Re: [Lsr] Comments on Requested Codepoints for draft-li-lsr-isis-area-proxy

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Mon, 29 June 2020 21:13 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: "tony.li@tony.li" <tony.li@tony.li>, Hannes Gredler <hannes@gredler.at>
CC: "draft-li-lsr-isis-area-proxy.authors@ietf.org" <draft-li-lsr-isis-area-proxy.authors@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
Thread-Topic: [Lsr] Comments on Requested Codepoints for draft-li-lsr-isis-area-proxy
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Subject: Re: [Lsr] Comments on Requested Codepoints for draft-li-lsr-isis-area-proxy
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Tony –

OLD:
1)Area Proxy Router Capability - sub-TLV of Router Capability TLV

2)Inside Node TLV - Top level TLV

3)Area Proxy TLV - Top Level TLV with optional sub-TLVs:
   Sub-TLV Area Proxy System ID
   Sub-TLV Area Segment SID

4)Area Segment SID - Top Level TLV

NEW: (Please check my interpretation)

1)Area Proxy Router Capability - sub-TLV of Router Capability TLV

2)Area Proxy TLV - Top Level TLV with optional sub-TLVs:
   Sub-TLV Area Proxy System ID
   Sub-TLV Area Segment SID
   Sub-TLV Inside Node ???

3)Area Segment SID - Top Level TLV

Am I correct so far??

If so, a couple more comments/suggestions:

a)Could the Area Proxy TLV become a bit more generic and allow advertisement of the capability (implied by presence of the TLV)?
If  so, the Router Capability sub-TLV could go away.

b)If the Area Segment SID is (as you suggest) a generic thing not specific to Area Proxy, then I would point you to https://www.rfc-editor.org/rfc/rfc8667.html#section-2.4.1
This allows SIDs to be advertised in the SID Binding TLV for a special purpose (see the Mirror SID). One could imagine another flag bit to indicate this is an Area SID.
I think this would need to be vetted with SR  folks – but I would like to avoid advertising a SID in a way different from all other SIDs i.e., SIDs currently are always a sub-TLV of some top level TLV – whether it be Prefix Reachability (Prefix-SID), IS Neighbor (Adjacency SID), or Binding SID (Mirror SID).

   Les


From: Tony Li <tony1athome@gmail.com> On Behalf Of tony.li@tony.li
Sent: Monday, June 29, 2020 12:52 PM
To: Hannes Gredler <hannes@gredler.at>
Cc: Les Ginsberg (ginsberg) <ginsberg@cisco.com>om>; draft-li-lsr-isis-area-proxy.authors@ietf.org; lsr@ietf.org
Subject: Re: [Lsr] Comments on Requested Codepoints for draft-li-lsr-isis-area-proxy



Hi,

The authors have conferred and we would like to propose the following changes:

- The semantics of the Inside Node TLV will be folded into the Area Proxy TLV.

- The Area Proxy TLV will have its scope expanded to include pseudonodes.

- No change to the Area Segment SID TLV encoding.

Comments?   Especially from our Designated Experts?

Regards,
Sarah, Vivek, Gyan, and Tony



On Jun 25, 2020, at 12:04 PM, tony.li@tony.li<mailto:tony.li@tony.li> wrote:


Hi Hannes,

Thanks for your comments.  We will propose an alternate encoding.

Tony



On Jun 25, 2020, at 10:47 AM, Hannes Gredler <hannes@gredler.at<mailto:hannes@gredler.at>> wrote:

Hi Tony,

I do share Les’ concerns on burning top-level 8-bit code point space at this point.

At this point it is not me to judge wether CAP TLV or GENAPP TLV or something else should be a more appropriate place.
Please let's have a WG discussion on this.

Thanks,

/hannes


On 21.06.2020, at 18:50, tony.li@tony.li<mailto:tony.li@tony.li> wrote:


Les,

We don’t have to resolve this now.
One of my motivations for sending this was related to Early Allocation of code points. Since you have already asked once, I am assuming that if WG adoption is achieved it will be swiftly followed by an early allocation request – and as one of the Designated Experts I wanted to share my concerns sooner rather than later.


I appreciate that.  Do others share Les’ perspective on the relative tradeoffs?  Especially our other Desginated Experts?


Would this argue for advertising “this is a boundary circuit” in pseudo-node LSPs for boundary circuits rather than advertising “inside” on all inside pseudo-nodes?

You could do it that way.  It inverts the semantics and inverts the deployment.  Logically, it should have the same effect.  However, it then is seen by outside nodes.  Since they need not support Area Proxy, this seemed like a riskier approach, thus we opted for marking inside pseudonodes.

[Les:] My point was largely motivated by the statement in the draft:

“Area Proxy Boundary multi-access circuits (i.e.  Ethernets in LAN
   mode) with multiple Inside Edge Routers on them are not supported.”

So it seems advantageous to be able to prevent this from happening – which requires some signaling on the circuit in question.



I think that the case that you’re concerned about is already easily detected.  Recall that an Inside Edge router will generate IIH’s onto a boundary circuit using the Proxy system ID.  Thus, if an Inside Edge router receives an IIH with a source address of it’s own proxy system id, then it has encountered this issue.

Tony


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