I am a Systems Administrator at a small firm. We are latency sensitive. When forwarding packets, what protocols use the CPU and which use the ASICs?
We have mostly Arista 7124's (for the most latency sensitive bits) and Cisco 4948's. I imagine that the architecture for an Arista and a Cisco Nexus switch would be similar, so if you are a Cisco guy I'd be happy to hear from you.
I have installed Rancid (http://www.shrubbery.net/rancid/) on a machine here and I am grabbing switch configs every hour. This means that:
- There is an ssh login.
- Then the switch goes to enable mode.
- Then a show run is performed.
All of that uses CPU. My boss has asked me: Am I impacting latency? How do I know?
I don't think I am impacting latency, but I don't know that for sure. I have taken it on faith that I am not; that's why the ASICs are there, to do the heavy lifting and bring some determinism to switching speeds. Of course, some technologies could not be ASIC'ed like NAT but let's assume we are not doing that.
Our machines connected to the switches use a few different VLANs, and they need rather straightforward IP services I'd say: exchanging TCP and multicast UDP data- that's all. (Besides the usual supporting cast such as ARP that are necessary for TCP and UDP to work).