Slowness of ICA sessions when connecting to Citrix XenApp 7.15 due to Interface Flaps on NetScaler

Hi Guys ,


Today I am writing about an very critical issue due to which we were not able to migrate to Xenapp 7.15 from Xenapp 6.5 . We have multiple sites where ours offices are located and on one of these sites we were constantly seeing slowness and screen flickering . Every time we will try to migrate we will get complaints that the new environment is very slow. Even though we had hybrid environment with half of the environment on AWS and half on VMware .

To get to the root of the this issue I started troubleshooting from basics :

So the issue is as follows:



Users from a specific site: Manila facing slowness issue, working with published apps .



Half of the Citrix components are hosted on Amazon cloud.



1) I checked the direct connection to Storefront server and confirmed that the apps were working as expected.

2) Verified that one of the users from the site in question, was able to launch and work on the published app, without any issue.

3) Confirmed that the users accessing the same resource from other sites (Australia and Singapore) are not facing such issue.

4.) But then again the slowness issue started after all users in the site had logged in indicating that the issue was happeningĀ  intermittently .

5.) I then decided to check Netscaler for any clues and I found the following issues by observing netscaler logs :

–VPX 1000(Running on VMware) Ns 12.0 53.13 –Service/Service Group had flapped.

–No Core/Crash files found.

–Did check for newnslog and found that the interface 0/1 and 1/1 did flap during the causing the service/Service group to flap.

–Meanwhile when I was checking the netscaler the interface flapped again causing the Service to flap.

–Checked and found that this is known issue when the Adaptor type on VMware is E1000 where was Netscaler was hosted.It was a standalone virtual device with HA configuration .

–To fix the issue change the adapter type from E1000 to VMXNET3 VMware ESXi.

Reference Article –

–After following the article you will able to able to get rid of the Service Flap issue on netscaler . Basically that was causing the slowness and flickering on our sites . But something else happened when we shutdown our Netscaler device and added the new adapter as you cannot change the adapter, you need to remove and add . Which basically meant that after adding the adapters the MAC address changed which resulted in loss of License and whole site went down.

So summary

–NetScaler license was lost post rebooting the NetScaler once the adaptor was changed from E1000 to VMXNET3 and later the configuration was restored.

–The reason license was lost because the license is generated for the MAC address of the VPX interface.

–So once the adaptor was changed the MAC address of the interface was changed which caused the VPX to loose the license.

–We did check the config and everything did look good. But the intermediate and Root cert was not there.

–Installed the intermediate and Root Certs on NetScaler and linked it with the Server Cert.

–Please take a note of MAC address when you are adding the new adapter so that you can put back the same MAC address to which the license was attached.


So basically you need to keep that License is attached to MAC address and when you change the adapter the MAC address will change and you need to have a proper backup in place to restore the configuration of the netscaler .


Or else please note down the MAC address and then you can replace the same MAC which was there initially .


I hope this help you while making this big change .


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Website Powered by

Up ↑

%d bloggers like this: