OPS-DIR Review of draft-ietf-idr-cpr

[suehares]

OPS-DIR Review of -02

Location: https://datatracker.ietf.org/doc/review-ietf-idr-cpr-02-opsdir-early-romascanu-2024-05-31/

Dan's comment: Operational Considerations are described in Section 4. I found two places where clarifications are needed:

OPS-DIR-01, Section 4, paragraph 1

Text:

The CPR mechanism can be used in network scenarios where multiple inter-connected network domains belong to the same operator, or there is an operational trust model between the network domains of different operators. As described in section 5 of [I-D.hr-spring-intentaware-routing-using-color], the inter-domain intent-aware routing may be achieved with SR Policy across multiple domains, and services with specific intent can be steered to SR Policy at the ingress domain based on Color. While an operator may prefer a BGP-based solution for the reasons described there. Another possible consideration of the operator is the availability of inter- domain controller for end-to-end path computation.

Dan's comment 1

1. The first paragraph is unclear to me.

What does the sentence 'While an operator may prefer a BGP-based solution for the reasons described there.' mean? I guess that this is related to the previous statement

(' ... the inter-domain intent-aware routing may be achieved with SR Policy across multiple domains, and services with specific intent can be steered to SR Policy at the ingress domain based on Color')

with the intention of defining an exception, but the grammatical inconsistency makes the statement vague. Clarification is needed.

OPS-DIR-02, paragraph 03

The following paragraph reads:

There may be multiple inter-domain links between network domains,. A border node may receive CPR routes from multiple peering border nodes. Then the border node may take the attributes of the inter- domain links and/or the attributes of the received CPR routes into consideration to select the best path for specific Colored Prefixes to better meet the intent. The detailed mechanism is up to the operator's policy.

The first sentence seems incomplete. Moreover, what if the network domains belong to different operators with different policies? Operator's policies need to be somehow synchronized. How?

[suehares]

OPS-DIR-01, Section 4, paragraph 1

Status: Editorial, Technical clarity

Text:

The CPR mechanism can be used in network scenarios where multiple inter-connected network domains belong to the same operator, or there is an operational trust model between the network domains of different operators. As described in section 5 of [I-D.hr-spring-intentaware-routing-using-color], the inter-domain intent-aware routing may be achieved with SR Policy across multiple domains, and services with specific intent can be steered to SR Policy at the ingress domain based on Color. While an operator may prefer a BGP-based solution for the reasons described there. Another possible consideration of the operator is the availability of inter- domain controller for end-to-end path computation.

Dan's comment 1

1. The first paragraph is unclear to me.

What does the sentence 'While an operator may prefer a BGP-based solution for the reasons described there.' mean? I guess that this is related to the previous statement

(' ... the inter-domain intent-aware routing may be achieved with SR Policy across multiple domains, and services with specific intent can be steered to SR Policy at the ingress domain based on Color')

with the intention of defining an exception, but the grammatical inconsistency makes the statement vague. Clarification is needed.

Jie Dong's response:

https://mailarchive.ietf.org/arch/msg/ops-dir/bFfyt2invPOPEagYDjJCCm2Hpkg/

Sorry for the confusion caused by this text. Actually "the reasons described there" means the reasons described in [I-D.hr-spring-intentaware-routing-using-color], which is referred to in the first half of this sentence.

We can break this into shorter sentences to make this clearer.

Shepherd:

https://mailarchive.ietf.org/arch/msg/idr/B1orKjSxHN_U6uNkK1Z6ZHXKxMc/

Shepherd's suggested New text: / As described in section 5 of [I-D.hr-spring-intentaware-routing-using-color], the inter-domain intent-aware routing may be achieved by creating a logical tunnel defined by a SR Policy across multiple domains, and steering traffic for services with specific intent (signaled by Color) into the ingress of the tunnel. The logical inter-domain tunnel defined by an SR Policy may be established by BGP with the intent being signaled by Color Extended Community (Color-EC) or Color in the Tunnel Encaps Attribute (TEA-ColorTLV). This document proposes an alternate solution to signal intent by utilizing specific methods of assigning as the sub-locators of the node's base SRv6 locator. /

Dan's comment on shepherd's suggestions:

https://mailarchive.ietf.org/arch/msg/idr/kxoZlXPk9TKosIJgcpl-zKYhKmQ/

[suehares]

OPS-DIR-02, paragraph 03

The following paragraph reads:

There may be multiple inter-domain links between network domains,. A border node may receive CPR routes from multiple peering border nodes. Then the border node may take the attributes of the inter- domain links and/or the attributes of the received CPR routes into consideration to select the best path for specific Colored Prefixes to better meet the intent. The detailed mechanism is up to the operator's policy.

The first sentence seems incomplete. Moreover, what if the network domains belong to different operators with different policies? Operator's policies need to be somehow synchronized. How?

Jie's response:

https://mailarchive.ietf.org/arch/msg/idr/4MF-jvGDJkYk7cIYkRhxRbE6tBk/

Thanks for catching this nit. Either the comma in the first sentence should be removed, or the period is removed and an "and” is added to the beginning of the next sentence.

The operator's policy here refers to the mechanism used to select the best path from multiple received CPR routes. Yes the policy used in different domains needs to be consistent. Some coordination between the domains is needed, this is similar to the coordination of the color-mapping policy. We can add some text to make it clear.

Shepherd's comment: https://mailarchive.ietf.org/arch/msg/idr/B1orKjSxHN_U6uNkK1Z6ZHXKxMc/

Suggested new text:/ There may be multiple inter-domain links between network domains directly or via tunnels (SR Policy tunnels). A BGP speaker may receive CPR routes from multiple AS BGP speakers via EBGP. The local policy of a BGP speaker may take the attributes of the inter-domain links and the attributes of the received CPR routes into consideration when selecting the best path for specific Colored Prefixes to better meet the intent. The local policy of a BGP speaker is outside the scope of this document.

In a multiple-domain environment, the policy of BGP speakers in
multiple domains needs to be consistent. /

Dan's comments on Shepherd's suggestions

https://mailarchive.ietf.org/arch/msg/idr/kxoZlXPk9TKosIJgcpl-zKYhKmQ/

[suehares]

-02.txt status: Resolution for OPS-DIR-01 and OPS-DIR-02 approved, but required -03 version of draft