Chapter 23. LANZ

If you’ve read the chapter on buffers (Chapter 3), you know that they can be a benefit or bane, depending on a lot of factors. When buffers in a switch become a problem, it can be very difficult to isolate the problem because there usually aren’t detailed counters that show the buffer contents. When running quality of service (QoS) on routers, there are all kinds of commands to run that will show you the status of your buffers, but those buffers are software constructs that take memory from the system. The buffers I’m referring to here are hardware switch interface buffers. Let’s dig in, and I’ll show you what I mean.

Here’s the output from the show interface command on an Arista 7280R. As you can see, there is no mention of buffers:

Arista-1#sho int e48 Ethernet48 is up, line protocol is up (connected) Hardware is Ethernet, address is 2899.3abe.a026 Description: desc [ Arista-2 ] Internet address is Broadcast address is IP MTU 1500 bytes , BW 10000000 kbit Full-duplex, 10Gb/s, auto negotiation: off, uni-link: disabled Up 19 hours, 56 minutes, 8 seconds Loopback Mode : None 11 link status changes since last clear Last clearing of "show interface" counters 13 days, 20:40:55 ago 5 minutes input rate 55 bps (0.0% with framing overhead), 0 packets/sec 5 minutes output rate 60 bps (0.0% with framing overhead), 0 packets/sec 74213421 packets input, 110899750528 bytes Received 2 broadcasts, 8437 multicast 0 runts, 0 giants 0 input errors, ...

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