Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-shared-ring-protection-05
Huub van Helvoort <huubatwork@gmail.com> Sun, 12 July 2015 11:00 UTC
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Date: Sun, 12 Jul 2015 13:00:34 +0200
From: Huub van Helvoort <huubatwork@gmail.com>
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To: Yimin Shen <yshen@juniper.net>, "draft-cheng-mpls-tp-shared-ring-protection@tools.ietf.org" <draft-cheng-mpls-tp-shared-ring-protection@tools.ietf.org>
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Subject: Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-shared-ring-protection-05
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Thank you for your review.
Here is our response: in-line [Huub] on behalf of the authors.
Best regards. Huub.
======
On 10-07-15 03:37, Yimin Shen wrote:
[Huub] Multiple failures means that more than one link or node in the ring can fail. Protection can still be performedDear authors, chairs, and WGI’ve been asked by the WG chairs to review draft-cheng-mpls-tp-shared-ring-protection-05 for WG adoption. Overall, I think the draft is trying to address a valid MPLS-TP scenario by using a promising solution. However, I have the following comments and questions for sections 1 to 4, which I would like to request the authors to answer and clarify.
- Section 2.1 – Recovery of multiple failures
- This is misleading to me. The draft seems to only be able to handle a single failure per ring, rather than multiple failures per ring. This may need some clarification.
in the "islands" created in this way. A node failure is in fact the same as adjacent link failures.
We can provide more clarification.
[Huub] OK.
- I’d like to suggest to change term “exit node” to “egress node”.
[Huub] clarifying text can be added. We can add a section describing provisioning the ring-nodes.
- Section 4.1 - The ring tunnel layer.
- Given a ring of N nodes, this layer would consist of 4xN ring tunnels. The draft is a little light on the provisioning and management aspects of this layer, while pushing a lot of complexity to this layer.
[Huub] each node knows this because of the ring-map which contains this information.
- Each node is traversed by many tunnels. How does it know whether a tunnel is working or protecting, and whether a tunnel is CW or AW ? How does it associate a working tunnel with a protecting tunnel (to the same egress node, but opposite in direction) ?
[Huub] from the ring-map the ingress node knows what the shortest path is and then decides to take the CW or the AW tunnel.
- When an ingress node needs a working tunnel to a particular egress node, how does choose between the CW tunnel and the AW tunnel, especially when one is significantly longer (i.e. of higher cost) than the other ?
[Huub] mixing working and protecting traffic in a single tunnel would make the RPS protocol more complex.
- The draft describes 4 tunnels (CW, AW, CP, AP) per egress node ? Is it possible to use only 2 tunnels (i.e. CW and AW) and have them protect each other ?
An egress node cannot make the distinction.
[Huub] No it doesn't, section 4.3.1 explains wrapping for link failure and node failure.
- Section 4.3.2 -- Short wrapping vs. “traditional wrapping”
- Does “traditional wrapping” refer to the scenario in section 4.3.1 ?
[Huub] the description of traditional wrapping is in the first paragraph of section 4.3.2, more clarification can be added.
[Huub] 4.3.1 explains wrapping methodology, its application is described in 4.3.2.
- The 4.3.2 mode seems superior to the 4.3.1 mode in all aspects. If so, would there be any value to keep 4.3.1 mode.
[Huub] No, not correct. During a protection switch CW tunnel ==> AP tunnel and AW tunnel ==> CP tunnel.
- In 4.3.2 mode, CW tunnel ==CP tunnel and AW tunnel == AP tunnel in path topology, correct ? If so, you could reduce the number of tunnels per egress node from 4 to 2 (as comment [4] above), correct ?
[Huub] to operate properly ring protection switching has to be revertive, after repair the traffic should be switched back to working (shortest path)
- Section 4.3.3
- This is equivalent to “global repair” in MPLS. However, why does the ingress node switch traffic from CW tunnel to AP tunnel instead of AW tunnel ? A working tunnel should be “better” than a protecting tunnel to permanently carry traffic.
[Huub] the ring-map has to take care of this.
- Section 4.4
- I’m not sure how label swap would work on an interconnection node, as the draft describes it. In Fig-12, in normal state, F receives a packet from ring-1; The top label X is a tunnel to the node group; The next label Y is the service LSP. So, F pops label X, and “ the label used for working ring tunnel R2cW_I will be pushed based on the inner label” (i.e. label Y). How could F have the knowledge about the service LSP, its label Y, and its egress node, etc ?
- I may have more questions to follow after the above…
Regards,Yimin ShenJuniper Networks
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- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Yimin Shen
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Gregory Mirsky
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Huub van Helvoort
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Huub van Helvoort
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Yimin Shen
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Yimin Shen
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… Dongjie (Jimmy)
- Re: [mpls] MPLS-RT review of draft-cheng-mpls-tp-… weiqiang cheng