nanog mailing list archives
RE: [c-nsp] LDPv6 Census Check
From: <adamv0025 () netconsultings com>
Date: Mon, 15 Jun 2020 09:47:37 +0100
From: David Sinn Sent: Friday, June 12, 2020 4:19 PMOn Jun 11, 2020, at 2:02 PM, Mark Tinka <mark.tinka () seacom mu> wrote: On 11/Jun/20 17:32, David Sinn wrote:Respectfully, that is deployment dependent. In a traditional SP
topology
that focuses on large do everything boxes, where the topology is fairly
point-
to-point and you only have a small handful of nodes at a PoP, labels can
be
fast, cheap and easy. Given the lack of ECMP/WECMP, they remain fairly efficient within the hardware.However if you move away from large multi-chip systems, which hideinternal links which can only be debugged and monitored if you know the
the
obscure, often different ways in which they are partially exposed to the operator, and to a system of fixed form-factor, single chip systems,
labels fall
apart at scale with high ECMP.I'm curious about this statement - have you hit practical ECMP issues with label switching at scale?Yes. Path enumeration when you use mult-tier Clos topologies within a PoP causes you many, many problem.
Hi David, Can you be more specific please? Maybe some examples with numbers. I can see how you might run out of L2 rewrite/adjacency table space on a particular node if you enumerate every possible path downstream of it (especially on leaf nodes), cause that number is has a dependency on the size of the fabric in terms of the total number of links in the fabric (which balloons quickly). Let's focus on the alternate case then, (the deep label-stack one) At each node in the multi-tier Clos (which I assume is the Russ White's butterfly model? But any Clos or Benes fabric needs the same) you need to program a label to uniquely identify each egress interface ,so now there's this nice one-to-one relationship between label and egress interface. Now the depth of the label-stack depends on the number of hops the packet needs to traverse across the fabric. But how deep could the fabric realistically be? Even in the "butterfly" model with separate pods instead of leaf nodes I counted 9 hops (that's not ultra-deep is it)? It's the VM doing label imposition as programmed by the fabric controller (all in SW so can go as deep as you want) and all fabric nodes are just popping top label so no big deal. adam
Current thread:
- RE: [c-nsp] LDPv6 Census Check, (continued)
- RE: [c-nsp] LDPv6 Census Check adamv0025 (Jun 16)
- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 16)
- RE: [c-nsp] LDPv6 Census Check adamv0025 (Jun 16)
- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 17)
- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 15)
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- Re: [c-nsp] LDPv6 Census Check Christian Meutes (Jun 12)
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- Re: [c-nsp] LDPv6 Census Check Christian Meutes (Jun 14)
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- RE: [c-nsp] LDPv6 Census Check adamv0025 (Jun 11)
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- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 11)
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- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 12)
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- RE: [c-nsp] LDPv6 Census Check adamv0025 (Jun 15)
- Re: LDPv6 Census Check Saku Ytti (Jun 10)
- Re: LDPv6 Census Check Mark Tinka (Jun 10)
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- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 10)
- Re: LDPv6 Census Check Radu-Adrian Feurdean (Jun 11)
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- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 11)
- Re: [c-nsp] LDPv6 Census Check Nick Hilliard (Jun 11)
- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 11)
- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 10)
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- Re: [c-nsp] LDPv6 Census Check Mark Tinka (Jun 10)