[a-nsp] VLAN in SNMP Interface Table

[Doug McIntyre]

I'd count the packets exiting a port as doing some work.

Maybe a better analogy would be you have a bunch of envelopes sent
through the post office. You are asking a counter to see how many
pieces of paper are in each envelope. The post office only delivers
the envelopes, so we have a total count of envelopes. Only if we need
to burst open the envelopes (layer-3) and start routing the pieces of paper
based on their top tag, will we have counters on them. As long as the
post office keeps forwarding intact envelopes (ie. layer-2), we won't have
visibility into inside.




On Mon, Dec 09, 2019 at 07:40:00AM -0600, Mike Hammett wrote:
> If the first paragraph were true, we'd never have port counters on a switch. 
> 
> 
> 
> 
> ----- 
> Mike Hammett 
> Intelligent Computing Solutions 
> 
> Midwest Internet Exchange 
> 
> The Brothers WISP 
> 
> ----- Original Message -----
> 
> From: "Doug McIntyre" <merlyn at geeks.org> 
> To: arista-nsp at puck.nether.net 
> Sent: Monday, December 9, 2019 7:36:05 AM 
> Subject: Re: [a-nsp] VLAN in SNMP Interface Table 
> 
> On Sun, Dec 08, 2019 at 06:02:47PM -0600, Mike Hammett wrote: 
> > This looks like it's only on layer 3 interfaces, which doesn't do me a whole lot of good. 
> 
> 
> I don't know of any hardware that keeps track of layer-2 VLAN packet 
> counts going through the switch. Generally, stats are updated on times 
> when switches have to _do_ something. Forwarding along layer-2 is 
> usually done in ASICs and the switch doesn't do anything special for 
> decoding the VLAN headers. OOTH, doing a layer-3 routing termination 
> is doing something, which is where I measure everything, on the 
> layer-3 edge. And every type of hardware I touch can monitor that. 
> 
> As posted before, if you need this sort of thing, you'll probably have 
> to go to sflow type collectors in order to get what you want. Or 
> consider making your network do layer-3 VLAN terminations somewhere so 
> that you can measure it. 
> 
> Perhaps there is some weird EVPN/vxlan setup you could make that the 
> switch will have to do punting of traffic out to a VTEP, and you could 
> measure those counts, but I have zero experience monitoring such a setup. 
> 
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