [email protected]
Subject: Re: [Lsr] RFC 8919, RFC 8920, Flex Algo, and Flex Algo BW Constraints
[External Email. Be cautious of content]
Speaking as a WG member:
Hi Ron,
My rationale is #1. The LSR WG developed ASLAs to cover usage of the link
attributes (including metrics) for different applications and mitigate all the
vagaries of the original TE link attribute specifications. ASLAs are
implemented and deployed. I believe it would be a mistake to bifurcate the IGP
standards with yet another way of encoding link attributes for different
applications.
Thanks,
Acee
From: Lsr <[email protected]<mailto:[email protected]>> on behalf of Ron
Bonica
<[email protected]<mailto:[email protected]>>
Date: Thursday, August 12, 2021 at 3:46 PM
To: "Acee Lindem (acee)"
<[email protected]<mailto:[email protected]>>,
"[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>>
Subject: Re: [Lsr] RFC 8919, RFC 8920, Flex Algo, and Flex Algo BW Constraints
Acee,
Please help me to parse your message. It is clear that you want
draft-ietf-lsr-flex-algo-bw-con to specify ASLA's. However, your rationale is
not so clear.
It is not because RFC 8919 mandates ASLA. In fact, we agree that it would be
strange for an RFC to include a mandate that precludes future proposals.
Are any of the following your rationale:
1) Because there is a good technical reason for
draft-ietf-lsr-flex-algo-bw-con to specify ASLA
2) Because it is possible, but not necessary, for
draft-ietf-lsr-flex-algo-bw-con to specify ASLA
3) Because it was the unstated intention of RFC 8919 to include a mandate
that precludes future proposals (although we agree that this would be strange).
For the purposes of full disclosure, I think discussion regarding the first
rationale would be fruitful. However, I don't think very much of the second or
third rationale.
Ron
Juniper Business Use Only
From: Lsr <[email protected]<mailto:[email protected]>> On Behalf Of Acee
Lindem (acee)
Sent: Tuesday, August 10, 2021 4:43 PM
To: [email protected]<mailto:[email protected]>
Subject: [Lsr] RFC 8919, RFC 8920, Flex Algo, and Flex Algo BW Constraints
[External Email. Be cautious of content]
Speaking as a WG Member:
In reviewing RFC 8919 and RFC 8920, it is clear that the ASLA mechanism was
to be used for new link attributes and applications. While the documents do not
mandate that there never could be a new way to advertise link attributes, this
was clearly the intent. Indeed, it would be strange for an RFC to include a
mandate that precluded future proposals. The advertisement enablement and
deployment sections of these documents specifically cover future attributes and
applications.
Given that we have ASLAs as building blocks, I don't really see a reason to
introduce the generic metric. The proponents say it isn't an alternative to
ASLAs but their examples cite different applications using different metric
types (i.e., application-specific metrics). Also, given that ASLA are used by
the base Flex Algo draft, it would be inconsistent to diverge for Flex Algo BW
constraints.
Consequently, I would request that draft-ietf-lsr-flex-algo-bw-con-01 revert
to using ASLAs. Based on the LSR Email discussion prior to IETF 111, this was
definitely the consensus.
Thanks,
Acee
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