[c-nsp] MPLS and links with limited MTU size

Adam Vitkovsky Adam.Vitkovsky at gamma.co.uk
Mon Jan 25 06:46:47 EST 2016

Hey Saku,

> Saku Ytti [mailto:saku at ytti.fi]
> Sent: Monday, January 25, 2016 10:09 AM
> On 25 January 2016 at 11:23, Adam Vitkovsky
> <Adam.Vitkovsky at gamma.co.uk> wrote:
> > Interesting I didn't know that, do you know if LU or MQ is responsible for
> the fragmentation? But I'm afraid it would overload the Trio ensemble pretty
> quickly.
> > Yeah, on ASR9K the "to be fragmented" traffic has to be punted to LC CPU
> and that is subject to LPTS rate-limiting.
> LU is doing that, more specifically reorder block is doing that, same block
> which guarantees order of packets when single flow exceeds PPE capacity. I
> think per flow fragmentation is shy of 2Mpps, but it'll scale further by adding
> flows. At $job-1 we wanted to move some mobile network related
> fragmentation out from software device into the edge network MX, I was
> very dubious about the idea, but tested anyhow, and was surprised to find
> out how fast it worked.
Thank you very much for the details.
The MX LU truly is a marvellous chip, it's way ahead of Cisco's NPUs (can't comment on the nPower NPUs in NCS6k), it's unfortunate though that LU is just the only thing that stands out.
The rest will catch up eventually the question is where will the completion be at by then.


        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
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