Hi Ron, From: Ron Bonica <rbonica=40juniper....@dmarc.ietf.org> Date: Tuesday, August 17, 2021 at 2:20 PM To: Acee Lindem <a...@cisco.com>, "lsr@ietf.org" <lsr@ietf.org> Subject: RE: [Lsr] RFC 8919, RFC 8920, Flex Algo, and Flex Algo BW Constraints
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 I’m having trouble envisioning this whole solution where bandwidth for Flex Algo constraints is configured centrally. But in any case, the Robert indicated how one could advertise an ASLA for all applications. Thanks, Acee Ron Juniper Business Use Only From: Acee Lindem (acee) <acee=40cisco....@dmarc.ietf.org> Sent: Friday, August 13, 2021 10:22 AM To: Ron Bonica <rbon...@juniper.net>; lsr@ietf.org 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 <lsr-boun...@ietf.org<mailto:lsr-boun...@ietf.org>> on behalf of Ron Bonica <rbonica=40juniper....@dmarc.ietf.org<mailto:rbonica=40juniper....@dmarc.ietf.org>> Date: Thursday, August 12, 2021 at 3:46 PM To: "Acee Lindem (acee)" <acee=40cisco....@dmarc.ietf.org<mailto:acee=40cisco....@dmarc.ietf.org>>, "lsr@ietf.org<mailto:lsr@ietf.org>" <lsr@ietf.org<mailto:lsr@ietf.org>> 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 <lsr-boun...@ietf.org<mailto:lsr-boun...@ietf.org>> On Behalf Of Acee Lindem (acee) Sent: Tuesday, August 10, 2021 4:43 PM To: lsr@ietf.org<mailto:lsr@ietf.org> 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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