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Nexus 5K QoS questions

Hello,

I have been reading through the 5K config guides and going over some Cisco Live 365 documentation in order to better understand queuing on the 5K platform, and I have a few things that require clarification.  I have included a couple drawings that will better illustrate my questions (in red), but at a high level here is what I need help understanding:

1) Where do the input and output queuing policies take effect?  The config guide suggests that an input queuing policy is only used to tell a CNA about its policy through DCBX.  But some of the CiscoLive365 presentations seem to suggest otherwise (see drawing, which is a snippet from the 5K Architecture Breakout, BRKARC-3452).  Also, where specifically do the output queuing policies take effect?  Because everything is ingress buffered and subsequently scheduled off of the VoQs, it would make sense if the egress interface's queuing policy tells the scheduler how to behave.  Is that right?  Because my understanding is that the actual egress queues only get used in very rare instances when a PAUSE is received while a packet is in transit on the fabric.

2) Why are the QoS groups required?  I suspect that they are needed because of the lack of hardware queues, so they effectively map a class of traffic into a VoQ.  Is that correct?

5K Queuing questions.png

Questions from N5K Arch breakout.png  

Thanks,

Brett

  • Server Networking
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