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Cisco Port-Channel utilization, universally incorrect in Orion?

I just was thinking about this as I was checking out the utilization on a few port-channels. I noticed that Solarwinds will take (for instance) a port-channel with 2 1gb interfaces and call it 2GB and show utilization that way. For example I was looking at one of mine that was exactly that and it was at 50% utilization (this is what got me thinking).

For Cisco port-channels anyway (different vendors do different things as do the different OS's) a 2GB port channel is not a 2GB path. It is 2 1GB paths that load balance so that communications are balanced across them but this is not per packet load balancing and is usually based on mac or L3 info if you configure it for more balance but even then 1 communication goes over one port so that the same communication if it happens everyday will always go over the same channel usually (unless you have a switch that will get down to the source and destination port for the hash).

So my long winded point here being, showing a 2GB port channel at 50% utilization is incorrect. Attached is a doc I made of one of my switches showing this. You will see the port channel shows about 50% utilization which would make you think things are fine but the other 2 pics will show you how 1 link is twiddling its thumbs while the other is near capacity. So showing an interface like this can fool you into thinking things are fine when they may not be.[View:/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.01.75.26/portchannel-.doc]

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fcaron

Well, if you keep asking for more traffic and it keeps saturating your port #1 (the one at 80%), because load balancing does not have fine-grain -enough granularity, I suppose at some point in time, the load balancer will start using port #2 (otherwise Cisco's port-channel mechanism is purely and simply broken).

If this is true, averaging the 2 makes sense, because you will stil have capacity until both are close to 100%, and th average of teh port channel wil be close to 100%.

How else would you expect NPM to report Utilization at the port channel level? The max vs. the average?

Donald_Francis

No actually it does not work like that. A numerical value is created from the options used to balance against (depends on platform capability and configuration) and with that value it will fire everything down one pipe for that communication. And as you may be thinking if the load balancing info is being used over and over (IE going to or from the same host each time) it will always go down the same pipe.

But the fact remains a 2gb port-channel (in Cisco terms) is 2 1gb channels unless you are doing per packet load balancing.

So I think it makes the chart technically incorrect in the case of Cisco and most port-channels people use as it might not represent true utilization however that does not mean the overall utilization number is worthless just sort of misrepresenting and might not clue you into an issue you are actually having.

How do you solve that? My suggestion would be to have a special chart for port-channels even if they have to be manually configured where you could basically create a port channel in Orion and add members to it so that when displayed it might be something like combining all the pics I had in the word doc. That being overall utilization (I would not get rid of that figure it is still useful) and then display a chart for each member link.

Just my 2 cents. I do not think there is anything broken, just misleading if you go solely by the port-channel utilization and that would be bad because you may have an issue and not realize it.

Donald_Francis

Maybe the answer is to possibly have an option that defaults to the Cisco default but gives you the ability to change the way Orion displays the detailed view of the interface/utilization per interface.

That way if you are running per packet or per destination you will see the correct thing.

The reason I am so adamant about this is that the most basic tool that is most widely used is the monitoring of bandwidth utilization. If that is wrong I can see where it would just cause confusion, IE hey my port-channel is slow but I do not know why because it is only 50% utilized.