In this, javentre writes about the reporting of the traffic on Ethernet interfaces, and that because the counter doesn't include ethernet overhead, the 30 sec rate reported by the show int command isn't an accurate measure to determine if the link is saturated.

http://networking.ventrefamily.com/2010 ... alyst.html

My question, can SNMP get the actual utilization? Or is it a similar situation where overhead isn't reported? I understand there's a MIB that controls what is requested by SNMP but I haven't found this aspect discussed in my cursory search.

It should be pretty to figure out.

Get a quiet interface on a device. Find a target device in your subnet, one where you have an ARP entry for it and the target has a firewall blocking icmp (we don't want a reply), then send 1 ping of a known size. If you use a lab router where you have no target hosts, just nail up an arp entry for the end node, and send away. Just make sure you've disabled things like CDP/LLDP/DTP/etc.

If you poll the ifoutoctets before and after, we should get the answer.

I'm pretty swamped right now, but I'll do a blog entry with my findings for various platforms.

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Cool thanks, I'll try it this weekend.

Report back with your observations

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