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

Christian Hopps <chopps@chopps.org> Thu, 25 June 2020 00:17 UTC

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From: Christian Hopps <chopps@chopps.org>
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Date: Wed, 24 Jun 2020 20:17:49 -0400
Cc: Christian Hopps <chopps@chopps.org>, Les Ginsberg <ginsberg@cisco.com>, "draft-li-lsr-isis-area-proxy.authors@ietf.org" <draft-li-lsr-isis-area-proxy.authors@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
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Subject: Re: [Lsr] Comments on Requested Codepoints for draft-li-lsr-isis-area-proxy
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> On Jun 21, 2020, at 12:50 PM, 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?

[Designated Expert hat]

I agree that we should try and reduce the number of top-level TLV allocations being made here.

[WG member hat]

I think using router capabilities to eliminate the Area Proxy TLV is one choice, and you shouldn't be afraid of storing some capability related extra octets in it, plenty of other users do this already.

However, if you're still going to need a top-level TLV for "Inside Node" (perhaps b/c we fear using a Router Capability TLVs in pseudo-node?), then why not create a single top level "Area Proxy TLV" for all Area Proxy uses (i.e., make the current "Area Proxy TLV" and "Inside Node TLV" sub-TLVs of that top-level container) instead?

Thanks,
Chris.
[see above for hats]

> 
> 
>> 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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