[Cerowrt-devel] trying to make sense of what switch vendors say wrt buffer bloat

[Eric Johansson <esj@eggo.org>]

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one of my clients asked arista about bufferbloat issues in their
switches.  here was their response.  is their analysis right?

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Buffer bloat was a relevant on 10/100M switches, not 10Gb switches. At
10Gb we can empty the queue in ~100ms, which is less than the TCP
retransmission timers, therefore no bloat. Buffer bloat can happen at
slower speeds, but not an issue at the speeds we have on our switches. 

There are some articles regarding bufferbloat on the net, but buffer
bloat is not a problem on our switches.  Some of the information
regarding bufferbloat sites Internet routers where packets can be held
in queues of very large buffers for several seconds, up to 10 seconds
which can cause TCP retransmission problems and lower overall
application performance when going across the public Internet.

The buffers on the Arista 7500 are 128MB of packet buffers per 10GbE
port coupled to a fully arbitrated (VOQ) virtual output queue forwarding
system.  At 10Gbps this is ~100msec of buffer capacity which is an order
of magnitude from ‘1 second’ and 2 orders of magnitude from the 10
seconds worst case identified in buffer bloat documents.

We (Arista) have switching systems with large buffers and high port
count, or low buffers and high port count running one operating system.
Buffer bloat is real in systems that would have more than 1.25GB of
packet buffer per 10Gb port - none of these systems contribute to the
buffer bloat issue.

We position deep buffering switches where lossless performance is
necessary.  


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