Hello!
I know what you are thinking, in what situation would a NetScaler appliance start to drop traffic? I thought this was a simple one, but one of my customers logged a support ticket for this issue. Maybe, someone else has similar issues and a short piece online would explain this in 2minutes and save them from raising a support case? Save the support case for something they can get their teeth into.
What is the scenario?
You have a NetScaler, you have a bunch of clients/customers and you have 'something that they need to get access to'. The word 'something' could be anything! Let's say that the NetScaler is doing a job, in this case, load-balancing traffic. Maybe it looks like this:
This seems pretty simple, but what is going on? The clients on the left-hand side are accessing some kind of application served by the three servers on the right-hand side.
The NetScaler has been helpfully labelled as 'load balancing' its job in this case. What does the NetScaler actually do? It's in the middle of this conversation between the clients and the server and can make some decisions about how traffic is directed to which application server. It monitors the servers, to ensure that they are available and that the application is online. This can then ensure that the client is sent to the best server for its connection.
Obviously, in this case I am showing three clients and three servers, we are 1:1! In the real world, there might be a lot more clients...
This layout with the NetScaler in the middle of the conversation is an ideal spot for it to do many other useful things, but let's keep this simple for this short article.
Naturally, traffic flows through the NetScaler in order for it to do its job. When the NetScaler was created, a decision was made to say that it would be sized based on the amount of throughput that it could handle. These throughput numbers range from a few megabytes up to hundreds of Gigabytes. Let's put some numbers on the example above. If it has a 25 megabytes rating what happens when it reaches 26 megabytes? The traffic needs to go somewhere.
Typically, the traffic is dropped. It has reached its limit. Yikes!
What can you do?
There are a couple of options.
Reduce the load on the appliance
Get a bigger BOAT! (sorry, Jaws quote...appliance).
Option one is simply dropping the amount of users loading up the appliance. This isn't always a viable option, option two just gives the NetScaler more capability to do its job. This would raise the software limit that the NetScaler has, in a lot of cases this is a simple license configuration change.
How does the NetScaler Tell you?
The appliance logs everything, checking the ns.log would be one option. Check the appliance console is another. It can get quite 'noisy' in the console to say, 'I'm dropping traffic'!
You could also have ADM (our free management platform) on the case, it has a dashboard to tell you exactly this.
Summary
Dropped traffic is typically due to traffic reaching its limit for your appliance. There are different appliance types, something like a virtual appliance (VPX in NetScaler lingo) can scale from a few megabytes to one hundred gigabytes depending on the platform.
NetScaler is a commercial product, so there will be a cost for having more capability. ADM has some great dashboards to give you visibility of these events.
Have a good one!