Arista Routing Solutions

lincoln dale ltd at
Sun Apr 24 23:47:07 UTC 2016

> > High Touch / Low Touch
> High touch means very general purpose NPU, with off-chip memory. Low
> touch means usually ASIC or otherwise simplified pipeline and on-chip
> memory. Granted Jericho can support off-chip memory too.
> L3 switches are canonical example of low touch. EZchip, Trio, Solar,
> FP3 etc are examples of canonical high touch NPUs. What low touch can
> do, it can do fast and economically.

Your analogy makes some sense, but what you classify as high-touch /
low-touch is just one dimension and could do with a more modern update.

I'd suggest a more modern analogy would be that historically the difference
between a L3 switch and a router is the former has a fixed processing
pipeline, limited buffering (most are just on-chip buffer) and limited
table sizes.
But more modern packet processors with fixed pipelines often have blocks or
sections that are programmable or flexible. e.g. with a flexible packet
parser, its possible to support new overlay or tunnel mechanisms, flexible
key generation makes it possible to reuse different table resources in
different ways, flexible rewrite engine means egress encap or tunnels or
logic can be done.
There's also often more capacity for recirc or additional stages as

Specific to Jericho, the underlying silicon has all these characteristics.
We [*] used the flexibility in all of the stages both now and in previous
iterations (Arad) to add new features/functionality that wasn't natively
there to start with. And it uses a combination of on-chip & off-chip
buffering with VoQ

Its also not only Arista that call it a router cisco do too (NCS5K5).

Sure, using a NPU for packet processing essentially provided a 100%
programmable packet forwarding pipeline, and maybe even a "run to
completion" kind of packet pipeline where the pipeline could have a long
tail of processing. However, engineering is a zero sum game, and to do that
means you sacrifice power or density, or most often, both.

I agree the lines have been blurred as to the characteristics, and we'd
openly state that its not going to be useful in every use case of where a
router is deployed, but for specific use cases, it fits the bill and has
compelling density, performance and cost dynamics.

To the OPs question, there are people running with this in EFT and others
in production.
My suggestion would be that if you think its of interest, reach out to your
friendly Arista person [*] and try it out or talk through what it is you're
after. We are generally a friendly bunch and often we can be quite creative
in enabling things in different ways to old.

> Yeah they are certainly much behind in features, but if you don't
> need those features, it's probably actually an advantage. For my
> use-cases Arista's MPLS stack is not there.

We've historically had the data-plane but not the control-plane. Thats a
work in progress.
Again, often there are creative solutions to ways of doing things that
aren't necessarily the same as old ways but achieve the same end result.


[*] disclosure: i work on said products described ltd at

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